diff --git a/.clang-format-ignore b/.clang-format-ignore
index ee5d4763575f..e78ab84b7704 100644
--- a/.clang-format-ignore
+++ b/.clang-format-ignore
@@ -35,6 +35,10 @@ browser/extensions/mortar/ppapi/.*
 db/sqlite3/src/.*
 devtools/client/sourceeditor/codemirror/.*
 devtools/client/sourceeditor/tern/.*
+dom/media/gmp/widevine-adapter/content_decryption_module.h
+dom/media/gmp/widevine-adapter/content_decryption_module_export.h
+dom/media/gmp/widevine-adapter/content_decryption_module_ext.h
+dom/media/gmp/widevine-adapter/content_decryption_module_proxy.h
 editor/libeditor/tests/browserscope/lib/richtext/.*
 editor/libeditor/tests/browserscope/lib/richtext2/.*
 extensions/spellcheck/hunspell/src/.*
diff --git a/.eslintignore b/.eslintignore
index 694ad29da90c..26d524fc3134 100644
--- a/.eslintignore
+++ b/.eslintignore
@@ -120,8 +120,6 @@ devtools/shared/qrcode/tests/mochitest/test_decode.html
 devtools/shared/tests/mochitest/*.html
 devtools/shared/webconsole/test/test_*.html
 
-# Soon to be removed
-devtools/client/commandline/**
 # Soon to be removed, the new/ directory is explicitly excluded below due to
 # also being an imported repository.
 devtools/client/debugger/**
@@ -136,6 +134,9 @@ devtools/client/webide/preferences/**
 devtools/shared/preferences/**
 devtools/startup/preferences/devtools-startup.js
 
+# Ignore devtools generated code
+devtools/shared/css/generated/properties-db.js
+
 # Ignore devtools third-party libs
 devtools/shared/jsbeautify/*
 devtools/shared/acorn/*
diff --git a/accessible/ipc/DocAccessibleParent.cpp b/accessible/ipc/DocAccessibleParent.cpp
index 44bd73fa6b6f..259d62c575dd 100644
--- a/accessible/ipc/DocAccessibleParent.cpp
+++ b/accessible/ipc/DocAccessibleParent.cpp
@@ -760,7 +760,7 @@ DocAccessibleParent::SendParentCOMProxy()
   }
 
 #if defined(MOZ_CONTENT_SANDBOX)
-  mParentProxyStream = std::move(holder.GetPreservedStream());
+  mParentProxyStream = holder.GetPreservedStream();
 #endif // defined(MOZ_CONTENT_SANDBOX)
 }
 
diff --git a/accessible/ipc/win/HandlerProvider.cpp b/accessible/ipc/win/HandlerProvider.cpp
index cf5e27bea746..17ff81dac0af 100644
--- a/accessible/ipc/win/HandlerProvider.cpp
+++ b/accessible/ipc/win/HandlerProvider.cpp
@@ -247,7 +247,7 @@ HandlerProvider::BuildDynamicIA2Data(DynamicIA2Data* aOutIA2Data)
     return FAILED(hr);
   };
 
-  auto cleanup = [this, aOutIA2Data]() -> void {
+  auto cleanup = [aOutIA2Data]() -> void {
     CleanupDynamicIA2Data(*aOutIA2Data);
   };
 
diff --git a/accessible/ipc/win/PlatformChild.cpp b/accessible/ipc/win/PlatformChild.cpp
index 1dfc8baf827b..f2c79c69a67e 100644
--- a/accessible/ipc/win/PlatformChild.cpp
+++ b/accessible/ipc/win/PlatformChild.cpp
@@ -70,14 +70,14 @@ PlatformChild::PlatformChild()
 
   UniquePtr<mozilla::mscom::RegisteredProxy> customProxy;
   mozilla::mscom::EnsureMTA([&customProxy]() -> void {
-    customProxy = std::move(mozilla::mscom::RegisterProxy());
+    customProxy = mozilla::mscom::RegisterProxy();
   });
   mCustomProxy = std::move(customProxy);
 
   // IA2 needs to be registered in both the main thread's STA as well as the MTA
   UniquePtr<mozilla::mscom::RegisteredProxy> ia2ProxyMTA;
   mozilla::mscom::EnsureMTA([&ia2ProxyMTA]() -> void {
-    ia2ProxyMTA = std::move(mozilla::mscom::RegisterProxy(L"ia2marshal.dll"));
+    ia2ProxyMTA = mozilla::mscom::RegisterProxy(L"ia2marshal.dll");
   });
   mIA2ProxyMTA = std::move(ia2ProxyMTA);
 }
diff --git a/accessible/ipc/win/ProxyAccessible.cpp b/accessible/ipc/win/ProxyAccessible.cpp
index 9724bb6b4f52..45b7bf7857c1 100644
--- a/accessible/ipc/win/ProxyAccessible.cpp
+++ b/accessible/ipc/win/ProxyAccessible.cpp
@@ -244,7 +244,7 @@ ProxyAccessible::BoundsInCSSPixels()
   }
 
   nsIntRect rect;
-  HRESULT hr = custom->get_boundsInCSSPixels(&rect.x, &rect.y, &rect.width, &rect.height);
+  Unused << custom->get_boundsInCSSPixels(&rect.x, &rect.y, &rect.width, &rect.height);
   return rect;
 }
 
@@ -416,7 +416,7 @@ ProxyAccessible::RelationByType(RelationType aType) const
   }
   CoTaskMemFree(targets);
 
-  return std::move(proxies);
+  return proxies;
 }
 
 double
diff --git a/accessible/windows/msaa/AccessibleWrap.cpp b/accessible/windows/msaa/AccessibleWrap.cpp
index 29a778b25f66..ccd4a4f378c3 100644
--- a/accessible/windows/msaa/AccessibleWrap.cpp
+++ b/accessible/windows/msaa/AccessibleWrap.cpp
@@ -1770,7 +1770,7 @@ AccessibleWrap::InvalidateHandlers()
     if (hr == CO_E_OBJNOTCONNECTED || hr == kErrorServerDied) {
       sHandlerControllers->RemoveElement(controller);
     } else {
-      NS_WARN_IF(FAILED(hr));
+      Unused << NS_WARN_IF(FAILED(hr));
     }
   }
 }
diff --git a/browser/app/profile/firefox.js b/browser/app/profile/firefox.js
index 6d9d1fd3dd01..a29045ae1bfd 100644
--- a/browser/app/profile/firefox.js
+++ b/browser/app/profile/firefox.js
@@ -1737,10 +1737,6 @@ pref("app.shield.optoutstudies.enabled", true);
 pref("app.shield.optoutstudies.enabled", false);
 #endif
 
-// Savant Shield study preferences
-pref("shield.savant.enabled", false);
-pref("shield.savant.loglevel", "warn");
-
 // Multi-lingual preferences
 pref("intl.multilingual.enabled", false);
 
diff --git a/browser/base/content/browser.js b/browser/base/content/browser.js
index 3d11006b10bc..5db666184d07 100644
--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -19,6 +19,7 @@ XPCOMUtils.defineLazyModuleGetters(this, {
   BrowserUsageTelemetry: "resource:///modules/BrowserUsageTelemetry.jsm",
   BrowserUtils: "resource://gre/modules/BrowserUtils.jsm",
   BrowserWindowTracker: "resource:///modules/BrowserWindowTracker.jsm",
+  CFRPageActions: "resource://activity-stream/lib/CFRPageActions.jsm",
   CharsetMenu: "resource://gre/modules/CharsetMenu.jsm",
   Color: "resource://gre/modules/Color.jsm",
   ContentSearch: "resource:///modules/ContentSearch.jsm",
@@ -4817,6 +4818,8 @@ var XULBrowserWindow = {
                  CustomizationHandler.isCustomizing()) {
         gCustomizeMode.exit();
       }
+
+      CFRPageActions.updatePageActions(gBrowser.selectedBrowser);
     }
     UpdateBackForwardCommands(gBrowser.webNavigation);
     ReaderParent.updateReaderButton(gBrowser.selectedBrowser);
diff --git a/browser/base/content/browser.xul b/browser/base/content/browser.xul
index 61b518a7947b..c3b60cbd56a0 100644
--- a/browser/base/content/browser.xul
+++ b/browser/base/content/browser.xul
@@ -634,6 +634,16 @@ xmlns="http://www.w3.org/1999/xhtml"
                 accesskey="&syncSyncNowItem.accesskey;"
                 id="syncedTabsRefreshFilter"/>
     </menupopup>
+
+    <hbox id="statuspanel" inactive="true" layer="true">
+      <hbox id="statuspanel-inner">
+        <label id="statuspanel-label"
+               role="status"
+               aria-live="off"
+               flex="1"
+               crop="end"/>
+      </hbox>
+    </hbox>
   </popupset>
   <box id="appMenu-viewCache" hidden="true"/>
 
@@ -1261,37 +1271,7 @@ xmlns="http://www.w3.org/1999/xhtml"
         <tabbox id="tabbrowser-tabbox"
                 flex="1" eventnode="document" tabcontainer="tabbrowser-tabs">
           <tabpanels id="tabbrowser-tabpanels"
-                     flex="1" class="plain" selectedIndex="0">
-            <notificationbox flex="1" notificationside="top">
-              <!-- Set large flex to allow the devtools toolbox to set a flex attribute.
-                   We don't want the toolbox to actually take up free space, but we do want it to collapse when the window shrinks, and with flex=0 it can't.
-                   When the toolbox is on the bottom it's a sibling of browserSidebarContainer,
-                   and when it's on the side it's a sibling of browserContainer.  -->
-              <hbox flex="10000" class="browserSidebarContainer">
-                <vbox flex="10000" class="browserContainer">
-                  <stack flex="1" class="browserStack">
-                    <browser id="tabbrowser-initialBrowser" type="content"
-                             message="true" messagemanagergroup="browsers"
-                             primary="true" blank="true"
-                             tooltip="aHTMLTooltip"
-                             contextmenu="contentAreaContextMenu"
-                             autocompletepopup="PopupAutoComplete"
-                             selectmenulist="ContentSelectDropdown"
-                             datetimepicker="DateTimePickerPanel"/>
-                  </stack>
-                  <hbox id="statuspanel" inactive="true" layer="true">
-                    <hbox id="statuspanel-inner">
-                      <label id="statuspanel-label"
-                             role="status"
-                             aria-live="off"
-                             flex="1"
-                             crop="end"/>
-                    </hbox>
-                  </hbox>
-                </vbox>
-              </hbox>
-            </notificationbox>
-          </tabpanels>
+                     flex="1" class="plain" selectedIndex="0"/>
         </tabbox>
       </vbox>
       <vbox id="browser-border-end" hidden="true" layer="true"/>
diff --git a/browser/base/content/tabbrowser.js b/browser/base/content/tabbrowser.js
index 8ac2eadac0eb..c4b962f5a180 100644
--- a/browser/base/content/tabbrowser.js
+++ b/browser/base/content/tabbrowser.js
@@ -282,50 +282,40 @@ window._gBrowser = {
     return this._selectedBrowser;
   },
 
-  get initialBrowser() {
-    delete this.initialBrowser;
-    return this.initialBrowser = document.getElementById("tabbrowser-initialBrowser");
-  },
-
   _setupInitialBrowserAndTab() {
-    let browser = this.initialBrowser;
-    this._selectedBrowser = browser;
-
-    browser.permanentKey = {};
+    // Bug 1362774 will adjust this to only set `uriIsAboutBlank` when
+    // necessary. For now, we always pass it.
+    let browser = this._createBrowser({uriIsAboutBlank: true});
+    browser.setAttribute("primary", "true");
+    browser.setAttribute("blank", "true");
     browser.droppedLinkHandler = handleDroppedLink;
     browser.loadURI = _loadURI.bind(null, browser);
 
-    let autoScrollPopup = browser._createAutoScrollPopup();
-    autoScrollPopup.id = "autoscroller";
-    document.getElementById("mainPopupSet").appendChild(autoScrollPopup);
-    browser.setAttribute("autoscrollpopup", autoScrollPopup.id);
-
-    this._defaultBrowserAttributes = {
-      autoscrollpopup: "",
-      contextmenu: "",
-      datetimepicker: "",
-      message: "",
-      messagemanagergroup: "",
-      selectmenulist: "",
-      tooltip: "",
-      type: "",
-    };
-    for (let attribute in this._defaultBrowserAttributes) {
-      this._defaultBrowserAttributes[attribute] = browser.getAttribute(attribute);
-    }
+    let uniqueId = this._generateUniquePanelID();
+    let notificationbox = this.getNotificationBox(browser);
+    notificationbox.id = uniqueId;
+    this.tabpanels.appendChild(notificationbox);
 
     let tab = this.tabs[0];
-    this._selectedTab = tab;
-
-    let uniqueId = this._generateUniquePanelID();
-    this.tabpanels.children[0].id = uniqueId;
     tab.linkedPanel = uniqueId;
+    this._selectedTab = tab;
+    this._selectedBrowser = browser;
     tab.permanentKey = browser.permanentKey;
     tab._tPos = 0;
     tab._fullyOpen = true;
     tab.linkedBrowser = browser;
     this._tabForBrowser.set(browser, tab);
 
+    this._appendStatusPanel();
+
+    this.initialBrowser = browser;
+
+    let autoScrollPopup = browser._createAutoScrollPopup();
+    autoScrollPopup.id = "autoscroller";
+    document.getElementById("mainPopupSet").appendChild(autoScrollPopup);
+    browser.setAttribute("autoscrollpopup", autoScrollPopup.id);
+    this._autoScrollPopup = autoScrollPopup;
+
     // Hook the browser up with a progress listener.
     let tabListener = new TabProgressListener(tab, browser, true, false);
     let filter = Cc["@mozilla.org/appshell/component/browser-status-filter;1"]
@@ -1014,7 +1004,6 @@ window._gBrowser = {
         }
       });
       newTab.dispatchEvent(event);
-      Services.telemetry.recordEvent("savant", "tab", "select", null, { subcategory: "frame" });
 
       this._tabAttrModified(oldTab, ["selected"]);
       this._tabAttrModified(newTab, ["selected"]);
@@ -1812,8 +1801,17 @@ window._gBrowser = {
     let b = document.createXULElement("browser");
     b.permanentKey = {};
 
-    for (let attribute in this._defaultBrowserAttributes) {
-      b.setAttribute(attribute, this._defaultBrowserAttributes[attribute]);
+    const defaultBrowserAttributes = {
+      contextmenu: "contentAreaContextMenu",
+      datetimepicker: "DateTimePickerPanel",
+      message: "true",
+      messagemanagergroup: "browsers",
+      selectmenulist: "ContentSelectDropdown",
+      tooltip: "aHTMLTooltip",
+      type: "content",
+    };
+    for (let attribute in defaultBrowserAttributes) {
+      b.setAttribute(attribute, defaultBrowserAttributes[attribute]);
     }
 
     if (userContextId) {
@@ -1843,6 +1841,10 @@ window._gBrowser = {
     if (!isPreloadBrowser) {
       b.setAttribute("autocompletepopup", "PopupAutoComplete");
     }
+    if (this._autoScrollPopup) {
+      b.setAttribute("autoscrollpopup", this._autoScrollPopup.id);
+    }
+
 
     /*
      * This attribute is meant to describe if the browser is the
@@ -1889,13 +1891,17 @@ window._gBrowser = {
     stack.appendChild(b);
     stack.setAttribute("flex", "1");
 
-    // Create the browserContainer
+    // We set large flex on both containers to allow the devtools toolbox to
+    // set a flex attribute. We don't want the toolbox to actually take up free
+    // space, but we do want it to collapse when the window shrinks, and with
+    // flex=0 it can't. When the toolbox is on the bottom it's a sibling of
+    // browserSidebarContainer, and when it's on the side it's a sibling of
+    // browserContainer.
     let browserContainer = document.createXULElement("vbox");
     browserContainer.className = "browserContainer";
     browserContainer.appendChild(stack);
     browserContainer.setAttribute("flex", "10000");
 
-    // Create the sidebar container
     let browserSidebarContainer = document.createXULElement("hbox");
     browserSidebarContainer.className = "browserSidebarContainer";
     browserSidebarContainer.appendChild(browserContainer);
@@ -2472,7 +2478,6 @@ window._gBrowser = {
     // even if the event listener opens or closes tabs.
     let evt = new CustomEvent("TabOpen", { bubbles: true, detail: eventDetail || {} });
     t.dispatchEvent(evt);
-    Services.telemetry.recordEvent("savant", "tab", "open", null, { subcategory: "frame" });
 
     if (!usingPreloadedContent && originPrincipal && aURI) {
       let { URI_INHERITS_SECURITY_CONTEXT } = Ci.nsIProtocolHandler;
@@ -2886,7 +2891,6 @@ window._gBrowser = {
     // inspect the tab that's about to close.
     var evt = new CustomEvent("TabClose", { bubbles: true, detail: { adoptedBy: aAdoptedByTab } });
     aTab.dispatchEvent(evt);
-    Services.telemetry.recordEvent("savant", "tab", "close", null, { subcategory: "frame" });
 
     if (this.tabs.length == 2) {
       // We're closing one of our two open tabs, inform the other tab that its
diff --git a/browser/components/newtab/data/content/assets/glyph-webextension-16.svg b/browser/components/newtab/data/content/assets/glyph-webextension-16.svg
index c057f148e7e7..1b65dd449041 100644
--- a/browser/components/newtab/data/content/assets/glyph-webextension-16.svg
+++ b/browser/components/newtab/data/content/assets/glyph-webextension-16.svg
@@ -1 +1 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16"><path fill="context-fill" d="M14.5 8c-.971 0-1 1-1.75 1a.765.765 0 0 1-.75-.75V5a1 1 0 0 0-1-1H7.75A.765.765 0 0 1 7 3.25c0-.75 1-.779 1-1.75C8 .635 7.1 0 6 0S4 .635 4 1.5c0 .971 1 1 1 1.75a.765.765 0 0 1-.75.75H1a1 1 0 0 0-1 1v2.25A.765.765 0 0 0 .75 8c.75 0 .779-1 1.75-1C3.365 7 4 7.9 4 9s-.635 2-1.5 2c-.971 0-1-1-1.75-1a.765.765 0 0 0-.75.75V15a1 1 0 0 0 1 1h3.25a.765.765 0 0 0 .75-.75c0-.75-1-.779-1-1.75 0-.865.9-1.5 2-1.5s2 .635 2 1.5c0 .971-1 1-1 1.75a.765.765 0 0 0 .75.75H11a1 1 0 0 0 1-1v-3.25a.765.765 0 0 1 .75-.75c.75 0 .779 1 1.75 1 .865 0 1.5-.9 1.5-2s-.635-2-1.5-2z"/></svg>
\ No newline at end of file
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 16 16"><path fill="context-fill" fill-opacity="context-fill-opacity" d="M14.5 8c-.971 0-1 1-1.75 1a.765.765 0 0 1-.75-.75V5a1 1 0 0 0-1-1H7.75A.765.765 0 0 1 7 3.25c0-.75 1-.779 1-1.75C8 .635 7.1 0 6 0S4 .635 4 1.5c0 .971 1 1 1 1.75a.765.765 0 0 1-.75.75H1a1 1 0 0 0-1 1v2.25A.765.765 0 0 0 .75 8c.75 0 .779-1 1.75-1C3.365 7 4 7.9 4 9s-.635 2-1.5 2c-.971 0-1-1-1.75-1a.765.765 0 0 0-.75.75V15a1 1 0 0 0 1 1h3.25a.765.765 0 0 0 .75-.75c0-.75-1-.779-1-1.75 0-.865.9-1.5 2-1.5s2 .635 2 1.5c0 .971-1 1-1 1.75a.765.765 0 0 0 .75.75H11a1 1 0 0 0 1-1v-3.25a.765.765 0 0 1 .75-.75c.75 0 .779 1 1.75 1 .865 0 1.5-.9 1.5-2s-.635-2-1.5-2z"/></svg>
\ No newline at end of file
diff --git a/browser/components/newtab/lib/CFRPageActions.jsm b/browser/components/newtab/lib/CFRPageActions.jsm
new file mode 100644
index 000000000000..5be4c035b82e
--- /dev/null
+++ b/browser/components/newtab/lib/CFRPageActions.jsm
@@ -0,0 +1,247 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+const POPUP_NOTIFICATION_ID = "contextual-feature-recommendation";
+
+const DELAY_BEFORE_EXPAND_MS = 1000;
+const DURATION_OF_EXPAND_MS = 5000;
+
+/**
+ * A WeakMap from browsers to {host, recommendation} pairs. Recommendations are
+ * defined in the ExtensionDoorhanger.schema.json.
+ *
+ * A recommendation is specific to a browser and host and is active until the
+ * given browser is closed or the user navigates (within that browser) away from
+ * the host.
+ */
+const RecommendationMap = new WeakMap();
+
+/**
+ * A WeakMap from windows to their CFR PageAction.
+ */
+const PageActionMap = new WeakMap();
+
+/**
+ * We need one PageAction for each window
+ */
+class PageAction {
+  constructor(win, dispatchToASRouter) {
+    this.window = win;
+    this.urlbar = win.document.getElementById("urlbar");
+    this.container = win.document.getElementById("contextual-feature-recommendation");
+    this.button = win.document.getElementById("cfr-button");
+    this.label = win.document.getElementById("cfr-label");
+
+    this._dispatchToASRouter = dispatchToASRouter;
+    this._popupStateChange = this._popupStateChange.bind(this);
+    this._collapse = this._collapse.bind(this);
+    this._handleClick = this._handleClick.bind(this);
+
+    // Saved timeout IDs for scheduled state changes, so they can be cancelled
+    this.stateTransitionTimeoutIDs = [];
+
+    this.container.onclick = this._handleClick;
+  }
+
+  async show(notificationText, shouldExpand = false) {
+    this.container.hidden = false;
+
+    this.label.value = notificationText;
+
+    // Wait for layout to flush to avoid a synchronous reflow then calculate the
+    // label width. We can safely get the width even though the recommendation is
+    // collapsed; the label itself remains full width (with its overflow hidden)
+    await this.window.promiseDocumentFlushed;
+    const [{width}] = this.label.getClientRects();
+    this.urlbar.style.setProperty("--cfr-label-width", `${width}px`);
+
+    if (shouldExpand) {
+      this._clearScheduledStateChanges();
+
+      // After one second, expand
+      this._expand(DELAY_BEFORE_EXPAND_MS);
+
+      // Five seconds later, collapse again
+      this._collapse(DELAY_BEFORE_EXPAND_MS + DURATION_OF_EXPAND_MS);
+    }
+  }
+
+  hide() {
+    this.container.hidden = true;
+    this._clearScheduledStateChanges();
+    this.urlbar.removeAttribute("cfr-recommendation-state");
+  }
+
+  _expand(delay = 0) {
+    if (!delay) {
+      // Non-delayed state change overrides any scheduled state changes
+      this._clearScheduledStateChanges();
+      this.urlbar.setAttribute("cfr-recommendation-state", "expanded");
+    } else {
+      this.stateTransitionTimeoutIDs.push(this.window.setTimeout(() => {
+        this.urlbar.setAttribute("cfr-recommendation-state", "expanded");
+      }, delay));
+    }
+  }
+
+  _collapse(delay = 0) {
+    if (!delay) {
+      // Non-delayed state change overrides any scheduled state changes
+      this._clearScheduledStateChanges();
+      if (this.urlbar.getAttribute("cfr-recommendation-state") === "expanded") {
+        this.urlbar.setAttribute("cfr-recommendation-state", "collapsed");
+      }
+    } else {
+      this.stateTransitionTimeoutIDs.push(this.window.setTimeout(() => {
+        if (this.urlbar.getAttribute("cfr-recommendation-state") === "expanded") {
+          this.urlbar.setAttribute("cfr-recommendation-state", "collapsed");
+        }
+      }, delay));
+    }
+  }
+
+  _clearScheduledStateChanges() {
+    while (this.stateTransitionTimeoutIDs.length > 0) {
+      // clearTimeout is safe even with invalid/expired IDs
+      this.window.clearTimeout(this.stateTransitionTimeoutIDs.pop());
+    }
+  }
+
+  // This is called when the popup closes as a result of interaction _outside_
+  // the popup, e.g. by hitting <esc>
+  _popupStateChange(state) {
+    if (["dismissed", "removed"].includes(state)) {
+      this._collapse();
+    }
+  }
+
+  /**
+   * Respond to a user click on the recommendation by showing a doorhanger/
+   * popup notification
+   */
+  _handleClick(event) {
+    const browser = this.window.gBrowser.selectedBrowser;
+    if (!RecommendationMap.has(browser)) {
+      // There's no recommendation for this browser, so the user shouldn't have
+      // been able to click
+      this.hide();
+      return;
+    }
+    const {content} = RecommendationMap.get(browser);
+
+    // The recommendation should remain either collapsed or expanded while the
+    // doorhanger is showing
+    this._clearScheduledStateChanges();
+
+    // A hacky way of setting the popup anchor outside the usual url bar icon box
+    // See https://searchfox.org/mozilla-central/rev/847b64cc28b74b44c379f9bff4f415b97da1c6d7/toolkit/modules/PopupNotifications.jsm#42
+    browser.cfrpopupnotificationanchor = this.container;
+
+    const {primary, secondary} = content.buttons;
+
+    const mainAction = {
+      label: primary.label,
+      accessKey: primary.accessKey,
+      callback: () => this._dispatchToASRouter(primary.action)
+    };
+
+    const secondaryActions = [{
+      label: secondary.label,
+      accessKey: secondary.accessKey,
+      callback: this._collapse
+    }];
+
+    const options = {
+      popupIconURL: content.addon.icon,
+      hideClose: true,
+      eventCallback: this._popupStateChange
+    };
+
+    this.window.PopupNotifications.show(
+      browser,
+      POPUP_NOTIFICATION_ID,
+      content.text,
+      "cfr",
+      mainAction,
+      secondaryActions,
+      options
+    );
+  }
+}
+
+function isHostMatch(browser, host) {
+  return (browser.documentURI.scheme.startsWith("http") &&
+    browser.documentURI.host === host);
+}
+
+const CFRPageActions = {
+  // For testing purposes
+  RecommendationMap,
+  PageActionMap,
+
+  /**
+   * To be called from browser.js on a location change, passing in the browser
+   * that's been updated
+   */
+  updatePageActions(browser) {
+    const win = browser.ownerGlobal;
+    const pageAction = PageActionMap.get(win);
+    if (!pageAction || browser !== win.gBrowser.selectedBrowser) {
+      return;
+    }
+    if (RecommendationMap.has(browser)) {
+      const {host, content} = RecommendationMap.get(browser);
+      if (isHostMatch(browser, host)) {
+        // The browser has a recommendation specified with this host, so show
+        // the page action
+        pageAction.show(content.notification_text);
+      } else {
+        // The user has navigated away from the specified host in the given
+        // browser, so the recommendation is no longer valid and should be removed
+        RecommendationMap.delete(browser);
+        pageAction.hide();
+      }
+    } else {
+      // There's no recommendation specified for this browser, so hide the page action
+      pageAction.hide();
+    }
+  },
+
+  /**
+   * Add a recommendation specific to the given browser and host.
+   * @param browser             The browser for the recommendation
+   * @param host                The host for the recommendation
+   * @param recommendation      The recommendation to show
+   * @param dispatchToASRouter  A function to dispatch resulting actions to
+   * @param force               Force the recommendation to appear if the host doesn't match
+   * @return                    Did adding the recommendation succeed?
+   */
+  async addRecommendation(browser, host, recommendation, dispatchToASRouter, force = false) {
+    const win = browser.ownerGlobal;
+    if (browser !== win.gBrowser.selectedBrowser || !(force || isHostMatch(browser, host))) {
+      return false;
+    }
+    const {id, content} = recommendation;
+    RecommendationMap.set(browser, {id, host, content});
+    if (!PageActionMap.has(win)) {
+      PageActionMap.set(win, new PageAction(win, dispatchToASRouter));
+    }
+    await PageActionMap.get(win).show(recommendation.content.notification_text, true);
+    return true;
+  },
+
+  /**
+   * Clear all recommendations and hide all PageActions
+   */
+  clearRecommendations() {
+    for (const [win, pageAction] of PageActionMap) {
+      pageAction.hide();
+      PageActionMap.delete(win);
+    }
+    RecommendationMap.clear();
+  }
+};
+
+const EXPORTED_SYMBOLS = ["CFRPageActions"];
diff --git a/browser/components/nsBrowserGlue.js b/browser/components/nsBrowserGlue.js
index 1f2234879bd4..aebfeb6ba5e0 100644
--- a/browser/components/nsBrowserGlue.js
+++ b/browser/components/nsBrowserGlue.js
@@ -429,7 +429,6 @@ XPCOMUtils.defineLazyModuleGetters(this, {
   RemoteSettings: "resource://services-settings/remote-settings.js",
   SafeBrowsing: "resource://gre/modules/SafeBrowsing.jsm",
   Sanitizer: "resource:///modules/Sanitizer.jsm",
-  SavantShieldStudy: "resource:///modules/SavantShieldStudy.jsm",
   SessionStartup: "resource:///modules/sessionstore/SessionStartup.jsm",
   SessionStore: "resource:///modules/sessionstore/SessionStore.jsm",
   ShellService: "resource:///modules/ShellService.jsm",
@@ -525,9 +524,6 @@ const listeners = {
     "RemoteLogins:autoCompleteLogins": ["LoginManagerParent"],
     "RemoteLogins:removeLogin": ["LoginManagerParent"],
     "RemoteLogins:insecureLoginFormPresent": ["LoginManagerParent"],
-    // For Savant Shield study, bug 1465685. Study on desktop only.
-    "LoginStats:LoginFillSuccessful": ["LoginManagerParent"],
-    "LoginStats:LoginEncountered": ["LoginManagerParent"],
     // PLEASE KEEP THIS LIST IN SYNC WITH THE MOBILE LISTENERS IN BrowserCLH.js
     "WCCR:registerProtocolHandler": ["Feeds"],
     "rtcpeer:CancelRequest": ["webrtcUI"],
@@ -1400,8 +1396,6 @@ BrowserGlue.prototype = {
     }
 
     Normandy.uninit();
-
-    SavantShieldStudy.uninit();
   },
 
   // All initial windows have opened.
@@ -1558,10 +1552,6 @@ BrowserGlue.prototype = {
     Services.tm.idleDispatchToMainThread(() => {
       Blocklist.loadBlocklistAsync();
     });
-
-    Services.tm.idleDispatchToMainThread(() => {
-      SavantShieldStudy.init();
-    });
   },
 
   /**
diff --git a/browser/components/syncedtabs/sidebar.js b/browser/components/syncedtabs/sidebar.js
index bec9a4f1a5dc..32ec08c98ff8 100644
--- a/browser/components/syncedtabs/sidebar.js
+++ b/browser/components/syncedtabs/sidebar.js
@@ -7,18 +7,29 @@
 ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm");
 ChromeUtils.import("resource://services-sync/SyncedTabs.jsm");
 ChromeUtils.import("resource:///modules/syncedtabs/SyncedTabsDeckComponent.js");
+ChromeUtils.import("resource:///actors/LightweightThemeChild.jsm");
 
 ChromeUtils.defineModuleGetter(this, "fxAccounts",
                                "resource://gre/modules/FxAccounts.jsm");
 
 var syncedTabsDeckComponent = new SyncedTabsDeckComponent({window, SyncedTabs, fxAccounts});
 
+let themeListener;
+
 let onLoaded = () => {
+  themeListener = new LightweightThemeChild({
+    content: window,
+    chromeOuterWindowID: window.top.windowUtils.outerWindowID,
+    docShell: window.docShell,
+  });
   syncedTabsDeckComponent.init();
   document.getElementById("template-container").appendChild(syncedTabsDeckComponent.container);
 };
 
 let onUnloaded = () => {
+  if (themeListener) {
+    themeListener.cleanup();
+  }
   removeEventListener("DOMContentLoaded", onLoaded);
   removeEventListener("unload", onUnloaded);
   syncedTabsDeckComponent.uninit();
diff --git a/browser/components/syncedtabs/sidebar.xhtml b/browser/components/syncedtabs/sidebar.xhtml
index ef000cb46b93..a1198888fcea 100644
--- a/browser/components/syncedtabs/sidebar.xhtml
+++ b/browser/components/syncedtabs/sidebar.xhtml
@@ -19,6 +19,7 @@
   <head>
     <script src="chrome://browser/content/syncedtabs/sidebar.js" type="application/javascript"></script>
     <script type="application/javascript" src="chrome://browser/content/utilityOverlay.js"/>
+    <script src="chrome://browser/content/contentTheme.js"></script>
 
     <link rel="stylesheet" type="text/css" media="all" href="chrome://browser/skin/syncedtabs/sidebar.css"/>
     <link rel="stylesheet" type="text/css" media="all" href="chrome://global/skin/"/>
diff --git a/browser/components/translation/Translation.jsm b/browser/components/translation/Translation.jsm
index a1e1167fa926..1ea11f8fbe29 100644
--- a/browser/components/translation/Translation.jsm
+++ b/browser/components/translation/Translation.jsm
@@ -75,7 +75,7 @@ var Translation = {
   openProviderAttribution() {
     let attribution = this.supportedEngines[this.translationEngine];
     ChromeUtils.import("resource:///modules/BrowserWindowTracker.jsm");
-    BrowserWindowTracker.getTopWindow().openUILinkIn(attribution, "tab");
+    BrowserWindowTracker.getTopWindow().openWebLinkIn(attribution, "tab");
   },
 
   /**
diff --git a/browser/modules/BrowserUsageTelemetry.jsm b/browser/modules/BrowserUsageTelemetry.jsm
index bb8eafd837b6..4ccb46a835b7 100644
--- a/browser/modules/BrowserUsageTelemetry.jsm
+++ b/browser/modules/BrowserUsageTelemetry.jsm
@@ -366,10 +366,6 @@ let urlbarListener = {
       Services.telemetry
               .getKeyedHistogramById("FX_URLBAR_SELECTED_RESULT_INDEX_BY_TYPE")
               .add(actionType, idx);
-      if (actionType === "bookmark" || actionType === "history") {
-        Services.telemetry.recordEvent("savant", "follow_urlbar_link", actionType, null,
-                                      { subcategory: "navigation" });
-      }
     } else {
       Cu.reportError("Unknown FX_URLBAR_SELECTED_RESULT_TYPE type: " +
                      actionType);
@@ -503,9 +499,6 @@ let BrowserUsageTelemetry = {
                                       scalarKey, 1);
     Services.telemetry.recordEvent("navigation", "search", source, action,
                                    { engine: getSearchEngineId(engine) });
-    Services.telemetry.recordEvent("savant", "search", source, action,
-                                   { subcategory: "navigation",
-                                   engine: getSearchEngineId(engine) });
   },
 
   _handleSearchAction(engine, source, details) {
diff --git a/browser/modules/SavantShieldStudy.jsm b/browser/modules/SavantShieldStudy.jsm
deleted file mode 100644
index 9a29dae41a7c..000000000000
--- a/browser/modules/SavantShieldStudy.jsm
+++ /dev/null
@@ -1,530 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
-* License, v. 2.0. If a copy of the MPL was not distributed with this file,
-* You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-/* eslint semi: error */
-
-"use strict";
-
-var EXPORTED_SYMBOLS = ["SavantShieldStudy"];
-
-ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm");
-ChromeUtils.import("resource://gre/modules/Services.jsm");
-
-XPCOMUtils.defineLazyModuleGetters(this, {
-  AddonManager: "resource://gre/modules/AddonManager.jsm",
-  PlacesUtils: "resource://gre/modules/PlacesUtils.jsm"
-});
-
-// See LOG_LEVELS in Console.jsm. Examples: "all", "info", "warn", & "error".
-const PREF_LOG_LEVEL = "shield.savant.loglevel";
-
-// Create a new instance of the ConsoleAPI so we can control the maxLogLevel with a pref.
-XPCOMUtils.defineLazyGetter(this, "log", () => {
-  let ConsoleAPI = ChromeUtils.import("resource://gre/modules/Console.jsm", {}).ConsoleAPI;
-  let consoleOptions = {
-    maxLogLevelPref: PREF_LOG_LEVEL,
-    prefix: "SavantShieldStudy",
-  };
-  return new ConsoleAPI(consoleOptions);
-});
-
-class SavantShieldStudyClass {
-  constructor() {
-    this.STUDY_PREF = "shield.savant.enabled";
-    this.STUDY_TELEMETRY_CATEGORY = "savant";
-    this.ALWAYS_PRIVATE_BROWSING_PREF = "browser.privatebrowsing.autostart";
-    this.STUDY_DURATION_OVERRIDE_PREF = "shield.savant.duration_override";
-    this.STUDY_EXPIRATION_DATE_PREF = "shield.savant.expiration_date";
-    // ms = 'x' weeks * 7 days/week * 24 hours/day * 60 minutes/hour
-    // * 60 seconds/minute * 1000 milliseconds/second
-    this.DEFAULT_STUDY_DURATION_MS = 4 * 7 * 24 * 60 * 60 * 1000;
-    // If on startupStudy(), user is ineligible or study has expired,
-    // no probe listeners from this module have been added yet
-    this.shouldRemoveListeners = true;
-  }
-
-  init() {
-    this.telemetryEvents = new TelemetryEvents(this.STUDY_TELEMETRY_CATEGORY);
-    this.addonListener = new AddonListener(this.STUDY_TELEMETRY_CATEGORY);
-    this.bookmarkObserver = new BookmarkObserver(this.STUDY_TELEMETRY_CATEGORY);
-    this.menuListener = new MenuListener(this.STUDY_TELEMETRY_CATEGORY);
-
-    // check the pref in case Normandy flipped it on before we could add the pref listener
-    this.shouldCollect = Services.prefs.getBoolPref(this.STUDY_PREF);
-    if (this.shouldCollect) {
-      this.startupStudy();
-    }
-    Services.prefs.addObserver(this.STUDY_PREF, this);
-  }
-
-  observe(subject, topic, data) {
-    if (topic === "nsPref:changed" && data === this.STUDY_PREF) {
-      // toggle state of the pref
-      this.shouldCollect = !this.shouldCollect;
-      if (this.shouldCollect) {
-        this.startupStudy();
-      } else {
-        // The pref has been turned off
-        this.endStudy("study_disable");
-      }
-    }
-  }
-
-  startupStudy() {
-    // enable before any possible calls to endStudy, since it sends an 'end_study' event
-    this.telemetryEvents.enableCollection();
-
-    if (!this.isEligible()) {
-      this.shouldRemoveListeners = false;
-      this.endStudy("ineligible");
-      return;
-    }
-
-    this.initStudyDuration();
-
-    if (this.isStudyExpired()) {
-      log.debug("Study expired in between this and the previous session.");
-      this.shouldRemoveListeners = false;
-      this.endStudy("expired");
-    }
-
-    this.addonListener.init();
-    this.bookmarkObserver.init();
-    this.menuListener.init();
-  }
-
-  isEligible() {
-    const isAlwaysPrivateBrowsing = Services.prefs.getBoolPref(this.ALWAYS_PRIVATE_BROWSING_PREF);
-    if (isAlwaysPrivateBrowsing) {
-      return false;
-    }
-
-    return true;
-  }
-
-  initStudyDuration() {
-    if (Services.prefs.getStringPref(this.STUDY_EXPIRATION_DATE_PREF, "")) {
-      return;
-    }
-    Services.prefs.setStringPref(
-      this.STUDY_EXPIRATION_DATE_PREF,
-      this.getExpirationDateString()
-    );
-  }
-
-  getDurationFromPref() {
-    return Services.prefs.getIntPref(this.STUDY_DURATION_OVERRIDE_PREF, 0);
-  }
-
-  getExpirationDateString() {
-    const now = Date.now();
-    const studyDurationInMs =
-    this.getDurationFromPref()
-      || this.DEFAULT_STUDY_DURATION_MS;
-    const expirationDateInt = now + studyDurationInMs;
-    return new Date(expirationDateInt).toISOString();
-  }
-
-  isStudyExpired() {
-    const expirationDateInt =
-      Date.parse(Services.prefs.getStringPref(
-        this.STUDY_EXPIRATION_DATE_PREF,
-        this.getExpirationDateString()
-      ));
-
-    if (isNaN(expirationDateInt)) {
-      log.error(
-        `The value for the preference ${this.STUDY_EXPIRATION_DATE_PREF} is invalid.`
-      );
-      return false;
-    }
-
-    if (Date.now() > expirationDateInt) {
-      return true;
-    }
-    return false;
-  }
-
-  endStudy(reason) {
-    log.debug(`Ending the study due to reason: ${ reason }`);
-    const isStudyEnding = true;
-    Services.telemetry.recordEvent(this.STUDY_TELEMETRY_CATEGORY, "end_study", reason, null,
-                                  { subcategory: "shield" });
-    this.telemetryEvents.disableCollection();
-    this.uninit(isStudyEnding);
-    // These prefs needs to persist between restarts, so only reset on endStudy
-    Services.prefs.clearUserPref(this.STUDY_PREF);
-    Services.prefs.clearUserPref(this.STUDY_EXPIRATION_DATE_PREF);
-  }
-
-  // Called on every Firefox shutdown and endStudy
-  uninit(isStudyEnding = false) {
-    // if just shutting down, check for expiration, so the endStudy event can
-    // be sent along with this session's main ping.
-    if (!isStudyEnding && this.isStudyExpired()) {
-      log.debug("Study expired during this session.");
-      this.endStudy("expired");
-      return;
-    }
-
-    this.addonListener.uninit();
-    this.bookmarkObserver.uninit();
-    this.menuListener.uninit();
-
-    Services.prefs.removeObserver(this.ALWAYS_PRIVATE_BROWSING_PREF, this);
-    Services.prefs.removeObserver(this.STUDY_PREF, this);
-    Services.prefs.removeObserver(this.STUDY_DURATION_OVERRIDE_PREF, this);
-    Services.prefs.clearUserPref(PREF_LOG_LEVEL);
-    Services.prefs.clearUserPref(this.STUDY_DURATION_OVERRIDE_PREF);
-  }
-}
-
-// References:
-// - https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/normandy/lib/TelemetryEvents.jsm
-// - https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/normandy/lib/PreferenceExperiments.jsm#l357
-class TelemetryEvents {
-  constructor(studyCategory) {
-    this.STUDY_TELEMETRY_CATEGORY = studyCategory;
-  }
-
-  enableCollection() {
-    log.debug("Study has been enabled; turning ON data collection.");
-    Services.telemetry.setEventRecordingEnabled(this.STUDY_TELEMETRY_CATEGORY, true);
-  }
-
-  disableCollection() {
-    log.debug("Study has been disabled; turning OFF data collection.");
-    Services.telemetry.setEventRecordingEnabled(this.STUDY_TELEMETRY_CATEGORY, false);
-  }
-}
-
-class AddonListener {
-  constructor(studyCategory) {
-    this.STUDY_TELEMETRY_CATEGORY = studyCategory;
-    this.METHOD = "addon";
-    this.EXTRA_SUBCATEGORY = "customize";
-  }
-
-  init() {
-    this.listener = {
-      onInstalling: (addon, needsRestart) => {
-        const addon_id = addon.id;
-        this.recordEvent("install_start", addon_id);
-      },
-
-      onInstalled: (addon) => {
-        const addon_id = addon.id;
-        this.recordEvent("install_finish", addon_id);
-      },
-
-      onEnabled: (addon) => {
-        const addon_id = addon.id;
-        this.recordEvent("enable", addon_id);
-      },
-
-      onDisabled: (addon) => {
-        const addon_id = addon.id;
-        this.recordEvent("disable", addon_id);
-      },
-
-      onUninstalling: (addon, needsRestart) => {
-        const addon_id = addon.id;
-        this.recordEvent("remove_start", addon_id);
-      },
-
-      onUninstalled: (addon) => {
-        const addon_id = addon.id;
-        this.recordEvent("remove_finish", addon_id);
-      }
-    };
-    this.addListeners();
-  }
-
-  addListeners() {
-    AddonManager.addAddonListener(this.listener);
-  }
-
-  recordEvent(event, addon_id) {
-    log.debug(`Addon ID: ${addon_id}; event: ${ event }`);
-    Services.telemetry.recordEvent(this.STUDY_TELEMETRY_CATEGORY,
-                                  this.METHOD,
-                                  event,
-                                  addon_id,
-                                  { subcategory: this.EXTRA_SUBCATEGORY });
-  }
-
-  removeListeners() {
-    AddonManager.removeAddonListener(this.listener);
-  }
-
-  uninit() {
-    if (SavantShieldStudy.shouldRemoveListeners) {
-      this.removeListeners();
-    }
-  }
-}
-
-class BookmarkObserver {
-  constructor(studyCategory) {
-    this.STUDY_TELEMETRY_CATEGORY = studyCategory;
-    // there are two probes: bookmark and follow_bookmark
-    this.METHOD_1 = "bookmark";
-    this.EXTRA_SUBCATEGORY_1 = "feature";
-    this.METHOD_2 = "follow_bookmark";
-    this.EXTRA_SUBCATEGORY_2 = "navigation";
-    this.TYPE_BOOKMARK = Ci.nsINavBookmarksService.TYPE_BOOKMARK;
-    // Ignore "fake" bookmarks created for bookmark tags
-    this.skipTags = true;
-  }
-
-  init() {
-    this.addObservers();
-  }
-
-  addObservers() {
-    PlacesUtils.bookmarks.addObserver(this);
-  }
-
-  onItemAdded(itemID, parentID, index, itemType, uri, title, dateAdded, guid, parentGUID, source) {
-    this.handleItemAddRemove(itemType, uri, source, "save");
-  }
-
-  onItemRemoved(itemID, parentID, index, itemType, uri, guid, parentGUID, source) {
-    this.handleItemAddRemove(itemType, uri, source, "remove");
-  }
-
-  handleItemAddRemove(itemType, uri, source, event) {
-    /*
-    * "place:query" uris are used to create containers like Most Visited or
-    * Recently Bookmarked. These are added as default bookmarks.
-    */
-    if (itemType === this.TYPE_BOOKMARK && !uri.schemeIs("place")
-      && source === PlacesUtils.bookmarks.SOURCE_DEFAULT) {
-      const isBookmarkProbe = true;
-      this.recordEvent(event, isBookmarkProbe);
-    }
-  }
-
-  // This observer is only fired for TYPE_BOOKMARK items.
-  onItemVisited(itemID, visitID, time, transitionType, uri, parentID, guid, parentGUID) {
-    const isBookmarkProbe = false;
-    this.recordEvent("open", isBookmarkProbe);
-  }
-
-  recordEvent(event, isBookmarkProbe) {
-    const method = isBookmarkProbe ? this.METHOD_1 : this.METHOD_2;
-    const subcategory = isBookmarkProbe ? this.EXTRA_SUBCATEGORY_1 : this.EXTRA_SUBCATEGORY_2;
-    Services.telemetry.recordEvent(this.STUDY_TELEMETRY_CATEGORY, method, event, null,
-                                  {
-                                    subcategory
-                                  });
-  }
-
-  removeObservers() {
-    PlacesUtils.bookmarks.removeObserver(this);
-  }
-
-  uninit() {
-    if (SavantShieldStudy.shouldRemoveListeners) {
-      this.removeObservers();
-    }
-  }
-}
-
-class MenuListener {
-  constructor(studyCategory) {
-    this.STUDY_TELEMETRY_CATEGORY = studyCategory;
-    this.NAVIGATOR_TOOLBOX_ID = "navigator-toolbox";
-    this.OVERFLOW_PANEL_ID = "widget-overflow";
-    this.LIBRARY_PANELVIEW_ID = "appMenu-libraryView";
-    this.HAMBURGER_PANEL_ID = "appMenu-popup";
-    this.DOTDOTDOT_PANEL_ID = "pageActionPanel";
-    this.windowWatcher = new WindowWatcher();
-  }
-
-  init() {
-    this.windowWatcher.init(this.loadIntoWindow.bind(this),
-    this.unloadFromWindow.bind(this),
-    this.onWindowError.bind(this));
-  }
-
- loadIntoWindow(win) {
-    this.addListeners(win);
-  }
-
-  unloadFromWindow(win) {
-    this.removeListeners(win);
-  }
-
-  onWindowError(msg) {
-    log.error(msg);
-  }
-
-  addListeners(win) {
-    const doc = win.document;
-    const navToolbox = doc.getElementById(this.NAVIGATOR_TOOLBOX_ID);
-    const overflowPanel = doc.getElementById(this.OVERFLOW_PANEL_ID);
-    const hamburgerPanel = doc.getElementById(this.HAMBURGER_PANEL_ID);
-    const dotdotdotPanel = doc.getElementById(this.DOTDOTDOT_PANEL_ID);
-
-    /*
-    * the library menu "ViewShowing" event bubbles up on the navToolbox in its
-    * default location. A separate listener is needed if it is moved to the
-    * overflow panel via Hamburger > Customize
-    */
-    navToolbox.addEventListener("ViewShowing", this);
-    overflowPanel.addEventListener("ViewShowing", this);
-    hamburgerPanel.addEventListener("popupshown", this);
-    dotdotdotPanel.addEventListener("popupshown", this);
-  }
-
-  handleEvent(evt) {
-    switch (evt.type) {
-      case "ViewShowing":
-        if (evt.target.id === this.LIBRARY_PANELVIEW_ID) {
-          log.debug("Library panel opened.");
-          this.recordEvent("library_menu");
-        }
-        break;
-      case "popupshown":
-        switch (evt.target.id) {
-          case this.HAMBURGER_PANEL_ID:
-            log.debug("Hamburger panel opened.");
-            this.recordEvent("hamburger_menu");
-            break;
-          case this.DOTDOTDOT_PANEL_ID:
-            log.debug("Dotdotdot panel opened.");
-            this.recordEvent("dotdotdot_menu");
-            break;
-          default:
-            break;
-        }
-      break;
-    }
-  }
-
-  recordEvent(method) {
-    Services.telemetry.recordEvent(this.STUDY_TELEMETRY_CATEGORY, method, "open", null,
-                                  { subcategory: "menu" });
-  }
-
-  removeListeners(win) {
-    const doc = win.document;
-    const navToolbox = doc.getElementById(this.NAVIGATOR_TOOLBOX_ID);
-    const overflowPanel = doc.getElementById(this.OVERFLOW_PANEL_ID);
-    const hamburgerPanel = doc.getElementById(this.HAMBURGER_PANEL_ID);
-    const dotdotdotPanel = doc.getElementById(this.DOTDOTDOT_PANEL_ID);
-
-    try {
-      navToolbox.removeEventListener("ViewShowing", this);
-      overflowPanel.removeEventListener("ViewShowing", this);
-      hamburgerPanel.removeEventListener("popupshown", this);
-      dotdotdotPanel.removeEventListener("popupshown", this);
-    } catch (err) {
-      // Firefox is shutting down; elements have already been removed.
-    }
-  }
-
-  uninit() {
-    if (SavantShieldStudy.shouldRemoveListeners) {
-      this.windowWatcher.uninit();
-    }
-  }
-}
-
-/*
-* The WindowWatcher is used to add/remove listeners from MenuListener
-* to/from all windows.
-*/
-class WindowWatcher {
-  constructor() {
-    this._isActive = false;
-    this._loadCallback = null;
-    this._unloadCallback = null;
-    this._errorCallback = null;
-  }
-
-  // It is expected that loadCallback, unloadCallback, and errorCallback are bound
-  // to a `this` value.
-  init(loadCallback, unloadCallback, errorCallback) {
-    if (this._isActive) {
-      errorCallback("Called init, but WindowWatcher was already running");
-      return;
-    }
-
-    this._isActive = true;
-    this._loadCallback = loadCallback;
-    this._unloadCallback = unloadCallback;
-    this._errorCallback = errorCallback;
-
-    // Add loadCallback to existing windows
-    for (const win of Services.wm.getEnumerator("navigator:browser")) {
-      try {
-        this._loadCallback(win);
-      } catch (ex) {
-        this._errorCallback(`WindowWatcher code loading callback failed: ${ ex }`);
-      }
-    }
-
-    // Add loadCallback to future windows
-    // This will call the observe method on WindowWatcher
-    Services.ww.registerNotification(this);
-  }
-
-  uninit() {
-    if (!this._isActive) {
-      this._errorCallback("Called uninit, but WindowWatcher was already uninited");
-      return;
-    }
-
-    for (const win of Services.wm.getEnumerator("navigator:browser")) {
-      try {
-        this._unloadCallback(win);
-      } catch (ex) {
-        this._errorCallback(`WindowWatcher code unloading callback failed: ${ ex }`);
-      }
-    }
-
-    Services.ww.unregisterNotification(this);
-
-    this._loadCallback = null;
-    this._unloadCallback = null;
-    this._errorCallback = null;
-    this._isActive = false;
-  }
-
-  observe(win, topic) {
-    switch (topic) {
-      case "domwindowopened":
-        this._onWindowOpened(win);
-        break;
-      case "domwindowclosed":
-        this._onWindowClosed(win);
-        break;
-      default:
-        break;
-    }
-  }
-
-  _onWindowOpened(win) {
-    win.addEventListener("load", this, { once: true });
-  }
-
-  // only one event type expected: "load"
-  handleEvent(evt) {
-    const win = evt.target.ownerGlobal;
-
-    // make sure we only add window listeners to a DOMWindow (browser.xul)
-    const winType = win.document.documentElement.getAttribute("windowtype");
-    if (winType === "navigator:browser") {
-      this._loadCallback(win);
-    }
-  }
-
-  _onWindowClosed(win) {
-    this._unloadCallback(win);
-  }
-}
-
-const SavantShieldStudy = new SavantShieldStudyClass();
diff --git a/browser/modules/moz.build b/browser/modules/moz.build
index b7ffc0476c2c..46b68887419e 100644
--- a/browser/modules/moz.build
+++ b/browser/modules/moz.build
@@ -138,7 +138,6 @@ EXTRA_JS_MODULES += [
     'ReaderParent.jsm',
     'RemotePrompt.jsm',
     'Sanitizer.jsm',
-    'SavantShieldStudy.jsm',
     'SchedulePressure.jsm',
     'SiteDataManager.jsm',
     'SitePermissions.jsm',
diff --git a/browser/themes/osx/syncedtabs/sidebar.css b/browser/themes/osx/syncedtabs/sidebar.css
index a2b84831e347..f6f96bff03c4 100644
--- a/browser/themes/osx/syncedtabs/sidebar.css
+++ b/browser/themes/osx/syncedtabs/sidebar.css
@@ -6,7 +6,7 @@
 
 /* These styles are intended to mimic XUL trees and the XUL search box. */
 
-.content-container {
+body:not([lwt-sidebar]) .content-container {
   -moz-appearance: -moz-mac-source-list;
   -moz-font-smoothing-background-color: -moz-mac-source-list;
 }
diff --git a/browser/themes/shared/customizableui/panelUI.inc.css b/browser/themes/shared/customizableui/panelUI.inc.css
index 3c9624d51c8b..8fd2bdc42a02 100644
--- a/browser/themes/shared/customizableui/panelUI.inc.css
+++ b/browser/themes/shared/customizableui/panelUI.inc.css
@@ -871,6 +871,10 @@ panelview .toolbarbutton-1,
   outline: 0;
 }
 
+.subviewbutton[disabled="true"] {
+  color: var(--panel-disabled-color);
+}
+
 .subviewbutton > .toolbarbutton-text {
   padding: 0;
   padding-inline-start: 24px; /* This is 16px for the icon + 8px for the padding as defined below. */
diff --git a/browser/themes/shared/syncedtabs/sidebar.inc.css b/browser/themes/shared/syncedtabs/sidebar.inc.css
index 18d8bb90cab2..942e7727c6ad 100644
--- a/browser/themes/shared/syncedtabs/sidebar.inc.css
+++ b/browser/themes/shared/syncedtabs/sidebar.inc.css
@@ -69,7 +69,6 @@ body {
   white-space: nowrap;
   overflow: hidden;
   outline: none;
-  color: -moz-FieldText;
 }
 
 .item.selected > .item-title-container {
@@ -296,3 +295,26 @@ body {
 .filtered .textbox-search-icons .textbox-search-clear {
   display: block;
 }
+
+/* Themed sidebars */
+
+body[lwt-sidebar] {
+  background-color: var(--lwt-sidebar-background-color);
+  color: var(--lwt-sidebar-text-color);
+}
+
+body[lwt-sidebar] .item.selected > .item-title-container {
+  background-color: hsla(0,0%,80%,.3);
+  color: inherit;
+}
+
+body[lwt-sidebar-brighttext] .item.selected > .item-title-container {
+  -moz-appearance: none;
+  background-color: rgba(249,249,250,.1);
+}
+
+body[lwt-sidebar-highlight] .item.selected:focus > .item-title-container {
+  -moz-appearance: none;
+  background-color: var(--lwt-sidebar-highlight-background-color);
+  color: var(--lwt-sidebar-highlight-text-color);
+}
diff --git a/config/external/moz.build b/config/external/moz.build
index 21667e0543f8..86aa5351335a 100644
--- a/config/external/moz.build
+++ b/config/external/moz.build
@@ -8,12 +8,16 @@ external_dirs = []
 
 DIRS += [
     'lgpllibs',
-    'prio',
     'sqlite',
 ]
 if not CONFIG['MOZ_SYSTEM_JPEG']:
     external_dirs += ['media/libjpeg']
 
+if CONFIG['MOZ_LIBPRIO']:
+    DIRS += [
+        'prio',
+    ]
+
 # There's no "native" brotli or woff2 yet, but probably in the future...
 external_dirs += ['modules/brotli']
 external_dirs += ['modules/woff2']
diff --git a/config/external/msgpack/moz.build b/config/external/msgpack/moz.build
index 9e9599a8b228..3dc3955bf237 100644
--- a/config/external/msgpack/moz.build
+++ b/config/external/msgpack/moz.build
@@ -4,5 +4,6 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-DIRS += ['/third_party/msgpack']
+if CONFIG['MOZ_LIBPRIO']:
+    DIRS += ['/third_party/msgpack']
 
diff --git a/config/external/prio/moz.build b/config/external/prio/moz.build
index b8a167496189..df3540f8ef49 100644
--- a/config/external/prio/moz.build
+++ b/config/external/prio/moz.build
@@ -4,5 +4,5 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-DIRS += ['../../../third_party/prio']
+DIRS += ['/third_party/prio']
 
diff --git a/devtools/client/aboutdebugging-new/aboutdebugging.css b/devtools/client/aboutdebugging-new/aboutdebugging.css
index e677c486cb8f..77f4b73965bf 100644
--- a/devtools/client/aboutdebugging-new/aboutdebugging.css
+++ b/devtools/client/aboutdebugging-new/aboutdebugging.css
@@ -6,12 +6,12 @@
 @import "resource://devtools/client/aboutdebugging-new/src/components/App.css";
 @import "resource://devtools/client/aboutdebugging-new/src/components/ConnectPage.css";
 @import "resource://devtools/client/aboutdebugging-new/src/components/RuntimeInfo.css";
-@import "resource://devtools/client/aboutdebugging-new/src/components/Sidebar.css";
-@import "resource://devtools/client/aboutdebugging-new/src/components/SidebarItem.css";
 @import "resource://devtools/client/aboutdebugging-new/src/components/debugtarget/DebugTargetItem.css";
 @import "resource://devtools/client/aboutdebugging-new/src/components/debugtarget/DebugTargetList.css";
 @import "resource://devtools/client/aboutdebugging-new/src/components/debugtarget/ExtensionDetail.css";
 @import "resource://devtools/client/aboutdebugging-new/src/components/debugtarget/WorkerDetail.css";
+@import "resource://devtools/client/aboutdebugging-new/src/components/sidebar/Sidebar.css";
+@import "resource://devtools/client/aboutdebugging-new/src/components/sidebar/SidebarItem.css";
 
 :root {
   /* Import css variables from common.css */
diff --git a/devtools/client/aboutdebugging-new/src/components/App.js b/devtools/client/aboutdebugging-new/src/components/App.js
index a18ea556d3e8..62bfb505f664 100644
--- a/devtools/client/aboutdebugging-new/src/components/App.js
+++ b/devtools/client/aboutdebugging-new/src/components/App.js
@@ -13,7 +13,7 @@ const { PAGES } = require("../constants");
 
 const ConnectPage = createFactory(require("./ConnectPage"));
 const RuntimePage = createFactory(require("./RuntimePage"));
-const Sidebar = createFactory(require("./Sidebar"));
+const Sidebar = createFactory(require("./sidebar/Sidebar"));
 
 class App extends PureComponent {
   static get propTypes() {
diff --git a/devtools/client/aboutdebugging-new/src/components/ConnectPage.js b/devtools/client/aboutdebugging-new/src/components/ConnectPage.js
index 34ef10043498..65afee4b5184 100644
--- a/devtools/client/aboutdebugging-new/src/components/ConnectPage.js
+++ b/devtools/client/aboutdebugging-new/src/components/ConnectPage.js
@@ -142,8 +142,11 @@ class ConnectPage extends PureComponent {
         {
           className: "connect-page__network-form",
           onSubmit: (e) => {
-            addNetworkLocation(this.state.locationInputValue);
-            this.setState({ locationInputValue: "" });
+            const locationInputValue = this.state.locationInputValue;
+            if (locationInputValue) {
+              addNetworkLocation(locationInputValue);
+              this.setState({ locationInputValue: "" });
+            }
             e.preventDefault();
           }
         },
@@ -155,9 +158,7 @@ class ConnectPage extends PureComponent {
           value: this.state.locationInputValue,
           onChange: (e) => {
             const locationInputValue = e.target.value;
-            if (locationInputValue) {
-              this.setState({ locationInputValue });
-            }
+            this.setState({ locationInputValue });
           }
         }),
         dom.button({
diff --git a/devtools/client/aboutdebugging-new/src/components/moz.build b/devtools/client/aboutdebugging-new/src/components/moz.build
index b61217005c8c..36dc3baaccc3 100644
--- a/devtools/client/aboutdebugging-new/src/components/moz.build
+++ b/devtools/client/aboutdebugging-new/src/components/moz.build
@@ -4,6 +4,7 @@
 
 DIRS += [
     'debugtarget',
+    'sidebar',
 ]
 
 DevToolsModules(
@@ -14,8 +15,4 @@ DevToolsModules(
     'RuntimeInfo.css',
     'RuntimeInfo.js',
     'RuntimePage.js',
-    'Sidebar.css',
-    'Sidebar.js',
-    'SidebarItem.css',
-    'SidebarItem.js',
 )
diff --git a/devtools/client/aboutdebugging-new/src/components/Sidebar.css b/devtools/client/aboutdebugging-new/src/components/sidebar/Sidebar.css
similarity index 100%
rename from devtools/client/aboutdebugging-new/src/components/Sidebar.css
rename to devtools/client/aboutdebugging-new/src/components/sidebar/Sidebar.css
diff --git a/devtools/client/aboutdebugging-new/src/components/Sidebar.js b/devtools/client/aboutdebugging-new/src/components/sidebar/Sidebar.js
similarity index 97%
rename from devtools/client/aboutdebugging-new/src/components/Sidebar.js
rename to devtools/client/aboutdebugging-new/src/components/sidebar/Sidebar.js
index 1eb059a6490a..95904886d038 100644
--- a/devtools/client/aboutdebugging-new/src/components/Sidebar.js
+++ b/devtools/client/aboutdebugging-new/src/components/sidebar/Sidebar.js
@@ -8,7 +8,7 @@ const { createFactory, PureComponent } = require("devtools/client/shared/vendor/
 const dom = require("devtools/client/shared/vendor/react-dom-factories");
 const PropTypes = require("devtools/client/shared/vendor/react-prop-types");
 
-const { PAGES } = require("../constants");
+const { PAGES } = require("../../constants");
 
 const SidebarItem = createFactory(require("./SidebarItem"));
 const FIREFOX_ICON = "chrome://devtools/skin/images/aboutdebugging-firefox-logo.svg";
diff --git a/devtools/client/aboutdebugging-new/src/components/SidebarItem.css b/devtools/client/aboutdebugging-new/src/components/sidebar/SidebarItem.css
similarity index 100%
rename from devtools/client/aboutdebugging-new/src/components/SidebarItem.css
rename to devtools/client/aboutdebugging-new/src/components/sidebar/SidebarItem.css
diff --git a/devtools/client/aboutdebugging-new/src/components/SidebarItem.js b/devtools/client/aboutdebugging-new/src/components/sidebar/SidebarItem.js
similarity index 96%
rename from devtools/client/aboutdebugging-new/src/components/SidebarItem.js
rename to devtools/client/aboutdebugging-new/src/components/sidebar/SidebarItem.js
index 3edad77a2942..507797cb1997 100644
--- a/devtools/client/aboutdebugging-new/src/components/SidebarItem.js
+++ b/devtools/client/aboutdebugging-new/src/components/sidebar/SidebarItem.js
@@ -8,7 +8,7 @@ const { PureComponent } = require("devtools/client/shared/vendor/react");
 const dom = require("devtools/client/shared/vendor/react-dom-factories");
 const PropTypes = require("devtools/client/shared/vendor/react-prop-types");
 
-const Actions = require("../actions/index");
+const Actions = require("../../actions/index");
 
 /**
  * This component displays an item of the Sidebar component.
diff --git a/devtools/client/aboutdebugging-new/src/components/sidebar/moz.build b/devtools/client/aboutdebugging-new/src/components/sidebar/moz.build
new file mode 100644
index 000000000000..19f98e1aa794
--- /dev/null
+++ b/devtools/client/aboutdebugging-new/src/components/sidebar/moz.build
@@ -0,0 +1,10 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DevToolsModules(
+    'Sidebar.css',
+    'Sidebar.js',
+    'SidebarItem.css',
+    'SidebarItem.js',
+)
diff --git a/devtools/client/definitions.js b/devtools/client/definitions.js
index 5d317f77b6f2..67fd65b86d22 100644
--- a/devtools/client/definitions.js
+++ b/devtools/client/definitions.js
@@ -33,6 +33,7 @@ loader.lazyRequireGetter(this, "CommandUtils", "devtools/client/shared/developer
 loader.lazyRequireGetter(this, "CommandState", "devtools/shared/gcli/command-state", true);
 loader.lazyRequireGetter(this, "ResponsiveUIManager", "devtools/client/responsive.html/manager", true);
 loader.lazyImporter(this, "ScratchpadManager", "resource://devtools/client/scratchpad/scratchpad-manager.jsm");
+loader.lazyRequireGetter(this, "getScreenshotFront", "resource://devtools/shared/fronts/screenshot", true);
 
 const {MultiLocalizationHelper} = require("devtools/shared/l10n");
 const L10N = new MultiLocalizationHelper(
@@ -106,14 +107,6 @@ Tools.webConsole = {
   accesskey: l10n("webConsoleCmd.accesskey"),
   ordinal: 2,
   url: "chrome://devtools/content/webconsole/index.html",
-  get browserConsoleUsesHTML() {
-    return Services.prefs.getBoolPref("devtools.browserconsole.html");
-  },
-  get browserConsoleURL() {
-    return this.browserConsoleUsesHTML ?
-      "chrome://devtools/content/webconsole/index.html" :
-      "chrome://devtools/content/webconsole/browserconsole.xul";
-  },
   icon: "chrome://devtools/skin/images/tool-webconsole.svg",
   label: l10n("ToolboxTabWebconsole.label"),
   menuLabel: l10n("MenuWebconsole.label"),
@@ -594,16 +587,17 @@ exports.ToolboxButtons = [
   },
   { id: "command-button-screenshot",
     description: l10n("toolbox.buttons.screenshot"),
-    isTargetSupported: target => target.isLocalTab,
-    onClick(event, toolbox) {
+    isTargetSupported: target => !target.chrome && target.hasActor("screenshot"),
+    async onClick(event, toolbox) {
       // Special case for screenshot button to check for clipboard preference
       const clipboardEnabled = Services.prefs
         .getBoolPref("devtools.screenshot.clipboard.enabled");
-      let args = "--fullpage --file";
+      const args = { fullpage: true, file: true };
       if (clipboardEnabled) {
-        args += " --clipboard";
+        args.clipboard = true;
       }
-      CommandUtils.executeOnTarget(toolbox.target, "screenshot " + args);
+      const screenshotFront = getScreenshotFront(toolbox.target);
+      await screenshotFront.captureAndSave(toolbox.win, args);
     }
   },
   { id: "command-button-rulers",
diff --git a/devtools/client/inspector/fonts/components/FontPropertyValue.js b/devtools/client/inspector/fonts/components/FontPropertyValue.js
index 406a0de60f21..9ed94a1a3e0a 100644
--- a/devtools/client/inspector/fonts/components/FontPropertyValue.js
+++ b/devtools/client/inspector/fonts/components/FontPropertyValue.js
@@ -10,12 +10,12 @@ const PropTypes = require("devtools/client/shared/vendor/react-prop-types");
 const { KeyCodes } = require("devtools/client/shared/keycodes");
 
 // Milliseconds between auto-increment interval iterations.
-const AUTOINCREMENT_DELAY = 300;
+const AUTOINCREMENT_DELAY = 1000;
 
 class FontPropertyValue extends PureComponent {
   static get propTypes() {
     return {
-      allowAutoIncrement: PropTypes.bool,
+      autoIncrement: PropTypes.bool,
       className: PropTypes.string,
       defaultValue: PropTypes.oneOfType([ PropTypes.string, PropTypes.number ]),
       label: PropTypes.string.isRequired,
@@ -23,7 +23,7 @@ class FontPropertyValue extends PureComponent {
       max: PropTypes.number.isRequired,
       name: PropTypes.string.isRequired,
       onChange: PropTypes.func.isRequired,
-      step: PropTypes.oneOfType([ PropTypes.string, PropTypes.number ]),
+      step: PropTypes.number,
       unit: PropTypes.oneOfType([ PropTypes.string, null ]),
       unitOptions: PropTypes.array,
       value: PropTypes.number,
@@ -32,7 +32,9 @@ class FontPropertyValue extends PureComponent {
 
   static get defaultProps() {
     return {
+      autoIncrement: false,
       className: "",
+      step: 1,
       unitOptions: []
     };
   }
@@ -59,6 +61,7 @@ class FontPropertyValue extends PureComponent {
     this.onKeyDown = this.onKeyDown.bind(this);
     this.onKeyUp = this.onKeyUp.bind(this);
     this.onMouseDown = this.onMouseDown.bind(this);
+    this.onMouseMove = this.onMouseMove.bind(this);
     this.onMouseUp = this.onMouseUp.bind(this);
     this.onUnitChange = this.onUnitChange.bind(this);
     this.stopAutoIncrement = this.stopAutoIncrement.bind(this);
@@ -100,7 +103,7 @@ class FontPropertyValue extends PureComponent {
   /**
    * Check if the given value is valid according to the constraints of this component.
    * Ensure it is a number and that it does not go outside the min/max limits, unless
-   * allowed by the `allowAutoIncrement` props flag.
+   * allowed by the `autoIncrement` props flag.
    *
    * @param  {Number} value
    *         Numeric value
@@ -108,7 +111,7 @@ class FontPropertyValue extends PureComponent {
    *         Whether the value conforms to the components contraints.
    */
   isValueValid(value) {
-    const { allowAutoIncrement, min, max } = this.props;
+    const { autoIncrement, min, max } = this.props;
 
     if (typeof value !== "number" || isNaN(value)) {
       return false;
@@ -119,7 +122,7 @@ class FontPropertyValue extends PureComponent {
     }
 
     // Ensure it does not exceed maximum value, unless auto-incrementing is permitted.
-    if (max !== undefined && value > this.props.max && !allowAutoIncrement) {
+    if (max !== undefined && value > this.props.max && !autoIncrement) {
       return false;
     }
 
@@ -243,29 +246,33 @@ class FontPropertyValue extends PureComponent {
     });
   }
 
-  /**
-   * Handler for "keydown" events from the sider and input fields.
-   * Toggles on the "interactive" state. @See toggleInteractiveState();
-   * Begins auto-incrementing if the value is already at the upper bound.
-   *
-   * @param {Event} e
-   *        MouseDown event.
-   */
-  onMouseDown(e) {
-    // Begin auto-incrementing if the value is already at the upper bound.
-    if (this.isAtUpperBound(this.props.value) && e.target.type === "range") {
-      this.startAutoIncrement();
-    }
+  onMouseDown() {
     this.toggleInteractiveState(true);
   }
 
-  onMouseUp(e) {
+  /**
+   * Handler for "mousemove" event from range input. If the user is actively interacting
+   * by dragging the slider thumb, start or stop the auto-incrementing behavior depending
+   * on whether the input value is at the upper bound or not.
+   *
+   * @param {MouseEvent} e
+   */
+  onMouseMove(e) {
+    if (this.state.interactive && e.buttons) {
+      this.isAtUpperBound(this.props.value)
+        ? this.startAutoIncrement()
+        : this.stopAutoIncrement();
+    }
+  }
+
+  onMouseUp() {
+    this.stopAutoIncrement();
     this.toggleInteractiveState(false);
   }
 
   startAutoIncrement() {
     // Do not set auto-increment interval if not allowed to or if one is already set.
-    if (!this.props.allowAutoIncrement || this.interval) {
+    if (!this.props.autoIncrement || this.interval) {
       return;
     }
 
@@ -360,7 +367,7 @@ class FontPropertyValue extends PureComponent {
       onBlur: this.onBlur,
       onChange: this.onChange,
       onFocus: this.onFocus,
-      step: this.props.step || 1,
+      step: this.props.step,
       // While interacting with the range and number inputs, prevent updating value from
       // outside props which is debounced and causes jitter on successive renders.
       value: this.state.interactive
@@ -374,6 +381,7 @@ class FontPropertyValue extends PureComponent {
         onKeyDown: this.onKeyDown,
         onKeyUp: this.onKeyUp,
         onMouseDown: this.onMouseDown,
+        onMouseMove: this.onMouseMove,
         onMouseUp: this.onMouseUp,
         className: "font-value-slider",
         name: this.props.name,
@@ -386,7 +394,7 @@ class FontPropertyValue extends PureComponent {
       {
         ...defaults,
         // Remove upper limit from number input if it is allowed to auto-increment.
-        max: this.props.allowAutoIncrement ? null : this.props.max,
+        max: this.props.autoIncrement ? null : this.props.max,
         name: this.props.name,
         className: "font-value-input",
         type: "number",
diff --git a/devtools/client/inspector/fonts/components/FontSize.js b/devtools/client/inspector/fonts/components/FontSize.js
index bb3e4897130d..ca73802f8a16 100644
--- a/devtools/client/inspector/fonts/components/FontSize.js
+++ b/devtools/client/inspector/fonts/components/FontSize.js
@@ -58,7 +58,7 @@ class FontSize extends PureComponent {
       : max;
 
     return FontPropertyValue({
-      allowAutoIncrement: true,
+      autoIncrement: true,
       label: getStr("fontinspector.fontSizeLabel"),
       min: 0,
       max: this.historicMax[unit],
diff --git a/devtools/client/inspector/fonts/components/LineHeight.js b/devtools/client/inspector/fonts/components/LineHeight.js
index 022e43640668..239783fca38f 100644
--- a/devtools/client/inspector/fonts/components/LineHeight.js
+++ b/devtools/client/inspector/fonts/components/LineHeight.js
@@ -61,7 +61,7 @@ class LineHeight extends PureComponent {
       : max;
 
     return FontPropertyValue({
-      allowAutoIncrement: true,
+      autoIncrement: true,
       label: getStr("fontinspector.lineHeightLabel"),
       min: 0,
       max: this.historicMax[unit],
diff --git a/devtools/client/inspector/inspector.js b/devtools/client/inspector/inspector.js
index 612713ef9fbe..0c1713ce7574 100644
--- a/devtools/client/inspector/inspector.js
+++ b/devtools/client/inspector/inspector.js
@@ -33,9 +33,10 @@ loader.lazyRequireGetter(this, "nodeConstants", "devtools/shared/dom-node-consta
 loader.lazyRequireGetter(this, "Menu", "devtools/client/framework/menu");
 loader.lazyRequireGetter(this, "MenuItem", "devtools/client/framework/menu-item");
 loader.lazyRequireGetter(this, "ExtensionSidebar", "devtools/client/inspector/extensions/extension-sidebar");
-loader.lazyRequireGetter(this, "CommandUtils", "devtools/client/shared/developer-toolbar", true);
 loader.lazyRequireGetter(this, "clipboardHelper", "devtools/shared/platform/clipboard");
 loader.lazyRequireGetter(this, "openContentLink", "devtools/client/shared/link", true);
+loader.lazyRequireGetter(this, "getScreenshotFront", "devtools/shared/fronts/screenshot", true);
+loader.lazyRequireGetter(this, "saveScreenshot", "devtools/shared/screenshot/save");
 
 loader.lazyImporter(this, "DeferredTask", "resource://gre/modules/DeferredTask.jsm");
 
@@ -2318,21 +2319,22 @@ Inspector.prototype = {
    * Initiate gcli screenshot command on selected node.
    */
   async screenshotNode() {
-    const command = Services.prefs.getBoolPref("devtools.screenshot.clipboard.enabled") ?
-      "screenshot --file --clipboard --selector" :
-      "screenshot --file --selector";
-
     // Bug 1332936 - it's possible to call `screenshotNode` while the BoxModel highlighter
     // is still visible, therefore showing it in the picture.
     // To avoid that, we have to hide it before taking the screenshot. The `hideBoxModel`
     // will do that, calling `hide` for the highlighter only if previously shown.
     await this.highlighter.hideBoxModel();
 
-    // Bug 1180314 -  CssSelector might contain white space so need to make sure it is
-    // passed to screenshot as a single parameter.  More work *might* be needed if
-    // CssSelector could contain escaped single- or double-quotes, backslashes, etc.
-    CommandUtils.executeOnTarget(this._target,
-      `${command} '${this.selectionCssSelector}'`);
+    const clipboardEnabled = Services.prefs
+      .getBoolPref("devtools.screenshot.clipboard.enabled");
+    const args = {
+      file: true,
+      selector: this.selectionCssSelector,
+      clipboard: clipboardEnabled
+    };
+    const screenshotFront = getScreenshotFront(this.target);
+    const screenshot = await screenshotFront.capture(args);
+    await saveScreenshot(this.panelWin, args, screenshot);
   },
 
   /**
diff --git a/devtools/client/jar.mn b/devtools/client/jar.mn
index a04e46e51a81..e2aed8ff265b 100644
--- a/devtools/client/jar.mn
+++ b/devtools/client/jar.mn
@@ -149,7 +149,6 @@ devtools.jar:
     skin/images/editor-error.png (themes/images/editor-error.png)
     skin/images/breakpoint.svg (themes/images/breakpoint.svg)
     skin/webconsole.css (themes/webconsole.css)
-    skin/images/webconsole.svg (themes/images/webconsole.svg)
     skin/images/webconsole/alert.svg (themes/images/webconsole/alert.svg)
     skin/images/webconsole/info.svg (themes/images/webconsole/info.svg)
     skin/images/webconsole/input.svg (themes/images/webconsole/input.svg)
diff --git a/devtools/client/preferences/devtools-client.js b/devtools/client/preferences/devtools-client.js
index 1573ad03bd9b..0277a031041b 100644
--- a/devtools/client/preferences/devtools-client.js
+++ b/devtools/client/preferences/devtools-client.js
@@ -64,7 +64,7 @@ pref("devtools.new-animationinspector.enabled", true);
 // Enable the Font Editor
 pref("devtools.inspector.fonteditor.enabled", true);
 // Enable the font highlight-on-hover feature
-pref("devtools.inspector.fonthighlighter.enabled", false);
+pref("devtools.inspector.fonthighlighter.enabled", true);
 
 // Flexbox preferences
 // Enable the Flexbox highlighter in Nightly
diff --git a/devtools/client/shared/components/reps/reps.js b/devtools/client/shared/components/reps/reps.js
index b6d968c4db7e..5c8e5c85149f 100644
--- a/devtools/client/shared/components/reps/reps.js
+++ b/devtools/client/shared/components/reps/reps.js
@@ -4465,7 +4465,17 @@ class Tree extends Component {
         if (focused || !nativeEvent || !this.treeRef) {
           return;
         }
-        this._focus(traversal[0].item);
+
+        const { explicitOriginalTarget } = nativeEvent;
+        // Only set default focus to the first tree node if the focus came
+        // from outside the tree (e.g. by tabbing to the tree from other
+        // external elements).
+        if (
+          explicitOriginalTarget !== this.treeRef &&
+          !this.treeRef.contains(explicitOriginalTarget)
+        ) {
+          this._focus(traversal[0].item);
+        }
       },
       onBlur: this._onBlur,
       "aria-label": this.props.label,
diff --git a/devtools/client/themes/debugger.css b/devtools/client/themes/debugger.css
index fc2fff8fb3d7..84a2d97b091c 100644
--- a/devtools/client/themes/debugger.css
+++ b/devtools/client/themes/debugger.css
@@ -31,16 +31,17 @@
 
 .dbg-wasm-item .icon {
   display: block;
-  background-image: url(chrome://devtools/skin/images/webconsole.svg);
-  background-repeat: no-repeat;
-  background-size: 72px 60px;
-  /* show warning icon */
-  background-position: -24px -24px;
   width: 10px;
   height: 10px;
   position: absolute;
   margin-inline-start: -15px;
   margin-top: 3px;
+  /* show warning icon */
+  background-image: var(--theme-console-alert-image);
+  background-repeat: no-repeat;
+  background-size: contain;
+  -moz-context-properties: fill;
+  fill: #ec8633;
 }
 
 .dbg-breakpoint-line {
diff --git a/devtools/client/themes/images/webconsole.svg b/devtools/client/themes/images/webconsole.svg
deleted file mode 100644
index 6c21e549e904..000000000000
--- a/devtools/client/themes/images/webconsole.svg
+++ /dev/null
@@ -1,101 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<!-- This Source Code Form is subject to the terms of the Mozilla Public
-   - License, v. 2.0. If a copy of the MPL was not distributed with this
-   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
-<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="72" height="60" viewBox="0 0 72 60">
-  <defs>
-    <rect id="glyphShape-colorSwatch" width="8" height="8" ry="2" rx="2"/>
-    <rect id="glyphShape-colorSwatch-border" width="10" height="10" ry="2" rx="2"/>
-    <polygon id="glyphShape-errorX" points="9.9,8.5 8.5,9.9 6,7.4 3.6,9.8 2.2,8.4 4.6,6 2.2,3.6 3.6,2.2 6,4.6 8.4,2.2 9.8,3.6 7.4,6"/>
-    <path id="glyphShape-warningTriangle" d="M9.9,8.6l-3.1-6C6.6,2.2,6.3,2,6,2C5.7,2,5.4,2.2,5.2,2.5l-3.1,6C2,8.9,2,9.3,2.1,9.6C2.3,9.8,2.6,10,2.9,10 h6.1c0.4,0,0.6-0.2,0.8-0.4C10,9.3,10,8.9,9.9,8.6z"/>
-    <path id="glyphShape-exclamationPoint" d="M6,7.7c-0.6,0-1,0.4-1,0.8C5,9,5.4,9.3,6,9.3c0.6,0,1-0.4,1-0.8 C7,8.1,6.6,7.7,6,7.7z M6,7c0.6,0,1-0.4,1-1V5c0-0.6-0.4-1-1-1S5,4.4,5,5v1C5,6.6,5.4,7,6,7z"/>
-    <circle id="glyphShape-infoCircle" cx="6" cy="6" r="4"/>
-    <path id="glyphShape-infoGlyph" d="M6,6C5.4,6,5,6.4,5,7v1c0,0.6,0.4,1,1,1s1-0.4,1-1V7C7,6.4,6.6,6,6,6z M6,5c0.6,0,1-0.4,1-1S6.6,3,6,3S5,3.4,5,4S5.4,5,6,5z"/>
-    <style>
-      .icon-colorSwatch-border {
-        fill: #fff;
-        fill-opacity: .7;
-      }
-      .icon-colorSwatch-network {
-        fill: #000;
-      }
-      .icon-colorSwatch-css {
-        fill: #00b6f0;
-      }
-      .icon-colorSwatch-js {
-        fill: #fb9500;
-      }
-      .icon-colorSwatch-logging {
-        fill: #808080;
-      }
-      .icon-colorSwatch-security {
-        fill: #ec1e0d;
-      }
-      .icon-glyphOverlay {
-        fill: #fff;
-      }
-
-      #icon-indicator-input {
-        fill: #8fa1b2;
-      }
-      #icon-indicator-output {
-        fill: #667380;
-      }
-      #light-icons:target #icon-indicator-input {
-        fill: #45494d;
-      }
-      #light-icons:target #icon-indicator-output {
-        fill: #8a9199;
-      }
-    </style>
-  </defs>
-  <g id="icon-colorSwatch-network">
-    <use xlink:href="#glyphShape-colorSwatch-border" class="icon-colorSwatch-border" x="1" y="1"/>
-    <use xlink:href="#glyphShape-colorSwatch" class="icon-colorSwatch-network" x="2" y="2"/>
-  </g>
-  <g id="icon-colorSwatch-css" transform="translate(0 12)">
-    <use xlink:href="#glyphShape-colorSwatch-border" class="icon-colorSwatch-border" x="1" y="1"/>
-    <use xlink:href="#glyphShape-colorSwatch" class="icon-colorSwatch-css" x="2" y="2"/>
-  </g>
-  <g id="icon-colorSwatch-js" transform="translate(0 24)">
-    <use xlink:href="#glyphShape-colorSwatch-border" class="icon-colorSwatch-border" x="1" y="1"/>
-    <use xlink:href="#glyphShape-colorSwatch" class="icon-colorSwatch-js" x="2" y="2"/>
-  </g>
-  <g id="icon-colorSwatch-logging" transform="translate(0 36)">
-    <use xlink:href="#glyphShape-colorSwatch-border" class="icon-colorSwatch-border" x="1" y="1"/>
-    <use xlink:href="#glyphShape-colorSwatch" class="icon-colorSwatch-logging" x="2" y="2"/>
-  </g>
-  <g id="icon-colorSwatch-security" transform="translate(0 48)">
-    <use xlink:href="#glyphShape-colorSwatch-border" class="icon-colorSwatch-border" x="1" y="1"/>
-    <use xlink:href="#glyphShape-colorSwatch" class="icon-colorSwatch-security" x="2" y="2"/>
-  </g>
-  <use xlink:href="#glyphShape-errorX" id="icon-errorX-network" class="icon-colorSwatch-network" transform="translate(12)"/>
-  <use xlink:href="#glyphShape-errorX" id="icon-errorX-css" class="icon-colorSwatch-css" transform="translate(12 12)"/>
-  <use xlink:href="#glyphShape-errorX" id="icon-errorX-js" class="icon-colorSwatch-js" transform="translate(12 24)"/>
-  <use xlink:href="#glyphShape-errorX" id="icon-errorX-logging" class="icon-colorSwatch-logging" transform="translate(12 36)"/>
-  <use xlink:href="#glyphShape-errorX" id="icon-errorX-security" class="icon-colorSwatch-security" transform="translate(12 48)"/>
-  <g id="icon-warningTriangle-css" transform="translate(24 12)">
-    <use xlink:href="#glyphShape-warningTriangle" class="icon-colorSwatch-css"/>
-    <use xlink:href="#glyphShape-exclamationPoint" class="icon-glyphOverlay"/>
-  </g>
-  <g id="icon-warningTriangle-js" transform="translate(24 24)">
-    <use xlink:href="#glyphShape-warningTriangle" class="icon-colorSwatch-js"/>
-    <use xlink:href="#glyphShape-exclamationPoint" class="icon-glyphOverlay"/>
-  </g>
-  <g id="icon-warningTriangle-logging" transform="translate(24 36)">
-    <use xlink:href="#glyphShape-warningTriangle" class="icon-colorSwatch-logging"/>
-    <use xlink:href="#glyphShape-exclamationPoint" class="icon-glyphOverlay"/>
-  </g>
-  <g id="icon-warningTriangle-security" transform="translate(24 48)">
-    <use xlink:href="#glyphShape-warningTriangle" class="icon-colorSwatch-security"/>
-    <use xlink:href="#glyphShape-exclamationPoint" class="icon-glyphOverlay"/>
-  </g>
-  <g id="icon-infoCircle-logging" transform="translate(36 36)">
-    <use xlink:href="#glyphShape-infoCircle" class="icon-colorSwatch-logging"/>
-    <use xlink:href="#glyphShape-infoGlyph" class="icon-glyphOverlay"/>
-  </g>
-  <g id="light-icons">
-    <path id="icon-indicator-input" d="M6.5,1.2L5.4,2.3L9,6L5.3,9.7l1.1,1.1L11,6L6.5,1.2z M1.5,1.2 L0.4,2.3L4,6L0.3,9.7l1.1,1.1L6,6L1.5,1.2z" transform="translate(48 36)"/>
-    <polygon id="icon-indicator-output" points="10,5 4.3,5 6.8,2.4 5.5,1.2 1,6 5.5,10.8 6.9,9.6 4.3,7 10,7" transform="translate(60 36)"/>
-  </g>
-</svg>
\ No newline at end of file
diff --git a/devtools/client/themes/images/webconsole/alert.svg b/devtools/client/themes/images/webconsole/alert.svg
index 972bd6e5ce16..a3f98f97a4ed 100644
--- a/devtools/client/themes/images/webconsole/alert.svg
+++ b/devtools/client/themes/images/webconsole/alert.svg
@@ -3,5 +3,5 @@
    - License, v. 2.0. If a copy of the MPL was not distributed with this
    - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 12 12" fill="context-fill #0b0b0b">
-  <path d="M1.12 9.4L5 1.6c.41-.81 1.58-.81 2 0l3.88 7.78a1.11 1.11 0 0 1-1 1.61H2.11a1.11 1.11 0 0 1-1-1.6zM6 8.4c-.55 0-1 .4-1 .9s.45.9 1 .9 1-.4 1-.9-.45-.9-1-.9zm0-4.9c-.55 0-1 .36-1 .8v2.4c0 .44.45.8 1 .8s1-.36 1-.8V4.3c0-.44-.45-.8-1-.8z"/>
+  <path d="M1.12 9.4L5 1.6c.41-.81 1.58-.81 2 0l3.88 7.78a1.11 1.11 0 0 1-1 1.61H2.11a1.11 1.11 0 0 1-1-1.6zM6 7.8a1 1 0 1 0 0 2 1 1 0 0 0 0-2zm0-4.4a1 1 0 0 0-1 1V6a1 1 0 1 0 2 0V4.4a1 1 0 0 0-1-1z" />
 </svg>
diff --git a/devtools/client/themes/images/webconsole/info.svg b/devtools/client/themes/images/webconsole/info.svg
index 28827fdeff62..f3ad2bcdf394 100644
--- a/devtools/client/themes/images/webconsole/info.svg
+++ b/devtools/client/themes/images/webconsole/info.svg
@@ -3,5 +3,5 @@
    - License, v. 2.0. If a copy of the MPL was not distributed with this
    - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 12 12" fill="context-fill #0b0b0b">
-  <path d="M6 1a5 5 0 1 1 0 10A5 5 0 0 1 6 1zm0 1.5a1 1 0 1 1 0 2 1 1 0 0 1 0-2zm0 3c.55 0 1 .36 1 .8v2.4c0 .44-.45.8-1 .8s-1-.36-1-.8V6.3c0-.44.45-.8 1-.8z" fill-rule="evenodd"/>
+  <path d="M6 1a5 5 0 1 1 0 10A5 5 0 0 1 6 1zm0 1.6a1 1 0 1 0 0 2 1 1 0 0 0 0-2zm0 2.8a1 1 0 0 0-1 1V8a1 1 0 1 0 2 0V6.4a1 1 0 0 0-1-1z"/>
 </svg>
diff --git a/devtools/client/themes/jit-optimizations.css b/devtools/client/themes/jit-optimizations.css
index 363810504859..7266d26e136b 100644
--- a/devtools/client/themes/jit-optimizations.css
+++ b/devtools/client/themes/jit-optimizations.css
@@ -75,31 +75,24 @@
   color: var(--theme-highlight-red);
 }
 
-.theme-dark .opt-icon::before {
-  background-image: url(chrome://devtools/skin/images/webconsole.svg);
-}
-.theme-light .opt-icon::before {
-  background-image: url(chrome://devtools/skin/images/webconsole.svg#light-icons);
-}
-
 .opt-icon::before {
-  display: inline-block;
   content: "";
-  background-repeat: no-repeat;
-  background-size: 72px 60px;
-  /* show grey "i" bubble by default */
-  background-position: -36px -36px;
-  width: 10px;
-  height: 10px;
+  display: inline-block;
+  vertical-align: -2px;
+  width: 12px;
+  height: 12px;
   max-height: 12px;
-}
-
-.opt-icon::before {
-  margin: 1px 6px 0 0;
+  margin-inline-end: 5px;
+  background-image: var(--theme-console-info-image);
+  background-repeat: no-repeat;
+  background-size: contain;
+  -moz-context-properties: fill;
+  fill: #808080;
 }
 
 .opt-icon.warning::before {
-  background-position: -24px -24px;
+  background-image: var(--theme-console-alert-image);
+  fill: #ec8633;
 }
 
 /* Frame Component */
diff --git a/devtools/client/themes/memory.css b/devtools/client/themes/memory.css
index 525634264259..90e0645ebab5 100644
--- a/devtools/client/themes/memory.css
+++ b/devtools/client/themes/memory.css
@@ -557,20 +557,16 @@ html, body, #app, #memory-tool {
 .error::before {
   content: "";
   display: inline-block;
+  vertical-align: -2px;
   width: 12px;
   height: 12px;
   max-height: 12px;
-  background-image: url(chrome://devtools/skin/images/webconsole.svg);
-  background-size: 72px 60px;
-  background-position: -24px -24px;
-  background-repeat: no-repeat;
-  margin: 0px;
-  margin-top: 2px;
   margin-inline-end: 5px;
-}
-
-.theme-light .error::before {
-  background-image: url(chrome://devtools/skin/images/webconsole.svg#light-icons);
+  background-image: var(--theme-console-alert-image);
+  background-repeat: no-repeat;
+  background-size: contain;
+  -moz-context-properties: fill;
+  fill: #ec8633;
 }
 
 /**
diff --git a/devtools/client/themes/performance.css b/devtools/client/themes/performance.css
index fcd3949a835e..cb162b53d3b0 100644
--- a/devtools/client/themes/performance.css
+++ b/devtools/client/themes/performance.css
@@ -761,19 +761,17 @@ menuitem.marker-color-graphs-grey .menu-iconic-left::after,
  */
 menuitem.experimental-option::before {
   content: "";
-  background-image: url(chrome://devtools/skin/images/webconsole.svg);
-  background-repeat: no-repeat;
-  background-size: 72px 60px;
+  display: inline-block;
   width: 12px;
   height: 12px;
-  display: inline-block;
-
-  background-position: -24px -24px;
-  margin: 2px 5px 0 0;
   max-height: 12px;
-}
-.theme-light menuitem.experimental-option::before {
-  background-image: url(chrome://devtools/skin/images/webconsole.svg#light-icons);
+  margin-top: 2px;
+  margin-inline-end: 5px;
+  background-image: var(--theme-console-alert-image);
+  background-repeat: no-repeat;
+  background-size: contain;
+  -moz-context-properties: fill;
+  fill: currentColor;
 }
 
 #performance-options-menupopup:not(.experimental-enabled) .experimental-option,
diff --git a/devtools/client/themes/webconsole.css b/devtools/client/themes/webconsole.css
index c5a3265be29c..5c6bb9bfec8d 100644
--- a/devtools/client/themes/webconsole.css
+++ b/devtools/client/themes/webconsole.css
@@ -285,15 +285,18 @@ a {
   white-space: nowrap;
   overflow: hidden;
   text-overflow: ellipsis;
+  cursor: default;
 }
 
 .message.network .status {
   flex: none;
   margin-inline-start: 6px;
+  cursor: default;
 }
 
 .message.network.mixed-content .url {
   color: var(--theme-highlight-red);
+  cursor: default;
 }
 
 .message .learn-more-link {
diff --git a/devtools/client/webconsole/README.md b/devtools/client/webconsole/README.md
index aa320ff24dc0..54232c863581 100644
--- a/devtools/client/webconsole/README.md
+++ b/devtools/client/webconsole/README.md
@@ -6,125 +6,39 @@ It can also display network logs, and you can evaluate expressions using the con
 input, a.k.a. JsTerm. You can read more about it on [MDN](https://developer.mozilla.org/en-US/docs/Tools/Web_Console)
 to learn all the features and how to use the tool.
 
-## Old / New frontend
-
-The current console used in the toolbox is called the new frontend, and the code lives at
-the root of the `devtools/client/webconsole/` folder.
-The old console code is located in the `devtools/client/webconsole/old` folder.
-Both frontends use the same code for the console input, also called JsTerm (see `jsterm.js`).
-The old frontend is still used for the Browser Console, but is planned to be removed in the
-near future (see Bug 1381834).
-
-## Run WebConsole in DevTools panel
+## Run WebConsole
 
 If you want to build the WebConsole inside of the DevTools toolbox (Firefox Devtools Panels),
 follow the [simple Firefox build](http://docs.firefox-dev.tools/getting-started/build.html)
-document in MDN. Start your compiled firefox and open the Firefox developer tool, you can
+documentation. Start your compiled firefox and open the Firefox developer tool, you can
 then see the WebConsole tab.
 
-## Run WebConsole in a browser tab (experimental)
-
-### Prerequisite
-
-If you would like to run the WebConsole in the browser tab, you need following packages:
-
-* [node](https://nodejs.org/) >= 7.10.0 JavaScript runtime.
-* [yarn](https://yarnpkg.com/docs/install) >= 1.0.0 the package dependency management tool.
-* [Firefox](https://www.mozilla.org/firefox/new/) any version or build from the source code.
-
-### Run WebConsole
-
-Navigate to the `mozilla-central/devtools/client/webconsole` folder with your terminal.
-Note that this folder is available after `mozilla-central` was cloned in order to get a
-local copy of the repository. Then run the following commands:
-
-```bash
-# Install packages
-yarn install
-
-# Create a dev server instance for hosting webconsole on browser
-yarn start
-```
-
-Open `localhost:8000` to see what we call the [launchpad](https://github.com/devtools-html/devtools-core/tree/master/packages/devtools-launchpad).
-The UI that let you start a new Firefox window which will be the target (or debuggee).
-Launchpad will communicate with Firefox (the remote debugging server) and list all opened tabs from Firefox.
-You can then navigate to a website you want in the target window, and you should see it appears
-in the `localhost:8000` page. Clicking on it will start the WebConsole in the browser tab.
-
-### How it works
-
-The WebConsole uses [webpack](https://webpack.js.org/) and several packages from [devtools-core](https://github.com/devtools-html/devtools-core)
-to run as a normal web page. The WebConsole uses [Mozilla remote debugging protocol](http://searchfox.org/mozilla-central/source/devtools/docs/backend/protocol.md)
-to fetch messages and execute commands against Firefox.
-
-Open `localhost:8000` in any browser to see the
-interface. Devtools Launchpad will communicate with Firefox (the remote debugging server)
-and list all opened tabs from Firefox. Click one of the browser tab entry, now you can see
-the WebConsole runs in a browser tab.
-
-### DevTools shared modules
-
-When working on console running via launchpad, you may need to modify code on external modules.
-Besides the third party modules, here are modules required for the WebConsole
-(hosted under the `devtools-core` Github repo, which contains modules shared across Devtools).
-
-* [devtools-config](https://github.com/devtools-html/devtools-core/blob/master/packages/devtools-config/#readme) config used in dev server
-* [devtools-launchpad](https://github.com/devtools-html/devtools-core/blob/master/packages/devtools-launchpad/#readme) provide the dev server, landing page and the bootstrap functions to run devtools in the browser tab.
-* [devtools-modules](https://github.com/devtools-html/devtools-core/blob/master/packages/devtools-modules/#readme) Devtools shared and shim modules.
-* [devtools-source-editor](https://github.com/devtools-html/devtools-core/blob/master/packages/devtools-source-editor/#readme) Source Editor component.
-* [devtools-reps](https://github.com/devtools-html/debugger.html/blob/master/packages/devtools-reps/#readme) remote object formatter for variables representation.
-
-Changes to those modules need to be done on Github, using the Pull Request workflow.
-Then, a new version of the modified package need to be released on npm so the version number
-can be updated in WebConsole's `package.json`. Some modules have a release process,
-look for `RELEASE.md` file in the module folder, or ask a maintainer if you are
-unsure about the release process.
-
 ## Code Structure
 
-Top level files are used to launch the WebConsole inside of the DevTools toolbox or run in
-the browser tab (experimental). The same code base is used to run in both environments.
-
-### Run inside of the DevTools toolbox
-
-Files used to run the WebConsole inside of the DevTools toolbox.
+Top level files are used to launch the WebConsole inside of the DevTools toolbox.
+The main files used to run the WebConsole are:
 
 * `main.js` called by devtools toolbox to launch the WebConsole panel.
 * `index.html` panel UI and launch scripts.
 
-### Run in the browser tab (experimental)
-
-Files used to run the WebConsole in the browser tab
-
-* `bin/` files to launch test server.
-* `configs/` dev configs.
-* `local-dev/index.js` the entry point, equivalent to `index.html`.
-* `webpack.config.js` the webpack config file, including plenty of module aliases map to shims and polyfills.
-* `package.json` declare every required packages and available commands.
-
-To run in the browser tab, the WebConsole needs to get some dependencies from npm module.
-Check `package.json` to see all dependencies. Check `webpack.config.js` to find the module alias,
-and check [devtools-core](https://github.com/devtools-html/devtools-core) packages to dive
-into actual modules used by the WebConsole and other Devtools.
-
 ### UI
 
 The WebConsole UI is built using [React](http://docs.firefox-dev.tools/frontend/react.html)
 components (in `components/`).
 
 The React application is rendered from `webconsole-output-wrapper.js`.
-It contains 3 top components:
+It contains 4 top components:
 * **ConsoleOutput** (in `ConsoleOutput.js`) is the component where messages are rendered.
 * **FilterBar** (in `FilterBar.js`) is the component for the filter bars (filter input and toggle buttons).
 * **SideBar** (in `SideBar.js`) is the component that render the sidebar where objects can be placed in.
+* **JsTerm** (in `JsTerm.js`) is the component that render the console input.
 
 We prefer stateless component (defined by function) instead of stateful component
 (defined by class) unless the component has to maintain its internal state.
 
 ### State
 
-Besides the UI, the WebConsole manages the app state via [Redux](When working on console running via launchpad).
+Besides the UI, the WebConsole manages the app state via [Redux].
 The following locations define the app state:
 
 * `src/constants.js` constants used across the tool including action and event names.
@@ -137,8 +51,12 @@ The redux state is a plain javascript object with the following properties:
 {
   // State of the filter input and toggle buttons
   filters,
+  // State of the input history
+  history,
   // Console messages data and state (hidden, expanded, groups, …)
   messages,
+  // State of notifications displayed on the output (e.g. self-XSS warning message)
+  notifications,
   // Preferences (persist message, message limit, …)
   prefs,
   // Interface state (filter bar visible, sidebar visible, …)
diff --git a/devtools/client/webconsole/bin/configure.js b/devtools/client/webconsole/bin/configure.js
deleted file mode 100644
index 38922cee175f..000000000000
--- a/devtools/client/webconsole/bin/configure.js
+++ /dev/null
@@ -1,29 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-/* eslint-env node */
-
-"use strict";
-
-const fs = require("fs");
-const path = require("path");
-
-function getConfig() {
-  if (process.env.TARGET === "firefox-panel") {
-    return require("../configs/firefox-panel.json");
-  }
-
-  const developmentConfig = require("../configs/development.json");
-
-  let localConfig = {};
-  if (fs.existsSync(path.resolve(__dirname, "../configs/local.json"))) {
-    localConfig = require("../configs/local.json");
-  }
-
-  return Object.assign({}, developmentConfig, localConfig);
-}
-
-module.exports = {
-  getConfig,
-};
diff --git a/devtools/client/webconsole/bin/dev-server.js b/devtools/client/webconsole/bin/dev-server.js
deleted file mode 100644
index e1aadfbd5475..000000000000
--- a/devtools/client/webconsole/bin/dev-server.js
+++ /dev/null
@@ -1,19 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-/* eslint-env node */
-
-"use strict";
-
-const toolbox = require("devtools-launchpad/index");
-const feature = require("devtools-config");
-const { getConfig } = require("./configure");
-
-const envConfig = getConfig();
-
-feature.setConfig(envConfig);
-
-const webpackConfig = require("../webpack.config");
-
-toolbox.startDevServer(envConfig, webpackConfig, __dirname);
diff --git a/devtools/client/webconsole/components/JSTerm.js b/devtools/client/webconsole/components/JSTerm.js
index b2b04861803a..bdba98ae5189 100644
--- a/devtools/client/webconsole/components/JSTerm.js
+++ b/devtools/client/webconsole/components/JSTerm.js
@@ -18,7 +18,7 @@ loader.lazyRequireGetter(this, "gDevTools", "devtools/client/framework/devtools"
 loader.lazyRequireGetter(this, "KeyCodes", "devtools/client/shared/keycodes", true);
 loader.lazyRequireGetter(this, "Editor", "devtools/client/sourceeditor/editor");
 loader.lazyRequireGetter(this, "Telemetry", "devtools/client/shared/telemetry");
-loader.lazyRequireGetter(this, "processScreenshot", "devtools/shared/webconsole/screenshot-helper");
+loader.lazyRequireGetter(this, "saveScreenshot", "devtools/shared/screenshot/save");
 
 const l10n = require("devtools/client/webconsole/webconsole-l10n");
 
@@ -473,7 +473,7 @@ class JSTerm extends Component {
           break;
         case "screenshotOutput":
           const { args, value } = helperResult;
-          const results = await processScreenshot(this.hud.window, args, value);
+          const results = await saveScreenshot(this.hud.window, args, value);
           this.screenshotNotify(results);
           // early return as screenshot notify has dispatched all necessary messages
           return null;
@@ -1104,7 +1104,15 @@ class JSTerm extends Component {
         filterBy = input.substring(input.lastIndexOf(lastNonAlpha) + 1);
       }
 
-      const newList = this._autocompleteCache.sort().filter(l => l.startsWith(filterBy));
+      const filterByLc = filterBy.toLocaleLowerCase();
+      const looseMatching = !filterBy || filterBy[0].toLocaleLowerCase() === filterBy[0];
+      const newList = this._autocompleteCache.filter(l => {
+        if (looseMatching) {
+          return l.toLocaleLowerCase().startsWith(filterByLc);
+        }
+
+        return l.startsWith(filterBy);
+      });
 
       this._receiveAutocompleteProperties(null, {
         matches: newList,
@@ -1146,21 +1154,42 @@ class JSTerm extends Component {
       this._autocompleteQuery = inputUntilCursor;
     }
 
-    const matches = message.matches;
-    const lastPart = message.matchProp;
+    const {matches, matchProp} = message;
     if (!matches.length) {
       this.clearCompletion();
       this.emit("autocomplete-updated");
       return;
     }
 
+    const items = matches.map(match => ({
+      preLabel: match.substring(0, matchProp.length),
+      label: match
+    }));
+
+    if (items.length > 0) {
+      const suffix = items[0].label.substring(matchProp.length);
+      this.setAutoCompletionText(suffix);
+    }
+
     const popup = this.autocompletePopup;
-    const items = matches.map(match => ({ preLabel: lastPart, label: match }));
     popup.setItems(items);
 
     const minimumAutoCompleteLength = 2;
 
-    if (items.length >= minimumAutoCompleteLength) {
+    // We want to show the autocomplete popup if:
+    // - there are at least 2 matching results
+    // - OR, if there's 1 result, but whose label does not start like the input (this can
+    //   happen with insensitive search: `num` will match `Number`).
+    // - OR, if there's 1 result, but we can't show the completionText (because there's
+    // some text after the cursor), unless the text in the popup is the same as the input.
+    if (items.length >= minimumAutoCompleteLength
+      || (items.length === 1 && items[0].preLabel !== matchProp)
+      || (
+        items.length === 1
+        && !this.canDisplayAutoCompletionText()
+        && items[0].label !== matchProp
+      )
+    ) {
       let popupAlignElement;
       let xOffset;
       let yOffset;
@@ -1168,12 +1197,12 @@ class JSTerm extends Component {
       if (this.editor) {
         popupAlignElement = this.node.querySelector(".CodeMirror-cursor");
         // We need to show the popup at the ".".
-        xOffset = -1 * lastPart.length * this._inputCharWidth;
+        xOffset = -1 * matchProp.length * this._inputCharWidth;
         yOffset = 5;
       } else if (this.inputNode) {
         const offset = inputUntilCursor.length -
           (inputUntilCursor.lastIndexOf("\n") + 1) -
-          lastPart.length;
+          matchProp.length;
         xOffset = (offset * this._inputCharWidth) + this._chevronWidth;
         popupAlignElement = this.inputNode;
       }
@@ -1185,10 +1214,6 @@ class JSTerm extends Component {
       popup.hidePopup();
     }
 
-    if (items.length > 0) {
-      const suffix = items[0].label.substring(lastPart.length);
-      this.setAutoCompletionText(suffix);
-    }
     this.emit("autocomplete-updated");
   }
 
@@ -1234,22 +1259,21 @@ class JSTerm extends Component {
    */
   acceptProposedCompletion() {
     let completionText = this.getAutoCompletionText();
-    // In some cases the completion text might not be displayed (e.g. there is some text
-    // just after the cursor so we can't display it). In those case, if the popup is
-    // open and has a selectedItem, we use it for completing the input.
-    if (
-      !completionText
-      && this.autocompletePopup.isOpen
-      && this.autocompletePopup.selectedItem
-    ) {
+    let numberOfCharsToReplaceCharsBeforeCursor;
+
+    // If the autocompletion popup is open, we always get the selected element from there,
+    // since the autocompletion text might not be enough (e.g. `dOcUmEn` should
+    // autocomplete to `document`, but the autocompletion text only shows `t`).
+    if (this.autocompletePopup.isOpen && this.autocompletePopup.selectedItem) {
       const {selectedItem} = this.autocompletePopup;
-      completionText = selectedItem.label.substring(selectedItem.preLabel.length);
+      completionText = selectedItem.label;
+      numberOfCharsToReplaceCharsBeforeCursor = selectedItem.preLabel.length;
     }
 
     this.clearCompletion();
 
     if (completionText) {
-      this.insertStringAtCursor(completionText);
+      this.insertStringAtCursor(completionText, numberOfCharsToReplaceCharsBeforeCursor);
     }
   }
 
@@ -1270,16 +1294,21 @@ class JSTerm extends Component {
    * Insert a string into the console at the cursor location,
    * moving the cursor to the end of the string.
    *
-   * @param string str
+   * @param {string} str
+   * @param {int} numberOfCharsToReplaceCharsBeforeCursor - defaults to 0
    */
-  insertStringAtCursor(str) {
+  insertStringAtCursor(str, numberOfCharsToReplaceCharsBeforeCursor = 0) {
     const value = this.getInputValue();
-    const prefix = this.getInputValueBeforeCursor();
+    let prefix = this.getInputValueBeforeCursor();
     const suffix = value.replace(prefix, "");
 
+    if (numberOfCharsToReplaceCharsBeforeCursor) {
+      prefix =
+        prefix.substring(0, prefix.length - numberOfCharsToReplaceCharsBeforeCursor);
+    }
+
     // We need to retrieve the cursor before setting the new value.
     const editorCursor = this.editor && this.editor.getCursor();
-
     this.setInputValue(prefix + str + suffix);
 
     if (this.inputNode) {
@@ -1289,7 +1318,7 @@ class JSTerm extends Component {
       // Set the cursor on the same line it was already at, after the autocompleted text
       this.editor.setCursor({
         line: editorCursor.line,
-        ch: editorCursor.ch + str.length
+        ch: editorCursor.ch + str.length - numberOfCharsToReplaceCharsBeforeCursor
       });
     }
   }
diff --git a/devtools/client/webconsole/components/message-types/NetworkEventMessage.js b/devtools/client/webconsole/components/message-types/NetworkEventMessage.js
index 3e5ec50e032d..55f442552eb2 100644
--- a/devtools/client/webconsole/components/message-types/NetworkEventMessage.js
+++ b/devtools/client/webconsole/components/message-types/NetworkEventMessage.js
@@ -106,7 +106,7 @@ function NetworkEventMessage({
   const xhr = isXHR
     ? dom.span({ className: "xhr" }, l10n.getStr("webConsoleXhrIndicator"))
     : null;
-  const requestUrl = dom.a({ className: "url", title: request.url, onClick: toggle },
+  const requestUrl = dom.span({ className: "url", title: request.url, onClick: toggle },
     request.url);
   const statusBody = statusInfo
     ? dom.a({ className: "status", onClick: toggle }, statusInfo)
diff --git a/devtools/client/webconsole/local-dev/index.js b/devtools/client/webconsole/local-dev/index.js
deleted file mode 100644
index 03ade69fb34a..000000000000
--- a/devtools/client/webconsole/local-dev/index.js
+++ /dev/null
@@ -1,99 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
- /* eslint-env browser */
-
-"use strict";
-
-const React = require("react");
-const ReactDOM = require("react-dom");
-const { EventEmitter } = require("devtools-modules");
-const { Services: { appinfo, pref } } = require("devtools-modules");
-const { bootstrap } = require("devtools-launchpad");
-
-EventEmitter.decorate(window);
-
-require("../../themes/widgets.css");
-require("../../themes/webconsole.css");
-require("../../themes/components-frame.css");
-require("../../themes/light-theme.css");
-require("../../shared/components/reps/reps.css");
-require("../../shared/components/tabs/Tabs.css");
-require("../../shared/components/tabs/TabBar.css");
-require("../../netmonitor/src/assets/styles/httpi.css");
-
-pref("devtools.debugger.remote-timeout", 10000);
-pref("devtools.hud.loglimit", 10000);
-pref("devtools.webconsole.filter.error", true);
-pref("devtools.webconsole.filter.warn", true);
-pref("devtools.webconsole.filter.info", true);
-pref("devtools.webconsole.filter.log", true);
-pref("devtools.webconsole.filter.debug", true);
-pref("devtools.webconsole.filter.css", false);
-pref("devtools.webconsole.filter.net", false);
-pref("devtools.webconsole.filter.netxhr", false);
-pref("devtools.webconsole.ui.filterbar", false);
-pref("devtools.webconsole.inputHistoryCount", 50);
-pref("devtools.webconsole.persistlog", false);
-pref("devtools.webconsole.timestampMessages", false);
-pref("devtools.webconsole.sidebarToggle", true);
-
-const WebConsoleOutputWrapper = require("../webconsole-output-wrapper");
-const WebConsoleFrame = require("../webconsole-frame").WebConsoleFrame;
-
-// Copied from netmonitor/index.js:
-window.addEventListener("DOMContentLoaded", () => {
-  for (const link of document.head.querySelectorAll("link")) {
-    link.href = link.href.replace(/(resource|chrome)\:\/\//, "/");
-  }
-
-  if (appinfo.OS === "Darwin") {
-    document.documentElement.setAttribute("platform", "mac");
-  } else if (appinfo.OS === "Linux") {
-    document.documentElement.setAttribute("platform", "linux");
-  } else {
-    document.documentElement.setAttribute("platform", "win");
-  }
-});
-
-let consoleFrame;
-function onConnect(connection) {
-  // If we are on the main dashboard don't render the component
-  if (!connection || !connection.tabConnection || !connection.tabConnection.tabTarget) {
-    return;
-  }
-
-  // Replicate the DOM that the root component lives within
-  document.querySelector("#mount").innerHTML = `
-    <div id="app-wrapper" class="theme-body">
-      <div id="output-container" role="document" aria-live="polite" />
-    </div>
-  `;
-
-  // Stub out properties that are received from hudservice
-  const owner = {
-    iframeWindow: window,
-    chromeWindow: window,
-    hudId: "hud_0",
-    getDebuggerFrames: () => { },
-    getInspectorSelection: () => { },
-    target: connection.tabConnection.tabTarget,
-    _browserConsole: false,
-    WebConsoleOutputWrapper,
-  };
-  consoleFrame = new WebConsoleFrame(owner);
-  consoleFrame.init().then(function() {
-    console.log("WebConsoleFrame initialized");
-  });
-}
-
-// This is just a hack until the local dev environment includes jsterm
-window.evaluateJS = function(input) {
-  consoleFrame.webConsoleClient.evaluateJSAsync(`${input}`, function(r) {
-    consoleFrame.consoleOutput.dispatchMessageAdd(r);
-  }, {});
-};
-
-document.documentElement.classList.add("theme-light");
-bootstrap(React, ReactDOM).then(onConnect);
diff --git a/devtools/client/webconsole/package.json b/devtools/client/webconsole/package.json
deleted file mode 100644
index 3a335ee696ff..000000000000
--- a/devtools/client/webconsole/package.json
+++ /dev/null
@@ -1,29 +0,0 @@
-{
-  "name": "webconsole",
-  "version": "0.0.1",
-  "engines": {
-    "node": ">=7.10.0"
-  },
-  "scripts": {
-    "start": "cross-env NODE_ENV=production node bin/dev-server",
-    "dev": " cross-env NODE_ENV=development node bin/dev-server"
-  },
-  "dependencies": {
-    "babel-plugin-transform-flow-strip-types": "^6.22.0",
-    "babel-plugin-transform-react-jsx": "^6.24.1",
-    "babel-plugin-transform-object-rest-spread": "^6.26.0",
-    "cross-env": "^3.1.3",
-    "devtools-config": "0.0.12",
-    "devtools-launchpad": "^0.0.119",
-    "devtools-modules": "0.0.37",
-    "file-loader": "^1.1.6",
-    "netmonitor": "file:../netmonitor",
-    "raw-loader": "^0.5.1",
-    "react": "=16.2.0",
-    "react-dom": "=16.2.0",
-    "react-prop-types": "=0.4.0",
-    "react-redux": "=5.0.6",
-    "redux": "^3.7.2",
-    "require-hacker": "^2.1.4"
-  }
-}
diff --git a/devtools/client/webconsole/test/fixtures/DebuggerClient.js b/devtools/client/webconsole/test/fixtures/DebuggerClient.js
deleted file mode 100644
index 650946710a7c..000000000000
--- a/devtools/client/webconsole/test/fixtures/DebuggerClient.js
+++ /dev/null
@@ -1,88 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-"use strict";
-
-// Objects and functions were cherry-picked from devtools/shared/client/main.js, in
-// order to make the console launchpad Worker.
-
-// mock, we only need DebuggerClient.requester
-const DebuggerClient = function(transport) {};
-
-/**
- * A declarative helper for defining methods that send requests to the server.
- *
- * @param packetSkeleton
- *        The form of the packet to send. Can specify fields to be filled from
- *        the parameters by using the |arg| function.
- * @param before
- *        The function to call before sending the packet. Is passed the packet,
- *        and the return value is used as the new packet. The |this| context is
- *        the instance of the client object we are defining a method for.
- * @param after
- *        The function to call after the response is received. It is passed the
- *        response, and the return value is considered the new response that
- *        will be passed to the callback. The |this| context is the instance of
- *        the client object we are defining a method for.
- * @return Request
- *         The `Request` object that is a Promise object and resolves once
- *         we receive the response. (See request method for more details)
- */
-DebuggerClient.requester = function(packetSkeleton, config = {}) {
-  const { before, after } = config;
-  return function(...args) {
-    let outgoingPacket = {
-      to: packetSkeleton.to || this.actor
-    };
-
-    let maxPosition = -1;
-    for (const k of Object.keys(packetSkeleton)) {
-      if (packetSkeleton[k] instanceof DebuggerClient.Argument) {
-        const { position } = packetSkeleton[k];
-        outgoingPacket[k] = packetSkeleton[k].getArgument(args);
-        maxPosition = Math.max(position, maxPosition);
-      } else {
-        outgoingPacket[k] = packetSkeleton[k];
-      }
-    }
-
-    if (before) {
-      outgoingPacket = before.call(this, outgoingPacket);
-    }
-
-    return this.request(outgoingPacket, (response) => {
-      if (after) {
-        const { from } = response;
-        response = after.call(this, response);
-        if (!response.from) {
-          response.from = from;
-        }
-      }
-
-      // The callback is always the last parameter.
-      const thisCallback = args[maxPosition + 1];
-      if (thisCallback) {
-        thisCallback(response);
-      }
-      return response;
-    }, "DebuggerClient.requester request callback");
-  };
-};
-
-function arg(pos) {
-  return new DebuggerClient.Argument(pos);
-}
-
-DebuggerClient.Argument = function(position) {
-  this.position = position;
-};
-
-DebuggerClient.Argument.prototype.getArgument = function(params) {
-  if (!(this.position in params)) {
-    throw new Error("Bad index into params: " + this.position);
-  }
-  return params[this.position];
-};
-
-module.exports = { arg, DebuggerClient };
diff --git a/devtools/client/webconsole/test/mochitest/browser.ini b/devtools/client/webconsole/test/mochitest/browser.ini
index 8dff18db5a24..50dab883c8cc 100644
--- a/devtools/client/webconsole/test/mochitest/browser.ini
+++ b/devtools/client/webconsole/test/mochitest/browser.ini
@@ -200,6 +200,7 @@ skip-if = verify
 [browser_jsterm_autocomplete_return_key.js]
 [browser_jsterm_autocomplete_width.js]
 [browser_jsterm_autocomplete-properties-with-non-alphanumeric-names.js]
+[browser_jsterm_completion_case_sensitivity.js]
 [browser_jsterm_completion.js]
 [browser_jsterm_content_defined_helpers.js]
 [browser_jsterm_copy_command.js]
diff --git a/devtools/client/webconsole/test/mochitest/browser_jsterm_autocomplete_inside_text.js b/devtools/client/webconsole/test/mochitest/browser_jsterm_autocomplete_inside_text.js
index 977d20bac3c5..11ed99e710b0 100644
--- a/devtools/client/webconsole/test/mochitest/browser_jsterm_autocomplete_inside_text.js
+++ b/devtools/client/webconsole/test/mochitest/browser_jsterm_autocomplete_inside_text.js
@@ -49,9 +49,7 @@ async function performTests() {
   EventUtils.synthesizeKey("KEY_ArrowRight");
   await onPopupClose;
   ok(true, "popup was closed");
-  let expectedInput = "dump(window.testB)";
-  is(jsterm.getInputValue(), expectedInput, "input wasn't modified");
-  checkJsTermCursor(jsterm, expectedInput.length, "cursor was moved to the right");
+  checkJsTermValueAndCursor(jsterm, "dump(window.testB)|", "input wasn't modified");
 
   await setInitialState(jsterm);
   EventUtils.synthesizeKey("KEY_ArrowDown");
@@ -69,9 +67,8 @@ async function performTests() {
 
   // At this point the completion suggestion should be accepted.
   ok(!popup.isOpen, "popup is not open");
-  expectedInput = "dump(window.testBugBB)";
-  is(jsterm.getInputValue(), expectedInput, "completion was successful after VK_TAB");
-  checkJsTermCursor(jsterm, expectedInput.length - 1, "cursor location is correct");
+  checkJsTermValueAndCursor(jsterm, "dump(window.testBugBB|)",
+    "completion was successful after VK_TAB");
   ok(!getJsTermCompletionValue(jsterm), "there is no completion text");
 
   info("Test ENTER key when popup is visible with a selected item");
@@ -82,33 +79,40 @@ async function performTests() {
   await onPopupClose;
 
   ok(!popup.isOpen, "popup is not open");
-  expectedInput = "dump(window.testBugAA)";
-  is(jsterm.getInputValue(), expectedInput, "completion was successful after Enter");
-  checkJsTermCursor(jsterm, expectedInput.length - 1, "cursor location is correct");
+  checkJsTermValueAndCursor(jsterm, "dump(window.testBugAA|)",
+    "completion was successful after Enter");
   ok(!getJsTermCompletionValue(jsterm), "there is no completion text");
 
-  info("Test TAB key when there is no autocomplete suggestion");
+  info("Test autocomplete inside parens");
   jsterm.setInputValue("dump()");
   EventUtils.synthesizeKey("KEY_ArrowLeft");
   const onAutocompleteUpdated = jsterm.once("autocomplete-updated");
   EventUtils.sendString("window.testBugA");
   await onAutocompleteUpdated;
+  ok(popup.isOpen, "popup is open");
+  ok(!getJsTermCompletionValue(jsterm), "there is no completion text");
+
+  info("Matching the completion proposal should close the popup");
+  onPopupClose = popup.once("popup-closed");
+  EventUtils.sendString("A");
+  await onPopupClose;
+
+  info("Test TAB key when there is no autocomplete suggestion");
   ok(!popup.isOpen, "popup is not open");
   ok(!getJsTermCompletionValue(jsterm), "there is no completion text");
 
   EventUtils.synthesizeKey("KEY_Tab");
-
-  expectedInput = "dump(window.testBugAA)";
-  is(jsterm.getInputValue(), "dump(window.testBugA\t)", "Tab inserted a tab char");
-  checkJsTermCursor(jsterm, expectedInput.length - 1, "cursor location is correct");
+  checkJsTermValueAndCursor(jsterm, "dump(window.testBugAA\t|)",
+    "completion was successful after Enter");
 }
 
-function setInitialState(jsterm) {
+async function setInitialState(jsterm) {
   jsterm.focus();
   jsterm.setInputValue("dump()");
   EventUtils.synthesizeKey("KEY_ArrowLeft");
 
   const onPopUpOpen = jsterm.autocompletePopup.once("popup-opened");
   EventUtils.sendString("window.testB");
-  return onPopUpOpen;
+  checkJsTermValueAndCursor(jsterm, "dump(window.testB|)");
+  await onPopUpOpen;
 }
diff --git a/devtools/client/webconsole/test/mochitest/browser_jsterm_autocomplete_width.js b/devtools/client/webconsole/test/mochitest/browser_jsterm_autocomplete_width.js
index 2183f2b219a5..6cc0e181329f 100644
--- a/devtools/client/webconsole/test/mochitest/browser_jsterm_autocomplete_width.js
+++ b/devtools/client/webconsole/test/mochitest/browser_jsterm_autocomplete_width.js
@@ -13,11 +13,11 @@ const TEST_URI = `data:text/html;charset=utf-8,
     /* Create prototype-less object so popup does not contain native
      * Object prototype properties.
      */
-    window.x = Object.create(null, Object.getOwnPropertyDescriptors({
+    window.xx = Object.create(null, Object.getOwnPropertyDescriptors({
       ["y".repeat(10)]: 1,
       ["z".repeat(20)]: 2
     }));
-    window.xx = 1;
+    window.xxx = 1;
   </script>
 </head>
 <body>Test</body>`;
@@ -36,14 +36,14 @@ async function performTests() {
 
   const onPopUpOpen = popup.once("popup-opened");
 
-  info(`wait for completion suggestions for "x"`);
-  EventUtils.sendString("x");
+  info(`wait for completion suggestions for "xx"`);
+  EventUtils.sendString("xx");
 
   await onPopUpOpen;
 
   ok(popup.isOpen, "popup is open");
 
-  const expectedPopupItems = ["x", "xx"];
+  const expectedPopupItems = ["xx", "xxx"];
   is(popup.items.map(i => i.label).join("-"), expectedPopupItems.join("-"),
     "popup has expected items");
 
@@ -51,7 +51,7 @@ async function performTests() {
   ok(originalWidth > 2 * jsterm._inputCharWidth,
     "popup is at least wider than the width of the longest list item");
 
-  info(`wait for completion suggestions for "x."`);
+  info(`wait for completion suggestions for "xx."`);
   let onAutocompleteUpdated = jsterm.once("autocomplete-updated");
   EventUtils.sendString(".");
   await onAutocompleteUpdated;
@@ -63,7 +63,7 @@ async function performTests() {
   ok(newPopupWidth > 20 * jsterm._inputCharWidth,
     "popup is at least wider than the width of the longest list item");
 
-  info(`wait for completion suggestions for "x"`);
+  info(`wait for completion suggestions for "xx"`);
   onAutocompleteUpdated = jsterm.once("autocomplete-updated");
   EventUtils.synthesizeKey("KEY_Backspace");
   await onAutocompleteUpdated;
diff --git a/devtools/client/webconsole/test/mochitest/browser_jsterm_completion.js b/devtools/client/webconsole/test/mochitest/browser_jsterm_completion.js
index 01e12ad518af..b7bac4563f54 100644
--- a/devtools/client/webconsole/test/mochitest/browser_jsterm_completion.js
+++ b/devtools/client/webconsole/test/mochitest/browser_jsterm_completion.js
@@ -7,7 +7,10 @@
 
 "use strict";
 
-const TEST_URI = "data:text/html;charset=utf8,<p>test code completion";
+const TEST_URI = `data:text/html;charset=utf8,<p>test code completion
+  <script>
+    foobar = true;
+  </script>`;
 
 add_task(async function() {
   // Run test with legacy JsTerm
@@ -23,18 +26,18 @@ async function performTests() {
   const {autocompletePopup} = jsterm;
 
   // Test typing 'docu'.
-  await setInputValueForAutocompletion(jsterm, "docu");
-  is(jsterm.getInputValue(), "docu", "'docu' completion (input.value)");
-  checkJsTermCompletionValue(jsterm, "    ment", "'docu' completion (completeNode)");
+  await setInputValueForAutocompletion(jsterm, "foob");
+  is(jsterm.getInputValue(), "foob", "'foob' completion (input.value)");
+  checkJsTermCompletionValue(jsterm, "    ar", "'foob' completion (completeNode)");
   is(autocompletePopup.items.length, 1, "autocomplete popup has 1 item");
   is(autocompletePopup.isOpen, false, "autocomplete popup is not open");
 
   // Test typing 'docu' and press tab.
   EventUtils.synthesizeKey("KEY_Tab");
-  is(jsterm.getInputValue(), "document", "'docu' tab completion");
+  is(jsterm.getInputValue(), "foobar", "'foob' tab completion");
 
-  checkJsTermCursor(jsterm, "document".length, "cursor is at the end of 'document'");
-  is(getJsTermCompletionValue(jsterm).replace(/ /g, ""), "", "'docu' completed");
+  checkJsTermCursor(jsterm, "foobar".length, "cursor is at the end of 'foobar'");
+  is(getJsTermCompletionValue(jsterm).replace(/ /g, ""), "", "'foob' completed");
 
   // Test typing 'window.Ob' and press tab.  Just 'window.O' is
   // ambiguous: could be window.Object, window.Option, etc.
diff --git a/devtools/client/webconsole/test/mochitest/browser_jsterm_completion_case_sensitivity.js b/devtools/client/webconsole/test/mochitest/browser_jsterm_completion_case_sensitivity.js
new file mode 100644
index 000000000000..005c585b2b90
--- /dev/null
+++ b/devtools/client/webconsole/test/mochitest/browser_jsterm_completion_case_sensitivity.js
@@ -0,0 +1,101 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set ft=javascript ts=2 et sw=2 tw=80: */
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Tests that code completion works properly in regards to case sensitivity.
+
+"use strict";
+
+const TEST_URI = `data:text/html;charset=utf8,<p>test case-sensitivity completion.
+  <script>
+    fooBar = Object.create(null, Object.getOwnPropertyDescriptors({
+      Foo: 1,
+      test: 2,
+      Test: 3,
+      TEST: 4,
+    }));
+    FooBar = true;
+  </script>`;
+
+add_task(async function() {
+  // Run test with legacy JsTerm
+  await pushPref("devtools.webconsole.jsterm.codeMirror", false);
+  await performTests();
+  // And then run it with the CodeMirror-powered one.
+  await pushPref("devtools.webconsole.jsterm.codeMirror", true);
+  await performTests();
+});
+
+async function performTests() {
+  const {jsterm} = await openNewTabAndConsole(TEST_URI);
+  const {autocompletePopup} = jsterm;
+
+  const checkInput = (expected, assertionInfo) =>
+    checkJsTermValueAndCursor(jsterm, expected, assertionInfo);
+
+  info("Check that lowercased input is case-insensitive");
+  let onPopUpOpen = autocompletePopup.once("popup-opened");
+  EventUtils.sendString("foob");
+  await onPopUpOpen;
+
+  is(getAutocompletePopupLabels(autocompletePopup).join(" - "), "fooBar - FooBar",
+    "popup has expected item, in expected order");
+  checkJsTermCompletionValue(jsterm, "    ar", "completeNode has expected value");
+
+  info("Check that filtering the autocomplete cache is also case insensitive");
+  let onAutoCompleteUpdated = jsterm.once("autocomplete-updated");
+  // Send "a" to make the input "fooba"
+  EventUtils.sendString("a");
+  await onAutoCompleteUpdated;
+
+  checkInput("fooba|");
+  is(getAutocompletePopupLabels(autocompletePopup).join(" - "), "fooBar - FooBar",
+    "popup cache filtering is also case-insensitive");
+  checkJsTermCompletionValue(jsterm, "     r", "completeNode has expected value");
+
+  info("Check that accepting the completion value will change the input casing");
+  let onPopupClose = autocompletePopup.once("popup-closed");
+  EventUtils.synthesizeKey("KEY_Tab");
+  await onPopupClose;
+  checkInput("fooBar|", "The input was completed with the correct casing");
+  checkJsTermCompletionValue(jsterm, "", "completeNode is empty");
+
+  info("Check that the popup is displayed with only 1 matching item");
+  onPopUpOpen = autocompletePopup.once("popup-opened");
+  EventUtils.sendString(".f");
+  await onPopUpOpen;
+
+  // Here we want to match "Foo", and since the completion text will only be "oo", we want
+  // to display the popup so the user knows that we are matching "Foo" and not "foo".
+  checkInput("fooBar.f|");
+  ok(true, "The popup was opened even if there's 1 item matching");
+  is(getAutocompletePopupLabels(autocompletePopup).join(" - "), "Foo",
+    "popup has expected item");
+  checkJsTermCompletionValue(jsterm, "        oo", "completeNode has expected value");
+
+  onPopupClose = autocompletePopup.once("popup-closed");
+  EventUtils.synthesizeKey("KEY_Tab");
+  await onPopupClose;
+  checkInput("fooBar.Foo|", "The input was completed with the correct casing");
+  checkJsTermCompletionValue(jsterm, "", "completeNode is empty");
+
+  jsterm.setInputValue("");
+
+  info("Check that filtering the cache works like on the server");
+  onPopUpOpen = autocompletePopup.once("popup-opened");
+  EventUtils.sendString("fooBar.");
+  await onPopUpOpen;
+  is(getAutocompletePopupLabels(autocompletePopup).join(" - "),
+    "test - Foo - TEST - Test", "popup has expected items");
+
+  onAutoCompleteUpdated = jsterm.once("autocomplete-updated");
+  EventUtils.sendString("T");
+  await onAutoCompleteUpdated;
+  is(getAutocompletePopupLabels(autocompletePopup).join(" - "), "TEST - Test",
+    "popup was filtered case-sensitively, as expected");
+}
+
+function getAutocompletePopupLabels(autocompletePopup) {
+  return autocompletePopup.items.map(i => i.label);
+}
diff --git a/devtools/client/webconsole/test/mochitest/browser_webconsole_object_inspector_scroll.js b/devtools/client/webconsole/test/mochitest/browser_webconsole_object_inspector_scroll.js
index fde7a97f7825..99fb524c2212 100644
--- a/devtools/client/webconsole/test/mochitest/browser_webconsole_object_inspector_scroll.js
+++ b/devtools/client/webconsole/test/mochitest/browser_webconsole_object_inspector_scroll.js
@@ -39,7 +39,8 @@ add_task(async function() {
   });
 
   info("Expand the last node");
-  lastNode.click();
+  const view = lastNode.ownerDocument.defaultView;
+  EventUtils.synthesizeMouseAtCenter(lastNode, {}, view);
   await onOiMutation;
 
   is(scrollTop, outputContainer.scrollTop,
diff --git a/devtools/client/webconsole/webconsole-frame.js b/devtools/client/webconsole/webconsole-frame.js
index 531f4c33de26..482109281ad8 100644
--- a/devtools/client/webconsole/webconsole-frame.js
+++ b/devtools/client/webconsole/webconsole-frame.js
@@ -24,10 +24,6 @@ const PREF_MESSAGE_TIMESTAMP = "devtools.webconsole.timestampMessages";
 const PREF_PERSISTLOG = "devtools.webconsole.persistlog";
 const PREF_SIDEBAR_ENABLED = "devtools.webconsole.sidebarToggle";
 
-// XXX: This file is incomplete (see bug 1326937).
-// It's used when loading the webconsole with devtools-launchpad, but will ultimately be
-// the entry point for the new frontend
-
 /**
  * A WebConsoleFrame instance is an interactive console initialized *per target*
  * that displays console log data as well as provides an interactive terminal to
@@ -236,10 +232,8 @@ WebConsoleFrame.prototype = {
 
     const toolbox = gDevTools.getToolbox(this.owner.target);
 
-    // Handle both launchpad and toolbox loading
-    const Wrapper = this.owner.WebConsoleOutputWrapper || this.window.WebConsoleOutput;
-    this.consoleOutput =
-      new Wrapper(this.outputNode, this, toolbox, this.owner, this.document);
+    this.consoleOutput = new this.window.WebConsoleOutput(
+      this.outputNode, this, toolbox, this.owner, this.document);
     // Toggle the timestamp on preference change
     Services.prefs.addObserver(PREF_MESSAGE_TIMESTAMP, this._onToolboxPrefChanged);
     this._onToolboxPrefChanged();
diff --git a/devtools/client/webconsole/webpack.config.js b/devtools/client/webconsole/webpack.config.js
deleted file mode 100644
index 4b8a8b2aeb72..000000000000
--- a/devtools/client/webconsole/webpack.config.js
+++ /dev/null
@@ -1,160 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-/* eslint-env node */
-/* eslint max-len: [0] */
-
-"use strict";
-
-const {toolboxConfig} = require("./node_modules/devtools-launchpad/index");
-const { NormalModuleReplacementPlugin } = require("webpack");
-const {getConfig} = require("./bin/configure");
-
-const path = require("path");
-const projectPath = path.join(__dirname, "local-dev");
-
-const webpackConfig = {
-  entry: {
-    console: [path.join(projectPath, "index.js")],
-  },
-
-  module: {
-    rules: [
-      {
-        test: /\.(png|svg)$/,
-        loader: "file-loader?name=[path][name].[ext]",
-      },
-      {
-        test: /\.js$/,
-        loaders: [
-          /*
-          * The version of webpack used in the launchpad seems to have trouble
-          * with the require("raw!${file}") that we use for the properties
-          * file in l10.js.
-          * This loader goes through the whole code and remove the "raw!" prefix
-          * so the raw-loader declared in devtools-launchpad config can load
-          * those files.
-          */
-          "rewrite-raw",
-          // Replace all references to this.browserRequire() by require()
-          "rewrite-browser-require",
-          // Replace all references to loader.lazyRequire() by require()
-          "rewrite-lazy-require",
-          // Replace all references to loader.lazyGetter() by require()
-          "rewrite-lazy-getter",
-        ],
-      }
-    ]
-  },
-
-  resolveLoader: {
-    modules: [
-      path.resolve("./node_modules"),
-      path.resolve("../shared/webpack"),
-    ]
-  },
-
-  output: {
-    path: path.join(__dirname, "assets/build"),
-    filename: "[name].js",
-    publicPath: "/assets/build",
-  },
-
-  externals: [
-    {
-      "promise": "var Promise",
-    }
-  ],
-};
-
-webpackConfig.resolve = {
-  modules: [
-    // Make sure webpack is always looking for modules in
-    // `webconsole/node_modules` directory first.
-    path.resolve(__dirname, "node_modules"), "node_modules"
-  ],
-  alias: {
-    "Services": "devtools-modules/src/Services",
-
-    "devtools/client/webconsole/utils": path.join(__dirname, "test/fixtures/WebConsoleUtils"),
-
-    "devtools/client/shared/vendor/immutable": "immutable",
-    "devtools/client/shared/vendor/react": "react",
-    "devtools/client/shared/vendor/react-dom": "react-dom",
-    "devtools/client/shared/vendor/react-redux": "react-redux",
-    "devtools/client/shared/vendor/redux": "redux",
-    "devtools/client/shared/vendor/reselect": "reselect",
-
-    "resource://gre/modules/AppConstants.jsm": path.join(__dirname, "../../client/shared/webpack/shims/app-constants-stub"),
-
-    "devtools/client/framework/devtools": path.join(__dirname, "../../client/shared/webpack/shims/framework-devtools-shim"),
-    "devtools/client/framework/menu": "devtools-modules/src/menu",
-    "devtools/client/sourceeditor/editor": "devtools-source-editor/src/source-editor",
-
-    "devtools/client/shared/unicode-url": "./node_modules/devtools-modules/src/unicode-url",
-    "devtools/client/shared/zoom-keys": "devtools-modules/src/zoom-keys",
-
-    "devtools/shared/fronts/timeline": path.join(__dirname, "../../client/shared/webpack/shims/fronts-timeline-shim"),
-    "devtools/shared/event-emitter": "devtools-modules/src/utils/event-emitter",
-    "devtools/shared/client/debugger-client": path.join(__dirname, "test/fixtures/DebuggerClient"),
-    "devtools/shared/platform/clipboard": path.join(__dirname, "../../client/shared/webpack/shims/platform-clipboard-stub"),
-    "devtools/shared/platform/stack": path.join(__dirname, "../../client/shared/webpack/shims/platform-stack-stub"),
-
-    // Locales need to be explicitly mapped to the en-US subfolder
-    "toolkit/locales": path.join(__dirname, "../../../toolkit/locales/en-US"),
-    "devtools/client/locales": path.join(__dirname, "../../client/locales/en-US"),
-    "devtools/shared/locales": path.join(__dirname, "../../shared/locales/en-US"),
-    "devtools/startup/locales": path.join(__dirname, "../../shared/locales/en-US"),
-
-    // Unless a path explicitly needs to be rewritten or shimmed, all devtools paths can
-    // be mapped to ../../
-    "devtools": path.join(__dirname, "../../"),
-  }
-};
-
-const mappings = [
-  [
-    /utils\/menu/, "devtools-launchpad/src/components/shared/menu"
-  ],
-  [
-    /chrome:\/\/devtools\/skin/,
-    (result) => {
-      result.request = result.request
-        .replace("./chrome://devtools/skin", path.join(__dirname, "../themes"));
-    }
-  ],
-  [
-    /chrome:\/\/devtools\/content/,
-    (result) => {
-      result.request = result.request
-        .replace("./chrome://devtools/content", path.join(__dirname, ".."));
-    }
-  ],
-  [
-    /resource:\/\/devtools/,
-    (result) => {
-      result.request = result.request
-        .replace("./resource://devtools/client", path.join(__dirname, ".."));
-    }
-  ],
-];
-
-webpackConfig.plugins = mappings.map(([regex, res]) =>
-  new NormalModuleReplacementPlugin(regex, res));
-
-const basePath = path.join(__dirname, "../../").replace(/\\/g, "\\\\");
-
-const config = toolboxConfig(webpackConfig, getConfig(), {
-  // Exclude to transpile all scripts in devtools/ but not for this folder nor netmonitor.
-  babelExcludes: new RegExp(`^${basePath}(.(?!(webconsole|netmonitor)))*$`),
-  disablePostCSS: true,
-});
-
-// Remove loaders from devtools-launchpad's webpack.config.js
-// * For svg-inline loader:
-//   Webconsole uses file loader to bundle image assets instead of svg-inline-loader
-config.module.rules = config.module.rules
-  .filter((rule) => !["svg-inline-loader"].includes(rule.loader));
-
-module.exports = config;
diff --git a/devtools/server/actors/moz.build b/devtools/server/actors/moz.build
index 0839a42c722a..bd79292d7e5b 100644
--- a/devtools/server/actors/moz.build
+++ b/devtools/server/actors/moz.build
@@ -57,6 +57,7 @@ DevToolsModules(
     'promises.js',
     'reflow.js',
     'root.js',
+    'screenshot.js',
     'source.js',
     'storage.js',
     'string.js',
diff --git a/devtools/server/actors/screenshot.js b/devtools/server/actors/screenshot.js
new file mode 100644
index 000000000000..57adc5bef128
--- /dev/null
+++ b/devtools/server/actors/screenshot.js
@@ -0,0 +1,20 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+const protocol = require("devtools/shared/protocol");
+const {captureScreenshot} = require("devtools/shared/screenshot/capture");
+const {screenshotSpec} = require("devtools/shared/specs/screenshot");
+
+exports.ScreenshotActor = protocol.ActorClassWithSpec(screenshotSpec, {
+  initialize: function(conn, targetActor) {
+    protocol.Actor.prototype.initialize.call(this, conn);
+    this.document = targetActor.window.document;
+  },
+
+  capture: function(args) {
+    return captureScreenshot(args, this.document);
+  }
+});
diff --git a/devtools/server/actors/webconsole.js b/devtools/server/actors/webconsole.js
index 82a7f70e1f20..0ee3ffe191ae 100644
--- a/devtools/server/actors/webconsole.js
+++ b/devtools/server/actors/webconsole.js
@@ -1175,7 +1175,7 @@ WebConsoleActor.prototype =
         this.dbg.removeDebuggee(this.evalWindow);
       }
 
-      matches = result.matches || [];
+      matches = result.matches || new Set();
       matchProp = result.matchProp;
 
       // We consider '$' as alphanumeric because it is used in the names of some
@@ -1183,18 +1183,26 @@ WebConsoleActor.prototype =
       // be seen as break in the evaled string.
       const lastNonAlphaIsDot = /[.][a-zA-Z0-9$\s]*$/.test(reqText);
       if (!lastNonAlphaIsDot) {
-        matches = matches.concat(this._getWebConsoleCommandsCache().filter(n =>
-          // filter out `screenshot` command as it is inaccessible without
-          // the `:` prefix
-          n !== "screenshot" && n.startsWith(result.matchProp)
-        ));
+        this._getWebConsoleCommandsCache().forEach(n => {
+          // filter out `screenshot` command as it is inaccessible without the `:` prefix
+          if (n !== "screenshot" && n.startsWith(result.matchProp)) {
+            matches.add(n);
+          }
+        });
       }
-    }
 
-    // Make sure we return an array with unique items, since `matches` can hold twice
-    // the same function name if it was defined in the content page and match an helper
-    // function (e.g. $, keys, …).
-    matches = [...new Set(matches)].sort();
+      // Sort the results in order to display lowercased item first (e.g. we want to
+      // display `document` then `Document` as we loosely match the user input if the
+      // first letter they typed was lowercase).
+      matches = Array.from(matches).sort((a, b) => {
+        const lA = a[0].toLocaleLowerCase() === a[0];
+        const lB = b[0].toLocaleLowerCase() === b[0];
+        if (lA === lB) {
+          return a < b ? -1 : 1;
+        }
+        return lA ? -1 : 1;
+      });
+    }
 
     return {
       from: this.actorID,
diff --git a/devtools/server/actors/webconsole/moz.build b/devtools/server/actors/webconsole/moz.build
index c7d156a80ff5..c98340a1071a 100644
--- a/devtools/server/actors/webconsole/moz.build
+++ b/devtools/server/actors/webconsole/moz.build
@@ -13,7 +13,6 @@ DevToolsModules(
     'content-process-forward.js',
     'eval-with-debugger.js',
     'message-manager-mock.js',
-    'screenshot.js',
     'utils.js',
     'worker-listeners.js',
 )
diff --git a/devtools/server/actors/webconsole/utils.js b/devtools/server/actors/webconsole/utils.js
index f7f3433c65b3..595868e4c8d7 100644
--- a/devtools/server/actors/webconsole/utils.js
+++ b/devtools/server/actors/webconsole/utils.js
@@ -7,11 +7,10 @@
 
 const {Ci, Cu} = require("chrome");
 
-loader.lazyRequireGetter(this, "screenshot", "devtools/server/actors/webconsole/screenshot", true);
-
-// Note that this is only used in WebConsoleCommands, see $0 and pprint().
+// Note that this is only used in WebConsoleCommands, see $0, screenshot and pprint().
 if (!isWorker) {
   loader.lazyImporter(this, "VariablesView", "resource://devtools/client/shared/widgets/VariablesView.jsm");
+  loader.lazyRequireGetter(this, "captureScreenshot", "devtools/shared/screenshot/capture", true);
 }
 
 const CONSOLE_WORKER_IDS = exports.CONSOLE_WORKER_IDS = [
@@ -599,10 +598,11 @@ WebConsoleCommands._registerOriginal("copy", function(owner, value) {
  *               The arguments to be passed to the screenshot
  * @return void
  */
-WebConsoleCommands._registerOriginal("screenshot", function(owner, args) {
+WebConsoleCommands._registerOriginal("screenshot", function(owner, args = {}) {
   owner.helperResult = (async () => {
     // creates data for saving the screenshot
-    const value = await screenshot(owner, args);
+    // help is handled on the client side
+    const value = await captureScreenshot(args, owner.window.document);
     return {
       type: "screenshotOutput",
       value,
diff --git a/devtools/server/main.js b/devtools/server/main.js
index 533ae3e1ab93..eaf2c7721029 100644
--- a/devtools/server/main.js
+++ b/devtools/server/main.js
@@ -426,6 +426,11 @@ var DebuggerServer = {
       constructor: "AccessibilityActor",
       type: { target: true }
     });
+    this.registerModule("devtools/server/actors/screenshot", {
+      prefix: "screenshot",
+      constructor: "ScreenshotActor",
+      type: { target: true }
+    });
   },
 
   /**
diff --git a/devtools/shared/fronts/moz.build b/devtools/shared/fronts/moz.build
index 70a53a124458..eebfa5f6bf4a 100644
--- a/devtools/shared/fronts/moz.build
+++ b/devtools/shared/fronts/moz.build
@@ -31,6 +31,7 @@ DevToolsModules(
     'preference.js',
     'promises.js',
     'reflow.js',
+    'screenshot.js',
     'storage.js',
     'string.js',
     'styles.js',
diff --git a/devtools/shared/fronts/screenshot.js b/devtools/shared/fronts/screenshot.js
new file mode 100644
index 000000000000..c56cb9ace161
--- /dev/null
+++ b/devtools/shared/fronts/screenshot.js
@@ -0,0 +1,38 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+const {screenshotSpec} = require("devtools/shared/specs/screenshot");
+const saveScreenshot = require("devtools/shared/screenshot/save");
+const protocol = require("devtools/shared/protocol");
+
+const ScreenshotFront = protocol.FrontClassWithSpec(screenshotSpec, {
+  initialize: function(client, form) {
+    protocol.Front.prototype.initialize.call(this, client);
+    this.actorID = form.screenshotActor;
+    this.manage(this);
+  },
+
+  async captureAndSave(window, args) {
+    const screenshot = await this.capture(args);
+    return saveScreenshot(window, args, screenshot);
+  }
+});
+
+// A cache of created fronts: WeakMap<Client, Front>
+const knownFronts = new WeakMap();
+
+/**
+ * Create a screenshot front only when needed
+ */
+function getScreenshotFront(target) {
+  let front = knownFronts.get(target.client);
+  if (front == null && target.form.screenshotActor != null) {
+    front = new ScreenshotFront(target.client, target.form);
+    knownFronts.set(target.client, front);
+  }
+  return front;
+}
+
+exports.getScreenshotFront = getScreenshotFront;
diff --git a/devtools/shared/moz.build b/devtools/shared/moz.build
index c3c38d52b10a..2e490329aa4c 100644
--- a/devtools/shared/moz.build
+++ b/devtools/shared/moz.build
@@ -25,6 +25,7 @@ DIRS += [
     'platform',
     'pretty-fast',
     'qrcode',
+    'screenshot',
     'security',
     'sourcemap',
     'sprintfjs',
diff --git a/devtools/server/actors/webconsole/screenshot.js b/devtools/shared/screenshot/capture.js
similarity index 90%
rename from devtools/server/actors/webconsole/screenshot.js
rename to devtools/shared/screenshot/capture.js
index 61c5b0d7af34..e3da3dff3740 100644
--- a/devtools/server/actors/webconsole/screenshot.js
+++ b/devtools/shared/screenshot/capture.js
@@ -3,25 +3,19 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 "use strict";
-
 const { Cu } = require("chrome");
-const { getRect } = require("devtools/shared/layout/utils");
 const { LocalizationHelper } = require("devtools/shared/l10n");
 
 const CONTAINER_FLASHING_DURATION = 500;
 const STRINGS_URI = "devtools/shared/locales/screenshot.properties";
 const L10N = new LocalizationHelper(STRINGS_URI);
 
-exports.screenshot = function takeAsyncScreenshot(owner, args = {}) {
-  if (args.help) {
-    // Early return as help will be handled on the client side.
-    return null;
-  }
-  return captureScreenshot(args, owner.window.document);
-};
+loader.lazyRequireGetter(this, "getRect", "devtools/shared/layout/utils", true);
 
 /**
  * This function is called to simulate camera effects
+ * @param object document
+ *        The target document.
  */
 function simulateCameraFlash(document) {
   const window = document.defaultView;
@@ -34,21 +28,26 @@ function simulateCameraFlash(document) {
  * createScreenshotData
  */
 function captureScreenshot(args, document) {
+  if (args.help) {
+    return null;
+  }
   if (args.delay > 0) {
     return new Promise((resolve, reject) => {
       document.defaultView.setTimeout(() => {
-        createScreenshotData(document, args).then(resolve, reject);
+        createScreenshotDataURL(document, args).then(resolve, reject);
       }, args.delay * 1000);
     });
   }
-  return createScreenshotData(document, args);
+  return createScreenshotDataURL(document, args);
 }
 
+exports.captureScreenshot = captureScreenshot;
+
 /**
  * This does the dirty work of creating a base64 string out of an
  * area of the browser window
  */
-function createScreenshotData(document, args) {
+function createScreenshotDataURL(document, args) {
   const window = document.defaultView;
   let left = 0;
   let top = 0;
@@ -111,6 +110,8 @@ function createScreenshotData(document, args) {
   });
 }
 
+exports.createScreenshotDataURL = createScreenshotDataURL;
+
 /**
  * We may have a filename specified in args, or we might have to generate
  * one.
@@ -138,3 +139,4 @@ function getFilename(defaultName) {
     timeString
   ) + ".png";
 }
+
diff --git a/devtools/shared/screenshot/moz.build b/devtools/shared/screenshot/moz.build
new file mode 100644
index 000000000000..f8d16a902e6c
--- /dev/null
+++ b/devtools/shared/screenshot/moz.build
@@ -0,0 +1,10 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DevToolsModules(
+    'capture.js',
+    'save.js',
+)
diff --git a/devtools/shared/webconsole/screenshot-helper.js b/devtools/shared/screenshot/save.js
similarity index 88%
rename from devtools/shared/webconsole/screenshot-helper.js
rename to devtools/shared/screenshot/save.js
index bb32ee38185a..56c588a68095 100644
--- a/devtools/shared/webconsole/screenshot-helper.js
+++ b/devtools/shared/screenshot/save.js
@@ -98,8 +98,8 @@ function getFormattedHelpData() {
 
 /**
  * Main entry point in this file; Takes the original arguments that `:screenshot` was
- * called with and the image value from the server, and uses the client window to save
- * the screenshot to the remote debugging machine's memory or clipboard.
+ * called with and the image value from the server, and uses the client window to add
+ * and audio effect.
  *
  * @param object window
  *        The Debugger Client window.
@@ -113,14 +113,14 @@ function getFormattedHelpData() {
  * @return string[]
  *         Response messages from processing the screenshot
  */
-function processScreenshot(window, args = {}, value) {
+function saveScreenshot(window, args = {}, value) {
   if (args.help) {
     const message = getFormattedHelpData();
-    // Wrap meesage in an array so that the return value is consistant with saveScreenshot
+    // Wrap message in an array so that the return value is consistant with save
     return [message];
   }
-  simulateCameraShutter(window.document);
-  return saveScreenshot(window, args, value);
+  simulateCameraShutter(window);
+  return save(args, value);
 }
 
 /**
@@ -129,8 +129,7 @@ function processScreenshot(window, args = {}, value) {
  * @param object document
  *        The Debugger Client document.
  */
-function simulateCameraShutter(document) {
-  const window = document.defaultView;
+function simulateCameraShutter(window) {
   if (Services.prefs.getBoolPref("devtools.screenshot.audio.enabled")) {
     const audioCamera = new window.Audio("resource://devtools/client/themes/audio/shutter.wav");
     audioCamera.play();
@@ -140,9 +139,6 @@ function simulateCameraShutter(document) {
 /**
  * Save the captured screenshot to one of several destinations.
  *
- * @param object window
- *        The Debugger Client window.
- *
  * @param object args
  *        The original args with which the screenshot was called.
  *
@@ -152,18 +148,18 @@ function simulateCameraShutter(document) {
  * @return string[]
  *         Response messages from processing the screenshot.
  */
-async function saveScreenshot(window, args, image) {
+async function save(args, image) {
   const fileNeeded = args.filename ||
     !args.clipboard || args.file;
   const results = [];
 
   if (args.clipboard) {
-    const result = saveToClipboard(window, image.data);
+    const result = saveToClipboard(image.data);
     results.push(result);
   }
 
   if (fileNeeded) {
-    const result = await saveToFile(window, image);
+    const result = await saveToFile(image);
     results.push(result);
   }
   return results;
@@ -173,16 +169,13 @@ async function saveScreenshot(window, args, image) {
  * Save the image data to the clipboard. This returns a promise, so it can
  * be treated exactly like file processing.
  *
- * @param object window
- *        The Debugger Client window.
- *
  * @param string base64URI
  *        The image data encoded in a base64 URI that was sent from the server.
  *
  * @return string
  *         Response message from processing the screenshot.
  */
-function saveToClipboard(window, base64URI) {
+function saveToClipboard(base64URI) {
   try {
     const imageTools = Cc["@mozilla.org/image/tools;1"]
                        .getService(Ci.imgITools);
@@ -212,16 +205,13 @@ function saveToClipboard(window, base64URI) {
  * Save the screenshot data to disk, returning a promise which is resolved on
  * completion.
  *
- * @param object window
- *        The Debugger Client window.
- *
  * @param object image
  *        The image object that was sent from the server.
  *
  * @return string
  *         Response message from processing the screenshot.
  */
-async function saveToFile(window, image) {
+async function saveToFile(image) {
   let filename = image.filename;
 
   // Check there is a .png extension to filename
@@ -258,4 +248,4 @@ async function saveToFile(window, image) {
   }
 }
 
-module.exports = processScreenshot;
+module.exports = saveScreenshot;
diff --git a/devtools/shared/specs/moz.build b/devtools/shared/specs/moz.build
index 43a2abcdf4c4..2dcd598f8255 100644
--- a/devtools/shared/specs/moz.build
+++ b/devtools/shared/specs/moz.build
@@ -42,6 +42,7 @@ DevToolsModules(
     'promises.js',
     'property-iterator.js',
     'reflow.js',
+    'screenshot.js',
     'script.js',
     'source.js',
     'storage.js',
diff --git a/devtools/shared/specs/screenshot.js b/devtools/shared/specs/screenshot.js
new file mode 100644
index 000000000000..58be5e557042
--- /dev/null
+++ b/devtools/shared/specs/screenshot.js
@@ -0,0 +1,32 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+const {RetVal, Arg, generateActorSpec, types} = require("devtools/shared/protocol");
+
+types.addDictType("screenshot.args", {
+  fullpage: "nullable:boolean",
+  file: "nullable:boolean",
+  clipboard: "nullable:boolean",
+  selector: "nullable:string",
+  dpr: "nullable:string",
+  delay: "nullable:string"
+});
+
+const screenshotSpec = generateActorSpec({
+  typeName: "screenshot",
+
+  methods: {
+    capture: {
+      request: {
+        args: Arg(0, "screenshot.args")
+      },
+      response: {
+        value: RetVal("json")}
+    },
+  },
+});
+
+exports.screenshotSpec = screenshotSpec;
+
diff --git a/devtools/shared/webconsole/js-property-provider.js b/devtools/shared/webconsole/js-property-provider.js
index 144f46ed9d0a..f5348f12241e 100644
--- a/devtools/shared/webconsole/js-property-provider.js
+++ b/devtools/shared/webconsole/js-property-provider.js
@@ -180,7 +180,7 @@ function findCompletionBeginning(str) {
  *          If no completion valued could be computed, null is returned,
  *          otherwise a object with the following form is returned:
  *            {
- *              matches: [ string, string, string ],
+ *              matches: Set<string>
  *              matchProp: Last part of the inputValue that was used to find
  *                         the matches-strings.
  *            }
@@ -407,17 +407,25 @@ function getMatchedProps(obj, match) {
  * Get all properties in the given object (and its parent prototype chain) that
  * match a given prefix.
  *
- * @param mixed obj
+ * @param {Mixed} obj
  *        Object whose properties we want to filter.
- * @param string match
+ * @param {string} match
  *        Filter for properties that match this string.
- * @return object
- *         Object that contains the matchProp and the list of names.
+ * @returns {object} which holds the following properties:
+ *            - {string} matchProp.
+ *            - {Set} matches: List of matched properties.
  */
 function getMatchedPropsImpl(obj, match, {chainIterator, getProperties}) {
   const matches = new Set();
   let numProps = 0;
 
+  const insensitiveMatching = match && match[0].toUpperCase() !== match[0];
+  const propertyMatches = prop => {
+    return insensitiveMatching
+      ? prop.toLocaleLowerCase().startsWith(match.toLocaleLowerCase())
+      : prop.startsWith(match);
+  };
+
   // We need to go up the prototype chain.
   const iter = chainIterator(obj);
   for (obj of iter) {
@@ -437,7 +445,7 @@ function getMatchedPropsImpl(obj, match, {chainIterator, getProperties}) {
 
     for (let i = 0; i < props.length; i++) {
       const prop = props[i];
-      if (prop.indexOf(match) != 0) {
+      if (!propertyMatches(prop)) {
         continue;
       }
       if (prop.indexOf("-") > -1) {
@@ -459,7 +467,7 @@ function getMatchedPropsImpl(obj, match, {chainIterator, getProperties}) {
 
   return {
     matchProp: match,
-    matches: [...matches],
+    matches,
   };
 }
 
diff --git a/devtools/shared/webconsole/moz.build b/devtools/shared/webconsole/moz.build
index 0ba7e8e21e44..a93ccff8b505 100644
--- a/devtools/shared/webconsole/moz.build
+++ b/devtools/shared/webconsole/moz.build
@@ -12,6 +12,5 @@ DevToolsModules(
     'client.js',
     'js-property-provider.js',
     'network-helper.js',
-    'screenshot-helper.js',
     'throttle.js',
 )
diff --git a/devtools/shared/webconsole/test/test_jsterm_autocomplete.html b/devtools/shared/webconsole/test/test_jsterm_autocomplete.html
index a4bf1b9a6e6d..91daae91b675 100644
--- a/devtools/shared/webconsole/test/test_jsterm_autocomplete.html
+++ b/devtools/shared/webconsole/test/test_jsterm_autocomplete.html
@@ -67,6 +67,14 @@
       });
       window.emojiObject = Object.create(null);
       window.emojiObject["😎"] = "😎";
+
+      window.insensitiveTestCase = Object.create(null, Object.getOwnPropertyDescriptors({
+        PROP: "",
+        Prop: "",
+        prop: "",
+        PRÖP: "",
+        pröp: "",
+      }));
     `;
     await state.client.evaluateJSAsync(script);
 
@@ -81,6 +89,7 @@
       doAutocompleteProxyThrowsOwnKeys,
       doAutocompleteDotSurroundedBySpaces,
       doAutocompleteAfterOr,
+      doInsensitiveAutocomplete,
     ];
 
     if (!isWorker) {
@@ -182,7 +191,8 @@
     ok(!response.matchProp, "matchProp");
     let keys = Object.getOwnPropertyNames(Object.prototype).sort();
     is(response.matches.length, keys.length, "matches.length");
-    checkObject(response.matches, keys);
+    // checkObject(response.matches, keys);
+    is(response.matches.join(" - "), keys.join(" - "));
   }
 
   async function doAutocompleteArray(client) {
@@ -242,6 +252,41 @@
     is(matches.length, 1, "autocomplete returns expected results");
     is(matches.join("-"), "foobarObject");
   }
+
+  async function doInsensitiveAutocomplete(client) {
+    info("test autocomplete for 'window.insensitiveTestCase.'");
+    let {matches} = await client.autocomplete("window.insensitiveTestCase.");
+    is(matches.join("-"), "prop-pröp-PROP-PRÖP-Prop",
+      "autocomplete returns the expected items, in the expected order");
+
+    info("test autocomplete for 'window.insensitiveTestCase.p'");
+    matches = (await client.autocomplete("window.insensitiveTestCase.p")).matches;
+    is(matches.join("-"), "prop-pröp-PROP-PRÖP-Prop",
+      "autocomplete is case-insensitive when first letter is lowercased");
+
+    info("test autocomplete for 'window.insensitiveTestCase.pRoP'");
+    matches = (await client.autocomplete("window.insensitiveTestCase.pRoP")).matches;
+    is(matches.join("-"), "prop-PROP-Prop",
+      "autocomplete is case-insensitive when first letter is lowercased");
+
+    info("test autocomplete for 'window.insensitiveTestCase.P'");
+    matches = (await client.autocomplete("window.insensitiveTestCase.P")).matches;
+    is(matches.join("-"), "PROP-PRÖP-Prop",
+      "autocomplete is case-sensitive when first letter is uppercased");
+
+    info("test autocomplete for 'window.insensitiveTestCase.PROP'");
+    matches = (await client.autocomplete("window.insensitiveTestCase.PROP")).matches;
+    is(matches.join("-"), "PROP",
+      "autocomplete is case-sensitive when first letter is uppercased");
+
+    info("test autocomplete for 'window.insensitiveTestCase.prö'");
+    matches = (await client.autocomplete("window.insensitiveTestCase.prö")).matches;
+    is(matches.join("-"), "pröp-PRÖP", "expected result with lowercase diacritic");
+
+    info("test autocomplete for 'window.insensitiveTestCase.PRÖ'");
+    matches = (await client.autocomplete("window.insensitiveTestCase.PRÖ")).matches;
+    is(matches.join("-"), "PRÖP", "expected result with uppercase diacritic");
+  }
 </script>
 </body>
 </html>
diff --git a/devtools/shared/webconsole/test/unit/test_js_property_provider.js b/devtools/shared/webconsole/test/unit/test_js_property_provider.js
index a74896a99779..fed67f08c9a9 100644
--- a/devtools/shared/webconsole/test/unit/test_js_property_provider.js
+++ b/devtools/shared/webconsole/test/unit/test_js_property_provider.js
@@ -187,7 +187,7 @@ function runChecks(dbgObject, dbgEnv, sandbox) {
  */
 function test_has_no_results(results) {
   Assert.notEqual(results, null);
-  Assert.equal(results.matches.length, 0);
+  Assert.equal(results.matches.size, 0);
 }
 /**
  * A helper that ensures (required) results were found.
@@ -198,6 +198,6 @@ function test_has_no_results(results) {
  */
 function test_has_result(results, requiredSuggestion) {
   Assert.notEqual(results, null);
-  Assert.ok(results.matches.length > 0);
-  Assert.ok(results.matches.includes(requiredSuggestion));
+  Assert.ok(results.matches.size > 0);
+  Assert.ok(results.matches.has(requiredSuggestion));
 }
diff --git a/dom/base/IDTracker.cpp b/dom/base/IDTracker.cpp
index 87c5e67706d6..f0f98fdfcbf1 100644
--- a/dom/base/IDTracker.cpp
+++ b/dom/base/IDTracker.cpp
@@ -144,11 +144,8 @@ IDTracker::Reset(nsIContent* aFromContent,
 }
 
 void
-IDTracker::ResetWithID(nsIContent* aFromContent,
-                       nsAtom* aID,
-                       bool aWatch)
+IDTracker::ResetWithID(Element& aFrom, nsAtom* aID, bool aWatch)
 {
-  MOZ_ASSERT(aFromContent);
   MOZ_ASSERT(aID);
 
   if (aWatch) {
@@ -158,7 +155,7 @@ IDTracker::ResetWithID(nsIContent* aFromContent,
 
   mReferencingImage = false;
 
-  DocumentOrShadowRoot* docOrShadow = DocOrShadowFromContent(*aFromContent);
+  DocumentOrShadowRoot* docOrShadow = DocOrShadowFromContent(aFrom);
   HaveNewDocumentOrShadowRoot(docOrShadow, aWatch, nsDependentAtomString(aID));
 }
 
diff --git a/dom/base/IDTracker.h b/dom/base/IDTracker.h
index 18b0fab7964b..e4e728e72bfa 100644
--- a/dom/base/IDTracker.h
+++ b/dom/base/IDTracker.h
@@ -78,7 +78,7 @@ public:
    * changes, so ElementChanged won't fire and get() will always return the same
    * value, the current element for the ID.
    */
-  void ResetWithID(nsIContent* aFrom, nsAtom* aID, bool aWatch = true);
+  void ResetWithID(Element& aFrom, nsAtom* aID, bool aWatch = true);
 
   /**
    * Clears the reference. ElementChanged is not triggered. get() will return
diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index 918d90e4f232..908977c04183 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -10042,6 +10042,7 @@ public:
       parser->BlockParser();
       mParser = do_GetWeakReference(parser);
       mDocument = aDocument;
+      mDocument->BlockOnload();
     }
   }
 
@@ -10080,6 +10081,7 @@ private:
       if (parser == docParser) {
         parser->UnblockParser();
         parser->ContinueInterruptedParsingAsync();
+        mDocument->UnblockOnload(false);
       }
     }
     mParser = nullptr;
diff --git a/dom/bindings/moz.build b/dom/bindings/moz.build
index 6131c66d270b..a4fdcc710d77 100644
--- a/dom/bindings/moz.build
+++ b/dom/bindings/moz.build
@@ -95,9 +95,11 @@ LOCAL_INCLUDES += [
     '/media/webrtc/signaling/src/common/time_profiling',
     '/media/webrtc/signaling/src/peerconnection',
     '/media/webrtc/trunk/',
-    '/third_party/msgpack/include',
 ]
 
+if CONFIG['MOZ_LIBPRIO']:
+    LOCAL_INCLUDES += ['/third_party/msgpack/include']
+
 DEFINES['GOOGLE_PROTOBUF_NO_RTTI'] = True
 DEFINES['GOOGLE_PROTOBUF_NO_STATIC_INITIALIZER'] = True
 
diff --git a/dom/chrome-webidl/moz.build b/dom/chrome-webidl/moz.build
index 071cbb8b88f8..f4c2e1ceedd5 100644
--- a/dom/chrome-webidl/moz.build
+++ b/dom/chrome-webidl/moz.build
@@ -44,7 +44,6 @@ WEBIDL_FILES = [
     'MozStorageStatementParams.webidl',
     'MozStorageStatementRow.webidl',
     'PrecompiledScript.webidl',
-    'PrioEncoder.webidl',
     'PromiseDebugging.webidl',
     'StructuredCloneHolder.webidl',
     'WebExtensionContentScript.webidl',
@@ -58,3 +57,9 @@ if CONFIG['MOZ_PLACES']:
         'PlacesEvent.webidl',
         'PlacesObservers.webidl',
     ]
+
+if CONFIG['MOZ_LIBPRIO']:
+    WEBIDL_FILES += [
+        'PrioEncoder.webidl',
+    ]
+
diff --git a/dom/events/Event.cpp b/dom/events/Event.cpp
index 4ffbaae6af63..663716ac3973 100644
--- a/dom/events/Event.cpp
+++ b/dom/events/Event.cpp
@@ -1003,6 +1003,20 @@ Event::DefaultPrevented(CallerType aCallerType) const
          aCallerType == CallerType::System;
 }
 
+bool
+Event::ReturnValue(CallerType aCallerType) const
+{
+  return !DefaultPrevented(aCallerType);
+}
+
+void
+Event::SetReturnValue(bool aReturnValue, CallerType aCallerType)
+{
+  if (!aReturnValue) {
+    PreventDefaultInternal(aCallerType == CallerType::System);
+  }
+}
+
 double
 Event::TimeStamp()
 {
diff --git a/dom/events/Event.h b/dom/events/Event.h
index f7a85688d06f..7b849c4b8eaa 100755
--- a/dom/events/Event.h
+++ b/dom/events/Event.h
@@ -281,6 +281,10 @@ public:
     return mEvent->mFlags.mMultipleActionsPrevented;
   }
 
+  bool ReturnValue(CallerType aCallerType) const;
+
+  void SetReturnValue(bool aReturnValue, CallerType aCallerType);
+
   bool IsTrusted() const
   {
     return mEvent->IsTrusted();
diff --git a/dom/html/nsHTMLContentSink.cpp b/dom/html/nsHTMLContentSink.cpp
index d0584cc6335f..055ae40ec2b7 100644
--- a/dom/html/nsHTMLContentSink.cpp
+++ b/dom/html/nsHTMLContentSink.cpp
@@ -131,6 +131,7 @@ public:
   virtual void SetDocumentCharset(NotNull<const Encoding*> aEncoding) override;
   virtual nsISupports *GetTarget() override;
   virtual bool IsScriptExecuting() override;
+  virtual void ContinueInterruptedParsingAsync() override;
 
   // nsIHTMLContentSink
   NS_IMETHOD OpenContainer(ElementType aNodeType) override;
@@ -175,6 +176,9 @@ protected:
   void NotifyInsert(nsIContent* aContent,
                     nsIContent* aChildContent);
   void NotifyRootInsertion();
+
+private:
+  void ContinueInterruptedParsingIfEnabled();
 };
 
 class SinkContext
@@ -1047,3 +1051,23 @@ HTMLContentSink::IsScriptExecuting()
 {
   return IsScriptExecutingImpl();
 }
+
+void
+HTMLContentSink::ContinueInterruptedParsingIfEnabled()
+{
+  if (mParser->IsParserEnabled()) {
+    static_cast<nsIParser*>(mParser.get())->ContinueInterruptedParsing();
+  }
+}
+
+void
+HTMLContentSink::ContinueInterruptedParsingAsync()
+{
+  nsCOMPtr<nsIRunnable> ev =
+    NewRunnableMethod("HTMLContentSink::ContinueInterruptedParsingIfEnabled",
+                      this,
+                      &HTMLContentSink::ContinueInterruptedParsingIfEnabled);
+
+  nsCOMPtr<nsIDocument> doc = do_QueryInterface(mHTMLDocument);
+  doc->Dispatch(mozilla::TaskCategory::Other, ev.forget());
+}
diff --git a/dom/moz.build b/dom/moz.build
index 741a04267558..b6d13707cf73 100644
--- a/dom/moz.build
+++ b/dom/moz.build
@@ -63,7 +63,6 @@ DIRS += [
     'notification',
     'offline',
     'power',
-    'prio',
     'push',
     'quota',
     'security',
@@ -105,6 +104,9 @@ DIRS += [
     'simpledb',
 ]
 
+if CONFIG['MOZ_LIBPRIO']:
+    DIRS += ['prio']
+
 if CONFIG['OS_ARCH'] == 'WINNT':
     DIRS += ['plugins/ipc/hangui']
 
diff --git a/dom/smil/nsSMILTimeValueSpec.cpp b/dom/smil/nsSMILTimeValueSpec.cpp
index 12fea9b763e9..19bd77a9f0a3 100644
--- a/dom/smil/nsSMILTimeValueSpec.cpp
+++ b/dom/smil/nsSMILTimeValueSpec.cpp
@@ -57,7 +57,7 @@ nsSMILTimeValueSpec::~nsSMILTimeValueSpec()
 
 nsresult
 nsSMILTimeValueSpec::SetSpec(const nsAString& aStringSpec,
-                             Element* aContextNode)
+                             Element& aContextElement)
 {
   nsSMILTimeValueSpecParams params;
 
@@ -80,23 +80,21 @@ nsSMILTimeValueSpec::SetSpec(const nsAString& aStringSpec,
     mParams.mEventSymbol = nsGkAtoms::repeatEvent;
   }
 
-  ResolveReferences(aContextNode);
+  ResolveReferences(aContextElement);
 
   return NS_OK;
 }
 
 void
-nsSMILTimeValueSpec::ResolveReferences(nsIContent* aContextNode)
+nsSMILTimeValueSpec::ResolveReferences(Element& aContextElement)
 {
-  if (mParams.mType != nsSMILTimeValueSpecParams::SYNCBASE && !IsEventBased())
+  if (mParams.mType != nsSMILTimeValueSpecParams::SYNCBASE && !IsEventBased()) {
     return;
-
-  MOZ_ASSERT(aContextNode,
-             "null context node for resolving timing references against");
+  }
 
   // If we're not bound to the document yet, don't worry, we'll get called again
   // when that happens
-  if (!aContextNode->IsInComposedDoc())
+  if (!aContextElement.IsInComposedDoc())
     return;
 
   // Hold ref to the old element so that it isn't destroyed in between resetting
@@ -105,7 +103,7 @@ nsSMILTimeValueSpec::ResolveReferences(nsIContent* aContextNode)
   RefPtr<Element> oldReferencedElement = mReferencedElement.get();
 
   if (mParams.mDependentElemID) {
-    mReferencedElement.ResetWithID(aContextNode, mParams.mDependentElemID);
+    mReferencedElement.ResetWithID(aContextElement, mParams.mDependentElemID);
   } else if (mParams.mType == nsSMILTimeValueSpecParams::EVENT) {
     Element* target = mOwner->GetTargetElement();
     mReferencedElement.ResetWithElement(target);
diff --git a/dom/smil/nsSMILTimeValueSpec.h b/dom/smil/nsSMILTimeValueSpec.h
index b39ad413acbc..fb14a5e8c5d5 100644
--- a/dom/smil/nsSMILTimeValueSpec.h
+++ b/dom/smil/nsSMILTimeValueSpec.h
@@ -48,9 +48,9 @@ public:
   nsSMILTimeValueSpec(nsSMILTimedElement& aOwner, bool aIsBegin);
   ~nsSMILTimeValueSpec();
 
-  nsresult SetSpec(const nsAString& aStringSpec, Element* aContextNode);
-  void     ResolveReferences(nsIContent* aContextNode);
-  bool     IsEventBased() const;
+  nsresult SetSpec(const nsAString& aStringSpec, Element& aContextElement);
+  void ResolveReferences(Element& aContextElement);
+  bool IsEventBased() const;
 
   void     HandleNewInterval(nsSMILInterval& aInterval,
                              const nsSMILTimeContainer* aSrcContainer);
diff --git a/dom/smil/nsSMILTimedElement.cpp b/dom/smil/nsSMILTimedElement.cpp
index e36d7edc9765..624d65a6fe6e 100644
--- a/dom/smil/nsSMILTimedElement.cpp
+++ b/dom/smil/nsSMILTimedElement.cpp
@@ -853,20 +853,21 @@ namespace
 } // namespace
 
 bool
-nsSMILTimedElement::SetAttr(nsAtom* aAttribute, const nsAString& aValue,
+nsSMILTimedElement::SetAttr(nsAtom* aAttribute,
+                            const nsAString& aValue,
                             nsAttrValue& aResult,
-                            Element* aContextNode,
+                            Element& aContextElement,
                             nsresult* aParseResult)
 {
   bool foundMatch = true;
   nsresult parseResult = NS_OK;
 
   if (aAttribute == nsGkAtoms::begin) {
-    parseResult = SetBeginSpec(aValue, aContextNode, RemoveNonDOM);
+    parseResult = SetBeginSpec(aValue, aContextElement, RemoveNonDOM);
   } else if (aAttribute == nsGkAtoms::dur) {
     parseResult = SetSimpleDuration(aValue);
   } else if (aAttribute == nsGkAtoms::end) {
-    parseResult = SetEndSpec(aValue, aContextNode, RemoveNonDOM);
+    parseResult = SetEndSpec(aValue, aContextElement, RemoveNonDOM);
   } else if (aAttribute == nsGkAtoms::fill) {
     parseResult = SetFillMode(aValue);
   } else if (aAttribute == nsGkAtoms::max) {
@@ -928,10 +929,10 @@ nsSMILTimedElement::UnsetAttr(nsAtom* aAttribute)
 
 nsresult
 nsSMILTimedElement::SetBeginSpec(const nsAString& aBeginSpec,
-                                 Element* aContextNode,
+                                 Element& aContextElement,
                                  RemovalTestFunction aRemove)
 {
-  return SetBeginOrEndSpec(aBeginSpec, aContextNode, true /*isBegin*/,
+  return SetBeginOrEndSpec(aBeginSpec, aContextElement, true /*isBegin*/,
                            aRemove);
 }
 
@@ -944,10 +945,10 @@ nsSMILTimedElement::UnsetBeginSpec(RemovalTestFunction aRemove)
 
 nsresult
 nsSMILTimedElement::SetEndSpec(const nsAString& aEndSpec,
-                               Element* aContextNode,
+                               Element& aContextElement,
                                RemovalTestFunction aRemove)
 {
-  return SetBeginOrEndSpec(aEndSpec, aContextNode, false /*!isBegin*/,
+  return SetBeginOrEndSpec(aEndSpec, aContextElement, false /*!isBegin*/,
                            aRemove);
 }
 
@@ -1205,7 +1206,7 @@ nsSMILTimedElement::IsTimeDependent(const nsSMILTimedElement& aOther) const
 }
 
 void
-nsSMILTimedElement::BindToTree(nsIContent* aContextNode)
+nsSMILTimedElement::BindToTree(Element& aContextElement)
 {
   // Reset previously registered milestone since we may be registering with
   // a different time container now.
@@ -1225,12 +1226,12 @@ nsSMILTimedElement::BindToTree(nsIContent* aContextNode)
     // Resolve references to other parts of the tree
     uint32_t count = mBeginSpecs.Length();
     for (uint32_t i = 0; i < count; ++i) {
-      mBeginSpecs[i]->ResolveReferences(aContextNode);
+      mBeginSpecs[i]->ResolveReferences(aContextElement);
     }
 
     count = mEndSpecs.Length();
     for (uint32_t j = 0; j < count; ++j) {
-      mEndSpecs[j]->ResolveReferences(aContextNode);
+      mEndSpecs[j]->ResolveReferences(aContextElement);
     }
   }
 
@@ -1304,7 +1305,7 @@ nsSMILTimedElement::Unlink()
 
 nsresult
 nsSMILTimedElement::SetBeginOrEndSpec(const nsAString& aSpec,
-                                      Element* aContextNode,
+                                      Element& aContextElement,
                                       bool aIsBegin,
                                       RemovalTestFunction aRemove)
 {
@@ -1323,7 +1324,7 @@ nsSMILTimedElement::SetBeginOrEndSpec(const nsAString& aSpec,
   bool hadFailure = false;
   while (tokenizer.hasMoreTokens()) {
     auto spec = MakeUnique<nsSMILTimeValueSpec>(*this, aIsBegin);
-    nsresult rv = spec->SetSpec(tokenizer.nextToken(), aContextNode);
+    nsresult rv = spec->SetSpec(tokenizer.nextToken(), aContextElement);
     if (NS_SUCCEEDED(rv)) {
       timeSpecsList.AppendElement(std::move(spec));
     } else {
@@ -1481,13 +1482,13 @@ nsSMILTimedElement::RebuildTimingState(RemovalTestFunction aRemove)
   if (mAnimationElement->HasAttr(nsGkAtoms::begin)) {
     nsAutoString attValue;
     mAnimationElement->GetAttr(nsGkAtoms::begin, attValue);
-    SetBeginSpec(attValue, mAnimationElement, aRemove);
+    SetBeginSpec(attValue, *mAnimationElement, aRemove);
   }
 
   if (mAnimationElement->HasAttr(nsGkAtoms::end)) {
     nsAutoString attValue;
     mAnimationElement->GetAttr(nsGkAtoms::end, attValue);
-    SetEndSpec(attValue, mAnimationElement, aRemove);
+    SetEndSpec(attValue, *mAnimationElement, aRemove);
   }
 
   mPrevRegisteredMilestone = sMaxMilestone;
diff --git a/dom/smil/nsSMILTimedElement.h b/dom/smil/nsSMILTimedElement.h
index 7b0dc904a066..47f603a2285e 100644
--- a/dom/smil/nsSMILTimedElement.h
+++ b/dom/smil/nsSMILTimedElement.h
@@ -60,7 +60,7 @@ public:
    * Returns the element targeted by the animation element. Needed for
    * registering event listeners against the appropriate element.
    */
-  mozilla::dom::Element* GetTargetElement();
+  Element* GetTargetElement();
 
   /**
    * Methods for supporting the ElementTimeControl interface.
@@ -265,8 +265,8 @@ public:
    * @param aValue      The attribute value.
    * @param aResult     The nsAttrValue object that may be used for storing the
    *                    parsed result.
-   * @param aContextNode The element to use for context when resolving
-   *                     references to other elements.
+   * @param aContextElement The element to use for context when resolving
+   *                        references to other elements.
    * @param[out] aParseResult The result of parsing the attribute. Will be set
    *                          to NS_OK if parsing is successful.
    *
@@ -274,8 +274,8 @@ public:
    * otherwise.
    */
   bool SetAttr(nsAtom* aAttribute, const nsAString& aValue,
-                 nsAttrValue& aResult, Element* aContextNode,
-                 nsresult* aParseResult = nullptr);
+               nsAttrValue& aResult, Element& aContextElement,
+               nsresult* aParseResult = nullptr);
 
   /**
    * Attempts to unset an attribute on this timed element.
@@ -326,18 +326,17 @@ public:
    * Called when the timed element has been bound to the document so that
    * references from this timed element to other elements can be resolved.
    *
-   * @param aContextNode  The node which provides the necessary context for
-   *                      resolving references. This is typically the element in
-   *                      the host language that owns this timed element. Should
-   *                      not be null.
+   * @param aContextElement The element which provides the necessary context for
+   *                        resolving references. This is typically the element
+   *                        in the host language that owns this timed element.
    */
-  void BindToTree(nsIContent* aContextNode);
+  void BindToTree(Element& aContextElement);
 
   /**
    * Called when the target of the animation has changed so that event
    * registrations can be updated.
    */
-  void HandleTargetElementChange(mozilla::dom::Element* aNewTarget);
+  void HandleTargetElementChange(Element* aNewTarget);
 
   /**
    * Called when the timed element has been removed from a document so that
@@ -377,10 +376,10 @@ protected:
   //
 
   nsresult          SetBeginSpec(const nsAString& aBeginSpec,
-                                 Element* aContextNode,
+                                 Element& aContextElement,
                                  RemovalTestFunction aRemove);
   nsresult          SetEndSpec(const nsAString& aEndSpec,
-                               Element* aContextNode,
+                               Element& aContextElement,
                                RemovalTestFunction aRemove);
   nsresult          SetSimpleDuration(const nsAString& aDurSpec);
   nsresult          SetMin(const nsAString& aMinSpec);
@@ -401,7 +400,7 @@ protected:
   void              UnsetFillMode();
 
   nsresult          SetBeginOrEndSpec(const nsAString& aSpec,
-                                      Element* aContextNode,
+                                      Element& aContextElement,
                                       bool aIsBegin,
                                       RemovalTestFunction aRemove);
   void              ClearSpecs(TimeValueSpecList& aSpecs,
diff --git a/dom/svg/SVGAnimationElement.cpp b/dom/svg/SVGAnimationElement.cpp
index 5e28448c35f5..c90ead06a96f 100644
--- a/dom/svg/SVGAnimationElement.cpp
+++ b/dom/svg/SVGAnimationElement.cpp
@@ -185,7 +185,7 @@ SVGAnimationElement::BindToTree(nsIDocument* aDocument,
       UpdateHrefTarget(hrefStr);
     }
 
-    mTimedElement.BindToTree(aParent);
+    mTimedElement.BindToTree(*this);
   }
 
   AnimationNeedsResample();
@@ -234,7 +234,7 @@ SVGAnimationElement::ParseAttribute(int32_t aNamespaceID,
     // try to parse it.
     if (!foundMatch) {
       foundMatch =
-        mTimedElement.SetAttr(aAttribute, aValue, aResult, this, &rv);
+        mTimedElement.SetAttr(aAttribute, aValue, aResult, *this, &rv);
     }
 
     if (foundMatch) {
diff --git a/dom/svg/crashtests/1486488.html b/dom/svg/crashtests/1486488.html
new file mode 100644
index 000000000000..ba61cb277bd6
--- /dev/null
+++ b/dom/svg/crashtests/1486488.html
@@ -0,0 +1,11 @@
+<script>
+function start() {
+  document.replaceChild(id_0, document.childNodes[0]);
+}
+</script>
+<body onload="start()">
+    <svg>
+        <animate id="id_0" begin="s" />
+        <ellipse id="id_1" />
+    </svg>
+</body>
diff --git a/dom/svg/crashtests/crashtests.list b/dom/svg/crashtests/crashtests.list
index fd2cafcbae90..8f62dd1a9d42 100644
--- a/dom/svg/crashtests/crashtests.list
+++ b/dom/svg/crashtests/crashtests.list
@@ -88,3 +88,4 @@ load 1402798.html
 load 1419250-1.html
 load 1420492.html
 load 1477853.html
+load 1486488.html
diff --git a/dom/webidl/Event.webidl b/dom/webidl/Event.webidl
index f66e084d8bfa..2d02ff7ef468 100644
--- a/dom/webidl/Event.webidl
+++ b/dom/webidl/Event.webidl
@@ -37,6 +37,8 @@ interface Event {
   [Pure]
   readonly attribute boolean cancelable;
   [NeedsCallerType]
+  attribute boolean returnValue;
+  [NeedsCallerType]
   void preventDefault();
   [Pure, NeedsCallerType]
   readonly attribute boolean defaultPrevented;
diff --git a/gfx/vr/VRManager.cpp b/gfx/vr/VRManager.cpp
index 2fa59946af7e..dd0983c88325 100644
--- a/gfx/vr/VRManager.cpp
+++ b/gfx/vr/VRManager.cpp
@@ -177,7 +177,8 @@ VRManager::Shutdown()
   if (mVRService) {
     mVRService->Stop();
   }
-  if (gfxPrefs::VRProcessEnabled()) {
+  if (gfxPrefs::VRProcessEnabled() &&
+      VRGPUChild::IsCreated()) {
     RefPtr<Runnable> task = NS_NewRunnableFunction(
       "VRGPUChild::SendStopVRService",
       [] () -> void {
diff --git a/ipc/glue/ProtocolUtils.cpp b/ipc/glue/ProtocolUtils.cpp
index 07be2c37a478..ad1d2ba3b7bc 100644
--- a/ipc/glue/ProtocolUtils.cpp
+++ b/ipc/glue/ProtocolUtils.cpp
@@ -358,15 +358,15 @@ SentinelReadError(const char* aClassName)
 }
 
 bool
-StateTransition(bool aIsDelete, State* aNext)
+StateTransition(bool aIsDelete, LivenessState* aNext)
 {
   switch (*aNext) {
-    case State::Null:
+    case LivenessState::Null:
       if (aIsDelete) {
-        *aNext = State::Dead;
+        *aNext = LivenessState::Dead;
       }
       break;
-    case State::Dead:
+    case LivenessState::Dead:
       return false;
     default:
       return false;
@@ -377,19 +377,19 @@ StateTransition(bool aIsDelete, State* aNext)
 bool
 ReEntrantDeleteStateTransition(bool aIsDelete,
                                bool aIsDeleteReply,
-                               ReEntrantDeleteState* aNext)
+                               ReEntrantDeleteLivenessState* aNext)
 {
   switch (*aNext) {
-    case ReEntrantDeleteState::Null:
+    case ReEntrantDeleteLivenessState::Null:
       if (aIsDelete) {
-        *aNext = ReEntrantDeleteState::Dying;
+        *aNext = ReEntrantDeleteLivenessState::Dying;
       }
       break;
-    case ReEntrantDeleteState::Dead:
+    case ReEntrantDeleteLivenessState::Dead:
       return false;
-    case ReEntrantDeleteState::Dying:
+    case ReEntrantDeleteLivenessState::Dying:
       if (aIsDeleteReply) {
-        *aNext = ReEntrantDeleteState::Dead;
+        *aNext = ReEntrantDeleteLivenessState::Dead;
       }
       break;
     default:
diff --git a/ipc/glue/ProtocolUtils.h b/ipc/glue/ProtocolUtils.h
index 988a9d77ce74..32e42abc7ed4 100644
--- a/ipc/glue/ProtocolUtils.h
+++ b/ipc/glue/ProtocolUtils.h
@@ -773,7 +773,7 @@ DuplicateHandle(HANDLE aSourceHandle,
  */
 void AnnotateSystemError();
 
-enum class State
+enum class LivenessState
 {
   Dead,
   Null,
@@ -781,9 +781,9 @@ enum class State
 };
 
 bool
-StateTransition(bool aIsDelete, State* aNext);
+StateTransition(bool aIsDelete, LivenessState* aNext);
 
-enum class ReEntrantDeleteState
+enum class ReEntrantDeleteLivenessState
 {
   Dead,
   Null,
@@ -794,7 +794,7 @@ enum class ReEntrantDeleteState
 bool
 ReEntrantDeleteStateTransition(bool aIsDelete,
                                bool aIsDeleteReply,
-                               ReEntrantDeleteState* aNext);
+                               ReEntrantDeleteLivenessState* aNext);
 
 /**
  * An endpoint represents one end of a partially initialized IPDL channel. To
diff --git a/ipc/ipdl/ipdl/lower.py b/ipc/ipdl/ipdl/lower.py
index fc554a456a24..ee7d20b10d98 100644
--- a/ipc/ipdl/ipdl/lower.py
+++ b/ipc/ipdl/ipdl/lower.py
@@ -153,7 +153,7 @@ def _actorManager(actor):
 
 
 def _actorState(actor):
-    return ExprSelect(actor, '->', 'mState')
+    return ExprSelect(actor, '->', 'mLivenessState')
 
 
 def _backstagePass():
@@ -1182,9 +1182,9 @@ def _subtreeUsesShmem(p):
 
 def _stateType(hasReentrantDelete):
     if hasReentrantDelete:
-        return Type('mozilla::ipc::ReEntrantDeleteState')
+        return Type('mozilla::ipc::ReEntrantDeleteLivenessState')
     else:
-        return Type('mozilla::ipc::State')
+        return Type('mozilla::ipc::LivenessState')
 
 
 def _startState(hasReentrantDelete):
@@ -1310,8 +1310,8 @@ class Protocol(ipdl.ast.Protocol):
 
     def stateVar(self, actorThis=None):
         if actorThis is not None:
-            return ExprSelect(actorThis, '->', 'mState')
-        return ExprVar('mState')
+            return ExprSelect(actorThis, '->', 'mLivenessState')
+        return ExprVar('mLivenessState')
 
     def fqStateType(self):
         return _stateType(self.decl.type.hasReentrantDelete)
@@ -3464,7 +3464,7 @@ class _GenerateProtocolActorCode(ipdl.ast.Visitor):
             if ptype.hasReentrantDelete:
                 msgVar = ExprVar(params[0].name)
                 ifdying = StmtIf(ExprBinary(
-                    ExprBinary(ExprVar('mState'), '==', self.protocol.dyingState()),
+                    ExprBinary(ExprVar('mLivenessState'), '==', self.protocol.dyingState()),
                     '&&',
                     ExprBinary(
                         ExprBinary(ExprCall(ExprSelect(msgVar, '.', 'is_reply')),
diff --git a/ipc/ipdl/test/cxx/PTestSyncHang.ipdl b/ipc/ipdl/test/cxx/PTestSyncHang.ipdl
index 2dc51dd640cd..ebb340bf4f37 100644
--- a/ipc/ipdl/test/cxx/PTestSyncHang.ipdl
+++ b/ipc/ipdl/test/cxx/PTestSyncHang.ipdl
@@ -7,7 +7,7 @@ protocol PTestSyncHang {
 
 child:
     // Add this unused message so we don't get compiler errors
-    // complaining that mState is an unused private field.
+    // complaining that mLivenessState is an unused private field.
     async UnusedMessage();
 };
 
diff --git a/layout/base/nsCSSFrameConstructor.cpp b/layout/base/nsCSSFrameConstructor.cpp
index 9961afd76d2f..774f2e1c4874 100644
--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -5943,7 +5943,7 @@ nsCSSFrameConstructor::ConstructFramesFromItem(nsFrameConstructorState& aState,
   // guaranteed that they will be started before onload fires.
   computedStyle->StartBackgroundImageLoads();
 
-  nsFrameState savedStateBits = aState.mAdditionalStateBits;
+  AutoRestore<nsFrameState> savedStateBits(aState.mAdditionalStateBits);
   if (item.mIsGeneratedContent) {
     // Ensure that frames created here are all tagged with
     // NS_FRAME_GENERATED_CONTENT.
@@ -5962,8 +5962,6 @@ nsCSSFrameConstructor::ConstructFramesFromItem(nsFrameConstructorState& aState,
     // our generated content flag so we don't release or unbind it ourselves.
     item.mIsGeneratedContent = false;
   }
-
-  aState.mAdditionalStateBits = savedStateBits;
 }
 
 
diff --git a/layout/painting/nsDisplayList.cpp b/layout/painting/nsDisplayList.cpp
index 3c902a103e25..3795f9af882c 100644
--- a/layout/painting/nsDisplayList.cpp
+++ b/layout/painting/nsDisplayList.cpp
@@ -9421,8 +9421,8 @@ nsDisplayMask::CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBuilder
 {
   bool snap;
   float appUnitsPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
-  nsRect displayBound = GetBounds(aDisplayListBuilder, &snap);
-  LayoutDeviceRect bounds = LayoutDeviceRect::FromAppUnits(displayBound, appUnitsPerDevPixel);
+  nsRect displayBounds = GetBounds(aDisplayListBuilder, &snap);
+  LayoutDeviceRect bounds = LayoutDeviceRect::FromAppUnits(displayBounds, appUnitsPerDevPixel);
 
   Maybe<wr::WrImageMask> mask = aManager->CommandBuilder().BuildWrMaskImage(this, aBuilder, aResources,
                                                                             aSc, aDisplayListBuilder,
@@ -9455,7 +9455,9 @@ nsDisplayMask::CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBuilder
                   /*aTransformForScrollData: */ Nothing(),
                   /*aClipNodeId: */ &clipId);
     sc = layer.ptr();
-    aManager->CommandBuilder().PushOverrideForASR(GetActiveScrolledRoot(), Some(clipId));
+    // The whole stacking context will be clipped by us, so no need to have any
+    // parent for the children context's clip.
+    aManager->CommandBuilder().PushOverrideForASR(GetActiveScrolledRoot(), Nothing());
   }
 
   nsDisplaySVGEffects::CreateWebRenderCommands(aBuilder, aResources, *sc, aManager, aDisplayListBuilder);
@@ -9735,11 +9737,41 @@ nsDisplayFilter::CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBuild
     }
   }
 
+  bool snap;
+  float auPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+  nsRect displayBounds = GetBounds(aDisplayListBuilder, &snap);
+  auto bounds = LayoutDeviceRect::FromAppUnits(displayBounds, auPerDevPixel);
+  // NOTE(emilio): this clip is going to be intersected with the clip that's
+  // currently on the clip stack for this item.
+  //
+  // FIXME(emilio, bug 1486557): clipping to "bounds" isn't really necessary.
+  wr::WrClipId clipId =
+    aBuilder.DefineClip(Nothing(), wr::ToRoundedLayoutRect(bounds));
+
   float opacity = mFrame->StyleEffects()->mOpacity;
-  StackingContextHelper sc(aSc, aBuilder, wrFilters, LayoutDeviceRect(), nullptr,
-                           nullptr, opacity != 1.0f && mHandleOpacity ? &opacity : nullptr);
+  StackingContextHelper sc(
+      aSc,
+      aBuilder,
+      wrFilters,
+      LayoutDeviceRect(),
+      nullptr,
+      nullptr,
+      opacity != 1.0f && mHandleOpacity ? &opacity : nullptr,
+      nullptr,
+      nullptr,
+      gfx::CompositionOp::OP_OVER,
+      true,
+      false,
+      Nothing(),
+      &clipId);
+
+  // The whole stacking context will be clipped by us, so no need to have any
+  // parent for the children context's clip.
+  aManager->CommandBuilder().PushOverrideForASR(GetActiveScrolledRoot(), Nothing());
 
   nsDisplaySVGEffects::CreateWebRenderCommands(aBuilder, aResources, sc, aManager, aDisplayListBuilder);
+
+  aManager->CommandBuilder().PopOverrideForASR(GetActiveScrolledRoot());
   return true;
 }
 
diff --git a/layout/reftests/bidi/dirAuto/reftest.list b/layout/reftests/bidi/dirAuto/reftest.list
index 137d1af839e6..83ada72c41f2 100644
--- a/layout/reftests/bidi/dirAuto/reftest.list
+++ b/layout/reftests/bidi/dirAuto/reftest.list
@@ -1,4 +1,4 @@
-== bdi-auto-dir-default.html bdi-auto-dir-default-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == bdi-auto-dir-default.html bdi-auto-dir-default-ref.html # Bug 1392106
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == dir_auto-set-contained-dir-L.html dir_auto-contained-dir-L-ref.html # Bug 1392106
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == dir_auto-set-contained-dir-R.html dir_auto-contained-dir-R-ref.html # Bug 1392106
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == dir_auto-set-contained-invalid-dir-L.html dir_auto-contained-dir-L-ref.html # Bug 1392106
diff --git a/layout/reftests/bidi/reftest.list b/layout/reftests/bidi/reftest.list
index c877cb45e67e..45eb9d075ba3 100644
--- a/layout/reftests/bidi/reftest.list
+++ b/layout/reftests/bidi/reftest.list
@@ -122,9 +122,9 @@ fuzzy-if(skiaContent,0-1,0-3) == 698291-1.html 698291-1-ref.html
 == 698706-1.html 698706-1-ref.html
 == 704837-1.html 704837-1-ref.html
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == 712600-1.html 712600-1-ref.html # Bug 1392106
-== 712600-2.html 712600-2-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == 712600-2.html 712600-2-ref.html # Bug 1392106
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == 712600-2-dyn.html 712600-2-ref.html # Bug 1392106
-== 712600-3.html 712600-3-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == 712600-3.html 712600-3-ref.html # Bug 1392106
 == 718236-1.html 718236-1-ref.html
 == 718236-2.html 718236-2-ref.html
 == 718236-3.html 718236-3-ref.html
@@ -154,24 +154,24 @@ pref(layout.css.xul-tree-pseudos.content.enabled,true) fuzzy-if(xulRuntime.widge
 == 1157726-1.html 1157726-1-ref.html
 == 1161752.html 1161752-ref.html
 == 1161752-5-embed.html 1161752-5-embed-ref.html
-random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-1a-ltr.html brackets-1a-ltr-ref.html
-random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-1a-rtl.html brackets-1a-rtl-ref.html
-random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-1b-ltr.html brackets-1b-ltr-ref.html
-random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-1b-rtl.html brackets-1b-rtl-ref.html
-random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-1c-ltr.html brackets-1c-ltr-ref.html
-random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-1c-rtl.html brackets-1c-rtl-ref.html
-random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-2a-ltr.html brackets-2a-ltr-ref.html
-fuzzy-if(Android,0-254,0-557) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-2a-rtl.html brackets-2a-rtl-ref.html
-random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-2b-ltr.html brackets-2b-ltr-ref.html
-random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-2b-rtl.html brackets-2b-rtl-ref.html
-random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-2c-ltr.html brackets-2c-ltr-ref.html
-fuzzy-if(Android,0-254,0-231) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-2c-rtl.html brackets-2c-rtl-ref.html
-random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-3a-ltr.html brackets-3a-ltr-ref.html
-random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-3a-rtl.html brackets-3a-rtl-ref.html
-random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-3b-ltr.html brackets-3b-ltr-ref.html
-random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-3b-rtl.html brackets-3b-rtl-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-1a-ltr.html brackets-1a-ltr-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-1a-rtl.html brackets-1a-rtl-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-1b-ltr.html brackets-1b-ltr-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-1b-rtl.html brackets-1b-rtl-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-1c-ltr.html brackets-1c-ltr-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-1c-rtl.html brackets-1c-rtl-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-2a-ltr.html brackets-2a-ltr-ref.html # Bug 1392106
+fuzzy-if(Android,0-254,0-557) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-2a-rtl.html brackets-2a-rtl-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-2b-ltr.html brackets-2b-ltr-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-2b-rtl.html brackets-2b-rtl-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-2c-ltr.html brackets-2c-ltr-ref.html # Bug 1392106
+fuzzy-if(Android,0-254,0-231) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-2c-rtl.html brackets-2c-rtl-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-3a-ltr.html brackets-3a-ltr-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-3a-rtl.html brackets-3a-rtl-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-3b-ltr.html brackets-3b-ltr-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == brackets-3b-rtl.html brackets-3b-rtl-ref.html # Bug 1392106
 == 1217833-1.html 1217833-1-ref.html
 == 1217833-2.html 1217833-2-ref.html
 == 1231175-1.html 1231175-1-ref.html
 == 1366623-1.html 1366623-1-ref.html
-== 1426042-1.html 1426042-1-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == 1426042-1.html 1426042-1-ref.html # Bug 1392106
diff --git a/layout/reftests/bugs/reftest.list b/layout/reftests/bugs/reftest.list
index fe670e6452bb..6cdf61970f5b 100644
--- a/layout/reftests/bugs/reftest.list
+++ b/layout/reftests/bugs/reftest.list
@@ -968,7 +968,7 @@ fails == 413027-3.html 413027-3-ref.html
 == 413286-3.html 413286-3-ref.html
 == 413286-4a.html 413286-4-ref.html
 == 413286-4b.html 413286-4-ref.html
-== 413286-5.html 413286-5-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == 413286-5.html 413286-5-ref.html # Bug 1392106
 == 413286-6.html 413286-6-ref.html
 == 413292-1.html 413292-1-ref.html
 fuzzy-if(Android,0-11,0-17) fuzzy-if(webrender,0-1,0-10) == 413361-1.html 413361-1-ref.html # bug 1128229
diff --git a/layout/reftests/canvas/reftest.list b/layout/reftests/canvas/reftest.list
index 9ca8f07769fe..d441a57cdf12 100644
--- a/layout/reftests/canvas/reftest.list
+++ b/layout/reftests/canvas/reftest.list
@@ -102,8 +102,8 @@ fuzzy-if(skiaContent,0-1,0-43) == 1201272-1.html 1201272-1-ref.html
 == 1303534-1.html 1303534-1-ref.html
 
 == 1304353-text-global-alpha-1.html 1304353-text-global-alpha-1-ref.html
-fuzzy-if(winWidget,0-1,0-578) == 1304353-text-global-alpha-2.html 1304353-text-global-alpha-2-ref.html
-fuzzy-if(winWidget,0-94,0-1575) fuzzy-if(cocoaWidget,0-1,0-24) == 1304353-text-global-composite-op-1.html 1304353-text-global-composite-op-1-ref.html
+fuzzy-if(winWidget,0-1,0-578) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == 1304353-text-global-alpha-2.html 1304353-text-global-alpha-2-ref.html # Bug 1392106
+fuzzy-if(winWidget,0-94,0-1575) fuzzy-if(cocoaWidget,0-1,0-24) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == 1304353-text-global-composite-op-1.html 1304353-text-global-composite-op-1-ref.html # Bug 1392106
 
 == text-indent-1a.html text-indent-1-ref.html
 == text-indent-1b.html text-indent-1-ref.html
diff --git a/layout/reftests/counters/reftest.list b/layout/reftests/counters/reftest.list
index 761d137a65f6..46d1d22d6e5e 100644
--- a/layout/reftests/counters/reftest.list
+++ b/layout/reftests/counters/reftest.list
@@ -9,7 +9,7 @@
 == t1202-counter-07-b-test.html t1202-counter-07-b-reference.html
 == t1202-counter-08-b-test.html t1202-counter-08-b-reference.html
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == t1202-counter-09-b-test.html t1202-counter-09-b-reference.html # Bug 1392106
-== t1202-counter-10-b-test.html t1202-counter-10-b-reference.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == t1202-counter-10-b-test.html t1202-counter-10-b-reference.html # Bug 1392106
 == t1202-counter-11-b-test.html t1202-counter-11-b-reference.html
 == t1202-counter-12-b-test.html t1202-counter-12-b-reference.html
 == t1202-counter-13-b-test.html t1202-counter-13-b-reference.html
@@ -26,7 +26,7 @@ random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == t1202-counter-09-b-test.
 == t1202-counters-07-b-test.html t1202-counters-07-b-reference.html
 == t1202-counters-08-b-test.html t1202-counters-08-b-reference.html
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == t1202-counters-09-b-test.html t1202-counters-09-b-reference.html # Bug 1392106
-== t1202-counters-10-b-test.html t1202-counters-10-b-reference.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == t1202-counters-10-b-test.html t1202-counters-10-b-reference.html # Bug 1392106
 == t1202-counters-11-b-test.html t1202-counters-11-b-reference.html
 == t1202-counters-12-b-test.html t1202-counters-12-b-reference.html
 == t1202-counters-13-b-test.html t1202-counters-13-b-reference.html
diff --git a/layout/reftests/css-submit-invalid/button-submit/reftest.list b/layout/reftests/css-submit-invalid/button-submit/reftest.list
index cfb8df94e45c..d398b047dc3f 100644
--- a/layout/reftests/css-submit-invalid/button-submit/reftest.list
+++ b/layout/reftests/css-submit-invalid/button-submit/reftest.list
@@ -13,4 +13,4 @@
 == change-type-submit-control.html invalid-ref.html
 == change-type-not-submit-control.html valid-ref-4.html
 == self-invalid.html about:blank
-== remove-form.html invalid-ref-3.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == remove-form.html invalid-ref-3.html # bug 1392106
diff --git a/layout/reftests/first-letter/reftest.list b/layout/reftests/first-letter/reftest.list
index 1a36da288bee..82f04ff1ce12 100644
--- a/layout/reftests/first-letter/reftest.list
+++ b/layout/reftests/first-letter/reftest.list
@@ -76,7 +76,7 @@ random-if(gtkWidget) random-if(winWidget&&!d2d) == font-text-styles-floater.html
 == overflow-inline-overflow.html overflow-inline-overflow-ref.html
 
 == 1385656.html 1385656-ref.html
-== 1404167-1.html 1404167-1-ref.html
-== 1404167-2.html 1404167-2-ref.html
-== 1404167-3.html 1404167-3-ref.html
-== 1404167-4.html 1404167-4-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == 1404167-1.html 1404167-1-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == 1404167-2.html 1404167-2-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == 1404167-3.html 1404167-3-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == 1404167-4.html 1404167-4-ref.html # Bug 1392106
diff --git a/layout/reftests/forms/textarea/reftest.list b/layout/reftests/forms/textarea/reftest.list
index fbde15894190..f1f5b15a941e 100644
--- a/layout/reftests/forms/textarea/reftest.list
+++ b/layout/reftests/forms/textarea/reftest.list
@@ -13,5 +13,5 @@ fuzzy-if(skiaContent,0-1,0-1) == rtl.html rtl-dynamic-attr.html
 fuzzy-if(skiaContent,0-1,0-1) == rtl.html rtl-dynamic-style.html
 == rtl.html in-dynamic-rtl-doc.html
 fuzzy-if(skiaContent,0-1,0-3) == setvalue-framereconstruction-1.html setvalue-framereconstruction-ref.html
-fuzzy-if(asyncPan&&!layersGPUAccelerated,0-102,0-4168) == padding-scrollbar-placement.html padding-scrollbar-placement-ref.html
+fuzzy-if(asyncPan&&!layersGPUAccelerated,0-102,0-4168) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == padding-scrollbar-placement.html padding-scrollbar-placement-ref.html # Bug 1392106
 == various-cols.html various-cols-ref.html
diff --git a/layout/reftests/mathml/reftest.list b/layout/reftests/mathml/reftest.list
index 4e55b707b6d3..88a74db83816 100644
--- a/layout/reftests/mathml/reftest.list
+++ b/layout/reftests/mathml/reftest.list
@@ -8,7 +8,7 @@ random-if(gtkWidget) == dir-3.html dir-3-ref.html # bug 1309426
 == dir-7.html dir-7-ref.html
 fails == dir-8.html dir-8-ref.html
 fails == dir-9.html dir-9-ref.html # Bug 787215
-== dir-10.html dir-10-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == dir-10.html dir-10-ref.html # Bug 1392106
 == dir-11.html dir-11-ref.html
 == css-spacing-1.html css-spacing-1-ref.html
 pref(mathml.disabled,true) == disabled-scriptlevel-1.html disabled-scriptlevel-1-ref.html
diff --git a/layout/reftests/pagination/reftest.list b/layout/reftests/pagination/reftest.list
index af8ef9197c42..77ce76d84d29 100644
--- a/layout/reftests/pagination/reftest.list
+++ b/layout/reftests/pagination/reftest.list
@@ -2,17 +2,17 @@
 #   and layout/reftests/w3c-css/submitted/multicol3/
 # Pagination tests
 # asserts(3) == abspos-breaking-000.xhtml abspos-breaking-000.ref.xhtml # bug 1067755, 1135556
-== abspos-breaking-001.xhtml abspos-breaking-000.ref.xhtml
-== abspos-breaking-002.xhtml abspos-breaking-000.ref.xhtml
-== abspos-breaking-003.html abspos-breaking-003-ref.html
-== abspos-breaking-004.html abspos-breaking-004-ref.html
-== abspos-breaking-005.html abspos-breaking-005-ref.html
-== abspos-breaking-006.html abspos-breaking-006-ref.html
-pref(layout.css.box-decoration-break.enabled,true) == abspos-breaking-007.html abspos-breaking-007-ref.html
-pref(layout.css.box-decoration-break.enabled,true) == abspos-breaking-008.html abspos-breaking-008-ref.html
-pref(layout.css.box-decoration-break.enabled,true) == abspos-breaking-009.html abspos-breaking-009-ref.html
-pref(layout.css.box-decoration-break.enabled,true) == abspos-breaking-010.html abspos-breaking-010-ref.html
-== abspos-breaking-011.html abspos-breaking-011-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == abspos-breaking-001.xhtml abspos-breaking-000.ref.xhtml # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == abspos-breaking-002.xhtml abspos-breaking-000.ref.xhtml # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == abspos-breaking-003.html abspos-breaking-003-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == abspos-breaking-004.html abspos-breaking-004-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == abspos-breaking-005.html abspos-breaking-005-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == abspos-breaking-006.html abspos-breaking-006-ref.html # Bug 1392106
+pref(layout.css.box-decoration-break.enabled,true) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == abspos-breaking-007.html abspos-breaking-007-ref.html # Bug 1392106
+pref(layout.css.box-decoration-break.enabled,true) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == abspos-breaking-008.html abspos-breaking-008-ref.html # Bug 1392106
+pref(layout.css.box-decoration-break.enabled,true) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == abspos-breaking-009.html abspos-breaking-009-ref.html # Bug 1392106
+pref(layout.css.box-decoration-break.enabled,true) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == abspos-breaking-010.html abspos-breaking-010-ref.html # Bug 1392106
+== abspos-breaking-011.html abspos-breaking-011-ref.html # Bug 1392106
 == abspos-breaking-dynamic-001.html abspos-breaking-dynamic-001-ref.html
 == abspos-breaking-dynamic-002.html abspos-breaking-dynamic-002-ref.html
 == abspos-breaking-dynamic-003.html abspos-breaking-dynamic-003-ref.html
diff --git a/layout/reftests/svg/filters/css-filters/reftest.list b/layout/reftests/svg/filters/css-filters/reftest.list
index ec8b9668c090..26ecd57d9ffa 100644
--- a/layout/reftests/svg/filters/css-filters/reftest.list
+++ b/layout/reftests/svg/filters/css-filters/reftest.list
@@ -7,12 +7,12 @@ fuzzy-if(webrender,9-9,4780-4784) == blur.html blur-ref.html
 == blur.svg blur-ref.svg
 == blur-calc.html blur-calc-ref.html
 == blur-calc-negative.html blur-calc-negative-ref.html
-skip-if(d2d) == blur-cap-large-radius-on-software.html blur-cap-large-radius-on-software-ref.html
+fuzzy-if(webrender,2-3,55913-56457) skip-if(d2d) == blur-cap-large-radius-on-software.html blur-cap-large-radius-on-software-ref.html
 fuzzy-if(webrender,9-9,4780-4784) == blur-em-radius.html blur-em-radius-ref.html
 == blur-invalid-radius.html blur-invalid-radius-ref.html
 fuzzy-if(webrender,9-9,4780-4784) == blur-rem-radius.html blur-rem-radius-ref.html
 == blur-zero-radius.html blur-zero-radius-ref.html
-fuzzy-if(webrender,6-7,20420-21308) == blur-zoomed-page.html blur-zoomed-page-ref.html
+fuzzy-if(webrender,5-7,19040-21308) == blur-zoomed-page.html blur-zoomed-page-ref.html
 == brightness.html brightness-ref.html
 == brightness-darken.html brightness-darken-ref.html
 == brightness-extreme.html brightness-extreme-ref.html
diff --git a/layout/reftests/svg/reftest.list b/layout/reftests/svg/reftest.list
index 3623d48685f4..a64e50bbd802 100644
--- a/layout/reftests/svg/reftest.list
+++ b/layout/reftests/svg/reftest.list
@@ -478,7 +478,7 @@ fuzzy-if(skiaContent,0-1,0-610) == textPath-03.svg pass.svg
 == textPath-04.svg pass.svg
 == textPath-05.html pass.svg
 == textPath-06.svg pass.svg
-== textPath-line-01.svg textPath-line-01-ref.svg
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == textPath-line-01.svg textPath-line-01-ref.svg # bug 1392106
 == textPath-path-attribute-01.svg textPath-path-attribute-01-ref.svg
 == textPath-side-attribute-01.svg pass.svg
 
@@ -503,7 +503,7 @@ random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) fuzzy-if(skiaContent,0-1,0-
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) fuzzy-if(skiaContent,0-1,0-550) == tspan-rotate-04.svg tspan-rotate-04-ref.svg # bug 1392106
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) fuzzy-if(skiaContent,0-1,0-550) == tspan-rotate-05.svg tspan-rotate-ref.svg # bug 1392106
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) fuzzy-if(skiaContent,0-1,0-550) == tspan-rotate-06.svg tspan-rotate-ref.svg # bug 1392106
-== tspan-rotate-07.svg tspan-rotate-07-ref.svg
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == tspan-rotate-07.svg tspan-rotate-07-ref.svg # Bug 1392106
 == tspan-rotate-textPath-01.svg tspan-rotate-textPath-01-ref.svg
 fuzzy-if(skiaContent,0-1,0-100) == tspan-xy-01.svg tspan-xy-ref.svg
 == tspan-xy-02.svg tspan-xy-ref.svg
diff --git a/layout/reftests/svg/text/reftest.list b/layout/reftests/svg/text/reftest.list
index a270e1a356f4..ef4ef207c89d 100644
--- a/layout/reftests/svg/text/reftest.list
+++ b/layout/reftests/svg/text/reftest.list
@@ -145,14 +145,14 @@ fuzzy-if(/^Windows\x20NT\x2010\.0/.test(http.oscpu)||/^Windows\x20NT\x206\.[12]/
 == ignore-padding.svg ignore-prop-ref.svg
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == ignore-vertical-align.svg ignore-vertical-align-ref.svg # Bug 1392106
 == ignore-overflow-scroll.svg ignore-prop-ref.svg
-== ignore-text-align.svg ignore-prop-ref.svg
-== ignore-text-align-2.svg ignore-text-align-2-ref.svg
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == ignore-text-align.svg ignore-prop-ref.svg # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == ignore-text-align-2.svg ignore-text-align-2-ref.svg # Bug 1392106
 
 # pseudo-elements
 == pseudo-first-line.svg pseudo-first-line-ref.svg
 == pseudo-first-line-2.svg pseudo-first-line-2-ref.svg
-== pseudo-first-letter.svg pseudo-first-letter-ref.svg
-== pseudo-first-letter-2.svg pseudo-first-letter-2-ref.svg
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == pseudo-first-letter.svg pseudo-first-letter-ref.svg # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == pseudo-first-letter-2.svg pseudo-first-letter-2-ref.svg # Bug 1392106
 == ignore-before-after.svg ignore-prop-ref.svg
 
 # invalid child nodes
@@ -179,8 +179,8 @@ fuzzy-if(skiaContent&&winWidget,0-53,0-112) == mask-content-2.svg mask-content-2
 
 # text and clipPaths
 == clipPath-applied.svg clipPath-applied-ref.svg
-fuzzy-if(skiaContent&&winWidget,0-105,0-56) == clipPath-content.svg clipPath-content-ref.svg
-fuzzy-if(skiaContent&&winWidget,0-53,0-112) == clipPath-content-2.svg clipPath-content-2-ref.svg
+fuzzy-if(skiaContent&&winWidget,0-105,0-56) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == clipPath-content.svg clipPath-content-ref.svg # Bug 1392106
+fuzzy-if(skiaContent&&winWidget,0-53,0-112) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == clipPath-content-2.svg clipPath-content-2-ref.svg # Bug 1392106
 
 # text and patterns
 fuzzy-if(cocoaWidget,0-1,0-6) fuzzy-if(skiaContent,0-65,0-313) == pattern-content.svg pattern-content-ref.svg
diff --git a/layout/reftests/text/reftest.list b/layout/reftests/text/reftest.list
index e950d625a64c..7afad03ed82c 100644
--- a/layout/reftests/text/reftest.list
+++ b/layout/reftests/text/reftest.list
@@ -322,7 +322,7 @@ pref(gfx.font_rendering.graphite.enabled,true) == glyph-decomposition-graphite.h
 == hyphenation-control-3.html hyphenation-control-3-ref.html
 == hyphenation-control-4.html hyphenation-control-4-ref.html
 fuzzy-if(winWidget,0-47,0-6) == hyphenation-control-5.html hyphenation-control-5-ref.html
-== hyphenation-control-6.html hyphenation-control-6-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == hyphenation-control-6.html hyphenation-control-6-ref.html # Bug 1392106
 == hyphenation-control-7.html hyphenation-control-7-ref.html
 
 # osx-font-smoothing - with and without subpixel AA, only under OSX
diff --git a/layout/reftests/w3c-css/failures.list b/layout/reftests/w3c-css/failures.list
index cbb747f550c6..31eb2b6d146c 100644
--- a/layout/reftests/w3c-css/failures.list
+++ b/layout/reftests/w3c-css/failures.list
@@ -130,10 +130,13 @@ fuzzy-if(OSX,0-23,0-16) css-writing-modes/text-combine-upright-decorations-001.h
 fuzzy-if(OSX||winWidget,0-255,0-480)  css-writing-modes/text-indent-v??-0??.xht
 fuzzy-if(OSX||winWidget,0-226,0-960) fails-if(webrender&&cocoaWidget)  css-writing-modes/text-orientation-016.xht
 fuzzy-if(OSX||winWidget,0-223,0-720)  css-writing-modes/vertical-alignment-*.xht
-fuzzy-if(OSX||winWidget,0-158,0-624)  css-writing-modes/writing-mode-vertical-??-00?.*
+fuzzy-if(OSX||winWidget,0-158,0-624)  random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) css-writing-modes/writing-mode-vertical-??-00?.*
 fuzzy(0-255,0-960) css-writing-modes/text-combine-upright-value-all-00?.html
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) css-writing-modes/text-combine-upright-compression-00?.html
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) css-writing-modes/text-combine-upright-inherit-all-00?.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) css-writing-modes/text-orientation-0??.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) css-writing-modes/text-orientation-mixed-v??-1??.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) css-writing-modes/text-orientation-sideways-v??-1??.html
 
 # Bug 1167911
 skip css-writing-modes/abs-pos-non-replaced-icb-vlr-021.xht
diff --git a/layout/reftests/w3c-css/received/reftest.list b/layout/reftests/w3c-css/received/reftest.list
index 7977493e1737..9ddedaab7b94 100644
--- a/layout/reftests/w3c-css/received/reftest.list
+++ b/layout/reftests/w3c-css/received/reftest.list
@@ -1121,10 +1121,10 @@ fuzzy-if(OSX||winWidget,0-255,0-480) == css-writing-modes/text-indent-vrl-014.xh
 fuzzy-if(OSX||winWidget,0-255,0-480) == css-writing-modes/text-indent-vrl-016.xht css-writing-modes/text-indent-vrl-012-ref.xht
 fuzzy-if(OSX||winWidget,0-226,0-960) fails-if(webrender&&cocoaWidget) == css-writing-modes/text-orientation-016.xht css-writing-modes/text-orientation-016-ref.xht
 == css-writing-modes/text-orientation-mixed-srl-016.xht css-writing-modes/text-orientation-mixed-srl-016-ref.xht
-== css-writing-modes/text-orientation-mixed-vlr-100.html css-writing-modes/text-orientation-mixed-vlr-100-ref.html
-== css-writing-modes/text-orientation-mixed-vrl-100.html css-writing-modes/text-orientation-mixed-vrl-100-ref.html
-== css-writing-modes/text-orientation-sideways-vlr-100.html css-writing-modes/text-orientation-sideways-vlr-100-ref.html
-== css-writing-modes/text-orientation-sideways-vrl-100.html css-writing-modes/text-orientation-sideways-vrl-100-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == css-writing-modes/text-orientation-mixed-vlr-100.html css-writing-modes/text-orientation-mixed-vlr-100-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == css-writing-modes/text-orientation-mixed-vrl-100.html css-writing-modes/text-orientation-mixed-vrl-100-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == css-writing-modes/text-orientation-sideways-vlr-100.html css-writing-modes/text-orientation-sideways-vlr-100-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == css-writing-modes/text-orientation-sideways-vrl-100.html css-writing-modes/text-orientation-sideways-vrl-100-ref.html
 == css-writing-modes/text-orientation-upright-srl-018.xht css-writing-modes/text-orientation-mixed-srl-016-ref.xht
 == css-writing-modes/text-orientation-upright-vlr-100.html css-writing-modes/text-orientation-upright-vlr-100-ref.html
 == css-writing-modes/text-orientation-upright-vrl-100.html css-writing-modes/text-orientation-upright-vrl-100-ref.html
@@ -1159,10 +1159,10 @@ fails == css-writing-modes/wm-propagation-body-011.xht css-writing-modes/wm-prop
 fails == css-writing-modes/wm-propagation-body-015.xht css-writing-modes/block-flow-direction-025-ref.xht
 == css-writing-modes/writing-mode-horizontal-001l.html css-writing-modes/reference/writing-mode-horizontal-001l-ref.html
 == css-writing-modes/writing-mode-horizontal-001r.html css-writing-modes/reference/writing-mode-horizontal-001r-ref.html
-fuzzy-if(OSX||winWidget,0-158,0-624) == css-writing-modes/writing-mode-vertical-lr-002.xht css-writing-modes/reftest/writing-mode-vertical-lr-002-ref.xht
-fuzzy-if(OSX||winWidget,0-158,0-624) == css-writing-modes/writing-mode-vertical-rl-001.xht css-writing-modes/reftest/writing-mode-vertical-rl-001-ref.xht
-fuzzy-if(OSX||winWidget,0-158,0-624) == css-writing-modes/writing-mode-vertical-rl-002.xht css-writing-modes/reftest/writing-mode-vertical-rl-002-ref.xht
-fuzzy-if(OSX||winWidget,0-158,0-624) == css-writing-modes/writing-mode-vertical-rl-003.htm css-writing-modes/writing-mode-vertical-rl-003-ref.htm
+fuzzy-if(OSX||winWidget,0-158,0-624) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == css-writing-modes/writing-mode-vertical-lr-002.xht css-writing-modes/reftest/writing-mode-vertical-lr-002-ref.xht
+fuzzy-if(OSX||winWidget,0-158,0-624) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == css-writing-modes/writing-mode-vertical-rl-001.xht css-writing-modes/reftest/writing-mode-vertical-rl-001-ref.xht
+fuzzy-if(OSX||winWidget,0-158,0-624) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == css-writing-modes/writing-mode-vertical-rl-002.xht css-writing-modes/reftest/writing-mode-vertical-rl-002-ref.xht
+fuzzy-if(OSX||winWidget,0-158,0-624) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == css-writing-modes/writing-mode-vertical-rl-003.htm css-writing-modes/writing-mode-vertical-rl-003-ref.htm
 skip == selectors/any-link-dynamic-001.html selectors/any-link-dynamic-001-ref.html
 needs-focus == selectors/focus-within-001.html selectors/focus-within-001-ref.html
 needs-focus == selectors/focus-within-002.html selectors/focus-within-001-ref.html
diff --git a/layout/reftests/w3c-css/submitted/counter-styles-3/reftest.list b/layout/reftests/w3c-css/submitted/counter-styles-3/reftest.list
index 30cc3a9b98a0..e339babc6c09 100644
--- a/layout/reftests/w3c-css/submitted/counter-styles-3/reftest.list
+++ b/layout/reftests/w3c-css/submitted/counter-styles-3/reftest.list
@@ -1,6 +1,6 @@
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == system-cyclic.html     system-cyclic-ref.html # Bug 1392106
-== system-fixed.html      system-fixed-ref.html
-== system-symbolic.html   system-symbolic-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == system-fixed.html      system-fixed-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == system-symbolic.html   system-symbolic-ref.html # Bug 1392106
 fails-if(webrender&&cocoaWidget) == system-alphabetic.html system-alphabetic-ref.html
 == system-numeric.html    system-numeric-ref.html
 == system-additive.html   system-additive-ref.html
@@ -13,8 +13,8 @@ fails-if(webrender&&cocoaWidget) == system-alphabetic.html system-alphabetic-ref
 == system-additive-invalid.html   system-common-invalid-ref.html
 == system-extends-invalid.html    system-extends-invalid-ref.html
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == descriptor-negative.html descriptor-negative-ref.html # Bug 1392106
-== descriptor-prefix.html   descriptor-prefix-ref.html
-== descriptor-suffix.html   descriptor-suffix-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == descriptor-prefix.html   descriptor-prefix-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == descriptor-suffix.html   descriptor-suffix-ref.html # Bug 1392106
 == descriptor-range.html    descriptor-range-ref.html
 fuzzy-if(webrender,0-22,0-3) == descriptor-pad.html      descriptor-pad-ref.html
 == descriptor-fallback.html descriptor-fallback-ref.html
diff --git a/layout/reftests/w3c-css/submitted/flexbox/reftest.list b/layout/reftests/w3c-css/submitted/flexbox/reftest.list
index 41abbe8e4c77..198a5ce0ecbb 100644
--- a/layout/reftests/w3c-css/submitted/flexbox/reftest.list
+++ b/layout/reftests/w3c-css/submitted/flexbox/reftest.list
@@ -39,10 +39,10 @@ fuzzy-if(webrender,0-1,0-2) == flexbox-align-self-horiz-004.xhtml  flexbox-align
 == flexbox-align-self-vert-003.xhtml  flexbox-align-self-vert-003-ref.xhtml
 == flexbox-align-self-vert-004.xhtml  flexbox-align-self-vert-004-ref.xhtml
 fuzzy-if(Android,0-158,0-32) == flexbox-align-self-vert-rtl-001.xhtml  flexbox-align-self-vert-rtl-001-ref.xhtml
-== flexbox-align-self-vert-rtl-002.xhtml  flexbox-align-self-vert-rtl-002-ref.xhtml
-== flexbox-align-self-vert-rtl-003.xhtml  flexbox-align-self-vert-rtl-003-ref.xhtml
-== flexbox-align-self-vert-rtl-004.xhtml  flexbox-align-self-vert-rtl-004-ref.xhtml
-== flexbox-align-self-vert-rtl-005.xhtml  flexbox-align-self-vert-rtl-005-ref.xhtml
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == flexbox-align-self-vert-rtl-002.xhtml  flexbox-align-self-vert-rtl-002-ref.xhtml # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == flexbox-align-self-vert-rtl-003.xhtml  flexbox-align-self-vert-rtl-003-ref.xhtml # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == flexbox-align-self-vert-rtl-004.xhtml  flexbox-align-self-vert-rtl-004-ref.xhtml # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == flexbox-align-self-vert-rtl-005.xhtml  flexbox-align-self-vert-rtl-005-ref.xhtml # Bug 1392106
 
 == flexbox-align-items-center-nested-001.html flexbox-align-items-center-nested-001-ref.html
 
diff --git a/layout/reftests/w3c-css/submitted/lists-3/reftest.list b/layout/reftests/w3c-css/submitted/lists-3/reftest.list
index f914145ab8f0..de525942f8e3 100644
--- a/layout/reftests/w3c-css/submitted/lists-3/reftest.list
+++ b/layout/reftests/w3c-css/submitted/lists-3/reftest.list
@@ -1,3 +1,3 @@
 # Tests for list-style-type
-== list-style-type-string-001a.html list-style-type-string-001-ref.html
-== list-style-type-string-001b.html list-style-type-string-001-ref.html
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == list-style-type-string-001a.html list-style-type-string-001-ref.html # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == list-style-type-string-001b.html list-style-type-string-001-ref.html # Bug 1392106
diff --git a/layout/tools/layout-debug/src/nsLayoutDebugCLH.cpp b/layout/tools/layout-debug/src/nsLayoutDebugCLH.cpp
index 2a6db7be58ee..26245cdfa6f4 100644
--- a/layout/tools/layout-debug/src/nsLayoutDebugCLH.cpp
+++ b/layout/tools/layout-debug/src/nsLayoutDebugCLH.cpp
@@ -51,13 +51,17 @@ nsLayoutDebugCLH::Handle(nsICommandLine* aCmdLine)
 
     nsCOMPtr<nsIMutableArray> argsArray = nsArray::Create();
 
-    if (!url.IsEmpty())
-    {
+    if (!url.IsEmpty()) {
+        nsCOMPtr<nsIURI> uri;
+        rv = aCmdLine->ResolveURI(url, getter_AddRefs(uri));
+        NS_ENSURE_SUCCESS(rv, rv);
         nsCOMPtr<nsISupportsString> scriptableURL =
             do_CreateInstance(NS_SUPPORTS_STRING_CONTRACTID);
         NS_ENSURE_TRUE(scriptableURL, NS_ERROR_FAILURE);
-
-        scriptableURL->SetData(url);
+        nsAutoCString resolvedSpec;
+        rv = uri->GetSpec(resolvedSpec);
+        NS_ENSURE_SUCCESS(rv, rv);
+        scriptableURL->SetData(NS_ConvertUTF8toUTF16(resolvedSpec));
         argsArray->AppendElement(scriptableURL);
     }
 
diff --git a/media/webrtc/signaling/src/sdp/sipcc/sdp_utils.c b/media/webrtc/signaling/src/sdp/sipcc/sdp_utils.c
index 4d46115574dc..bcdae9d92263 100644
--- a/media/webrtc/signaling/src/sdp/sipcc/sdp_utils.c
+++ b/media/webrtc/signaling/src/sdp/sipcc/sdp_utils.c
@@ -15,6 +15,13 @@
 
 static const char* logTag = "sdp_utils";
 
+// Actually checks for ASCII only unlike isdigit() on Windows.
+// Also avoids UB issues with isdigit() sign extension when
+// char is signed.
+int sdp_is_ascii_digit(const char c) {
+  return '0' <= c && c <= '9';
+}
+
 sdp_mca_t *sdp_alloc_mca (uint32_t line) {
     sdp_mca_t           *mca_p;
 
@@ -155,7 +162,7 @@ verify_sdescriptions_mki (char *buf, char *mkiVal, uint16_t *mkiLen)
 
     ptr = buf;
     /* MKI must begin with a digit */
-    if (!ptr || (!isdigit((int) *ptr))) {
+    if (!ptr || (!sdp_is_ascii_digit(*ptr))) {
         return FALSE;
     }
 
@@ -166,7 +173,7 @@ verify_sdescriptions_mki (char *buf, char *mkiVal, uint16_t *mkiLen)
             mkiValBuf[idx] = 0;
             ptr++;
             break;
-        } else if ((isdigit((int) *ptr) && (idx < SDP_SRTP_MAX_MKI_SIZE_BYTES-1))) {
+        } else if ((sdp_is_ascii_digit(*ptr) && (idx < SDP_SRTP_MAX_MKI_SIZE_BYTES-1))) {
              mkiValBuf[idx++] = *ptr;
         } else {
              return FALSE;
@@ -184,7 +191,7 @@ verify_sdescriptions_mki (char *buf, char *mkiVal, uint16_t *mkiLen)
 
     /* verify the mki length (max 3 digits) */
     while (*ptr) {
-        if (isdigit((int) *ptr) && (idx < 3)) {
+        if (sdp_is_ascii_digit(*ptr) && (idx < 3)) {
             mkiLenBuf[idx++] = *ptr;
         } else {
             return FALSE;
@@ -251,7 +258,7 @@ verify_sdescriptions_lifetime (char *buf)
                     return FALSE;
                 }
             }
-        } else if (!isdigit((int) *ptr)) {
+        } else if (!sdp_is_ascii_digit(*ptr)) {
                    return FALSE;
         }
 
@@ -282,13 +289,13 @@ sdp_validate_maxprate(const char *string_parm)
     tinybool retval = FALSE;
 
     if (string_parm && (*string_parm)) {
-        while (isdigit((int)*string_parm)) {
+        while (sdp_is_ascii_digit(*string_parm)) {
             string_parm++;
         }
 
         if (*string_parm == '.') {
             string_parm++;
-            while (isdigit((int)*string_parm)) {
+            while (sdp_is_ascii_digit(*string_parm)) {
                 string_parm++;
             }
         }
diff --git a/mobile/android/geckoview/src/main/java/org/mozilla/gecko/gfx/GeckoSurfaceTexture.java b/mobile/android/geckoview/src/main/java/org/mozilla/gecko/gfx/GeckoSurfaceTexture.java
index f5c6dffbdde7..edc50cc0ee2d 100644
--- a/mobile/android/geckoview/src/main/java/org/mozilla/gecko/gfx/GeckoSurfaceTexture.java
+++ b/mobile/android/geckoview/src/main/java/org/mozilla/gecko/gfx/GeckoSurfaceTexture.java
@@ -118,6 +118,18 @@ import org.mozilla.gecko.annotation.WrapForJNI;
         }
     }
 
+    @Override
+    public synchronized void release() {
+        try {
+            super.release();
+            synchronized (sSurfaceTextures) {
+                sSurfaceTextures.remove(mHandle);
+            }
+        } catch (Exception e) {
+            Log.w(LOGTAG, "release() failed", e);
+        }
+    }
+
     @Override
     @WrapForJNI
     public synchronized void releaseTexImage() {
@@ -185,10 +197,6 @@ import org.mozilla.gecko.annotation.WrapForJNI;
 
         for (GeckoSurfaceTexture tex : list) {
             try {
-                synchronized (sSurfaceTextures) {
-                    sSurfaceTextures.remove(tex.mHandle);
-                }
-
                 if (tex.isSingleBuffer()) {
                    tex.releaseTexImage();
                 }
diff --git a/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoSession.java b/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoSession.java
index 1a1e33a01422..e619912245c3 100644
--- a/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoSession.java
+++ b/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoSession.java
@@ -2069,27 +2069,27 @@ public class GeckoSession extends LayerSession
     /**
      * WebResponseInfo contains information about a single web response.
      */
-    public class WebResponseInfo {
+    static public class WebResponseInfo {
         /**
          * The URI of the response. Cannot be null.
          */
-        public final String uri;
+        @NonNull public final String uri;
 
         /**
          * The content type (mime type) of the response. May be null.
          */
-        public final String contentType;
+        @Nullable public final String contentType;
 
         /**
          * The content length of the response. May be 0 if unknokwn.
          */
-        public final long contentLength;
+        @Nullable public final long contentLength;
 
         /**
          * The filename obtained from the content disposition, if any.
          * May be null.
          */
-        public final String filename;
+        @Nullable public final String filename;
 
         /* package */ WebResponseInfo(GeckoBundle message) {
             uri = message.getString("uri");
diff --git a/modules/libpref/init/StaticPrefList.h b/modules/libpref/init/StaticPrefList.h
index f7e7d39686d3..feb614b14b0c 100644
--- a/modules/libpref/init/StaticPrefList.h
+++ b/modules/libpref/init/StaticPrefList.h
@@ -461,6 +461,13 @@ VARCACHE_PREF(
   bool, false
 )
 
+// Is support for CSS column-span enabled?
+VARCACHE_PREF(
+  "layout.css.column-span.enabled",
+   layout_css_column_span_enabled,
+  bool, false
+)
+
 //---------------------------------------------------------------------------
 // JavaScript prefs
 //---------------------------------------------------------------------------
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index cb3154df3749..7fc2a5ea9d59 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -3065,9 +3065,6 @@ pref("layout.css.shape-outside.enabled", true);
 // Is support for document.fonts enabled?
 pref("layout.css.font-loading-api.enabled", true);
 
-// Is support for column-span enabled?
-pref("layout.css.column-span.enabled", false);
-
 // Are inter-character ruby annotations enabled?
 pref("layout.css.ruby.intercharacter.enabled", false);
 
diff --git a/netwerk/protocol/http/Http2Session.cpp b/netwerk/protocol/http/Http2Session.cpp
index 0701ee312cd0..7106fea096d0 100644
--- a/netwerk/protocol/http/Http2Session.cpp
+++ b/netwerk/protocol/http/Http2Session.cpp
@@ -4137,16 +4137,18 @@ Http2Session::BufferOutput(const char *buf,
 bool // static
 Http2Session::ALPNCallback(nsISupports *securityInfo)
 {
-  if (!gHttpHandler->IsH2MandatorySuiteEnabled()) {
-    LOG3(("Http2Session::ALPNCallback Mandatory Cipher Suite Unavailable\n"));
-    return false;
-  }
-
   nsCOMPtr<nsISSLSocketControl> ssl = do_QueryInterface(securityInfo);
   LOG3(("Http2Session::ALPNCallback sslsocketcontrol=%p\n", ssl.get()));
   if (ssl) {
     int16_t version = ssl->GetSSLVersionOffered();
     LOG3(("Http2Session::ALPNCallback version=%x\n", version));
+
+    if (version == nsISSLSocketControl::TLS_VERSION_1_2 &&
+        !gHttpHandler->IsH2MandatorySuiteEnabled()) {
+      LOG3(("Http2Session::ALPNCallback Mandatory Cipher Suite Unavailable\n"));
+      return false;
+    }
+
     if (version >= nsISSLSocketControl::TLS_VERSION_1_2) {
       return true;
     }
diff --git a/netwerk/test/unit/test_http2.js b/netwerk/test/unit/test_http2.js
index 2990c8214e71..5db8b2624ed0 100644
--- a/netwerk/test/unit/test_http2.js
+++ b/netwerk/test/unit/test_http2.js
@@ -789,15 +789,29 @@ WrongSuiteListener.prototype = new Http2CheckListener();
 WrongSuiteListener.prototype.shouldBeHttp2 = false;
 WrongSuiteListener.prototype.onStopRequest = function(request, ctx, status) {
   prefs.setBoolPref("security.ssl3.ecdhe_rsa_aes_128_gcm_sha256", true);
+  prefs.clearUserPref("security.tls.version.max");
   Http2CheckListener.prototype.onStopRequest.call(this);
 };
 
-// test that we use h1 without the mandatory cipher suite available
-function test_http2_wrongsuite() {
+// test that we use h1 without the mandatory cipher suite available when
+// offering at most tls1.2
+function test_http2_wrongsuite_tls12() {
+  prefs.setBoolPref("security.ssl3.ecdhe_rsa_aes_128_gcm_sha256", false);
+  prefs.setIntPref("security.tls.version.max", 3);
+  var chan = makeChan("https://localhost:" + serverPort + "/wrongsuite");
+  chan.loadFlags = Ci.nsIRequest.LOAD_FRESH_CONNECTION | Ci.nsIChannel.LOAD_INITIAL_DOCUMENT_URI;
+  var listener = new WrongSuiteListener();
+  chan.asyncOpen2(listener);
+}
+
+// test that we use h2 when offering tls1.3 or higher regardless of if the
+// mandatory cipher suite is available
+function test_http2_wrongsuite_tls13() {
   prefs.setBoolPref("security.ssl3.ecdhe_rsa_aes_128_gcm_sha256", false);
   var chan = makeChan("https://localhost:" + serverPort + "/wrongsuite");
   chan.loadFlags = Ci.nsIRequest.LOAD_FRESH_CONNECTION | Ci.nsIChannel.LOAD_INITIAL_DOCUMENT_URI;
   var listener = new WrongSuiteListener();
+  listener.shouldBeHttp2 = true;
   chan.asyncOpen2(listener);
 }
 
@@ -1145,7 +1159,8 @@ var tests = [ test_http2_post_big
             , test_http2_h11required_stream
             , test_http2_h11required_session
             , test_http2_retry_rst
-            , test_http2_wrongsuite
+            , test_http2_wrongsuite_tls12
+            , test_http2_wrongsuite_tls13
             , test_http2_push_firstparty1
             , test_http2_push_firstparty2
             , test_http2_push_firstparty3
diff --git a/python/mozlint/mozlint/__init__.py b/python/mozlint/mozlint/__init__.py
index 5b4ec3addbe6..88bc3569b3fb 100644
--- a/python/mozlint/mozlint/__init__.py
+++ b/python/mozlint/mozlint/__init__.py
@@ -6,4 +6,4 @@
 from __future__ import absolute_import
 
 from .roller import LintRoller
-from .result import ResultContainer
+from .result import Issue
diff --git a/python/mozlint/mozlint/cli.py b/python/mozlint/mozlint/cli.py
index 07c10adcf914..c8a8278ecfb3 100644
--- a/python/mozlint/mozlint/cli.py
+++ b/python/mozlint/mozlint/cli.py
@@ -147,7 +147,7 @@ def find_linters(linters=None):
 def run(paths, linters, fmt, outgoing, workdir, edit,
         setup=False, list_linters=False, **lintargs):
     from mozlint import LintRoller, formatters
-    from mozlint.editor import edit_results
+    from mozlint.editor import edit_issues
 
     if list_linters:
         lint_paths = find_linters(linters)
@@ -165,21 +165,20 @@ def run(paths, linters, fmt, outgoing, workdir, edit,
         return ret
 
     # run all linters
-    results = lint.roll(paths, outgoing=outgoing, workdir=workdir)
+    result = lint.roll(paths, outgoing=outgoing, workdir=workdir)
 
-    if edit and results:
-        edit_results(results)
-        results = lint.roll(results.keys())
+    if edit and result.issues:
+        edit_issues(result.issues)
+        result = lint.roll(result.issues.keys())
 
     formatter = formatters.get(fmt)
 
     # Encode output with 'replace' to avoid UnicodeEncodeErrors on
     # environments that aren't using utf-8.
-    out = formatter(results, failed=lint.failed | lint.failed_setup).encode(
-                    sys.stdout.encoding or 'ascii', 'replace')
+    out = formatter(result).encode(sys.stdout.encoding or 'ascii', 'replace')
     if out:
         print(out)
-    return 1 if results or lint.failed else 0
+    return result.returncode
 
 
 if __name__ == '__main__':
diff --git a/python/mozlint/mozlint/editor.py b/python/mozlint/mozlint/editor.py
index aa68fec13137..1b7193b546cc 100644
--- a/python/mozlint/mozlint/editor.py
+++ b/python/mozlint/mozlint/editor.py
@@ -15,8 +15,8 @@ def get_editor():
     return os.environ.get('EDITOR')
 
 
-def edit_results(results):
-    if not results:
+def edit_issues(issues):
+    if not issues:
         return
 
     editor = get_editor()
@@ -41,7 +41,7 @@ def edit_results(results):
         ]
 
         with tempfile.NamedTemporaryFile() as fh:
-            s = formatters.get('compact', summary=False)(results)
+            s = formatters.get('compact', summary=False)(issues)
             fh.write(s)
             fh.flush()
 
@@ -49,5 +49,5 @@ def edit_results(results):
             subprocess.call(cmd)
 
     else:
-        for path, errors in results.iteritems():
+        for path, errors in issues.iteritems():
             subprocess.call([editor, path])
diff --git a/python/mozlint/mozlint/formatters/__init__.py b/python/mozlint/mozlint/formatters/__init__.py
index 6c4aa0ba9fe6..b0ff9aa9b8d9 100644
--- a/python/mozlint/mozlint/formatters/__init__.py
+++ b/python/mozlint/mozlint/formatters/__init__.py
@@ -6,7 +6,7 @@ from __future__ import absolute_import
 
 import json
 
-from ..result import ResultEncoder
+from ..result import IssueEncoder
 from .compact import CompactFormatter
 from .stylish import StylishFormatter
 from .summary import SummaryFormatter
@@ -15,8 +15,8 @@ from .unix import UnixFormatter
 
 
 class JSONFormatter(object):
-    def __call__(self, results, **kwargs):
-        return json.dumps(results, cls=ResultEncoder)
+    def __call__(self, result):
+        return json.dumps(result.issues, cls=IssueEncoder)
 
 
 all_formatters = {
diff --git a/python/mozlint/mozlint/formatters/compact.py b/python/mozlint/mozlint/formatters/compact.py
index 405f2a2642c4..738b9b67ef0b 100644
--- a/python/mozlint/mozlint/formatters/compact.py
+++ b/python/mozlint/mozlint/formatters/compact.py
@@ -4,7 +4,7 @@
 
 from __future__ import absolute_import, unicode_literals
 
-from ..result import ResultContainer
+from ..result import Issue
 
 
 class CompactFormatter(object):
@@ -19,13 +19,13 @@ class CompactFormatter(object):
     def __init__(self, summary=True):
         self.summary = summary
 
-    def __call__(self, result, **kwargs):
+    def __call__(self, result):
         message = []
         num_problems = 0
-        for path, errors in sorted(result.iteritems()):
+        for path, errors in sorted(result.issues.iteritems()):
             num_problems += len(errors)
             for err in errors:
-                assert isinstance(err, ResultContainer)
+                assert isinstance(err, Issue)
 
                 d = {s: getattr(err, s) for s in err.__slots__}
                 d["column"] = ", col %s" % d["column"] if d["column"] else ""
diff --git a/python/mozlint/mozlint/formatters/stylish.py b/python/mozlint/mozlint/formatters/stylish.py
index 3dbca559df56..0aa670e99c66 100644
--- a/python/mozlint/mozlint/formatters/stylish.py
+++ b/python/mozlint/mozlint/formatters/stylish.py
@@ -6,7 +6,7 @@ from __future__ import absolute_import, unicode_literals
 
 from mozterm import Terminal
 
-from ..result import ResultContainer
+from ..result import Issue
 
 
 class StylishFormatter(object):
@@ -54,19 +54,19 @@ class StylishFormatter(object):
             s += 's'
         return str(num) + ' ' + s
 
-    def __call__(self, result, failed=None, **kwargs):
+    def __call__(self, result):
         message = []
-        failed = failed or []
+        failed = result.failed
 
         num_errors = 0
         num_warnings = 0
-        for path, errors in sorted(result.iteritems()):
+        for path, errors in sorted(result.issues.iteritems()):
             self._reset_max()
 
             message.append(self.term.underline(path))
             # Do a first pass to calculate required padding
             for err in errors:
-                assert isinstance(err, ResultContainer)
+                assert isinstance(err, Issue)
                 self._update_max(err)
                 if err.level == 'error':
                     num_errors += 1
diff --git a/python/mozlint/mozlint/formatters/summary.py b/python/mozlint/mozlint/formatters/summary.py
index 65cc3e16cec1..cd7bdb63baa2 100644
--- a/python/mozlint/mozlint/formatters/summary.py
+++ b/python/mozlint/mozlint/formatters/summary.py
@@ -15,12 +15,12 @@ class SummaryFormatter(object):
     def __init__(self, depth=None):
         self.depth = depth or int(os.environ.get('MOZLINT_SUMMARY_DEPTH', 1))
 
-    def __call__(self, result, **kwargs):
-        commonprefix = mozpath.commonprefix([mozpath.abspath(p) for p in result])
+    def __call__(self, result):
+        commonprefix = mozpath.commonprefix([mozpath.abspath(p) for p in result.issues])
         commonprefix = commonprefix.rsplit('/', 1)[0] + '/'
 
         summary = defaultdict(int)
-        for path, errors in result.iteritems():
+        for path, errors in result.issues.iteritems():
             path = mozpath.abspath(path)
             assert path.startswith(commonprefix)
 
diff --git a/python/mozlint/mozlint/formatters/treeherder.py b/python/mozlint/mozlint/formatters/treeherder.py
index 1b152673dbcf..aac0b79e7374 100644
--- a/python/mozlint/mozlint/formatters/treeherder.py
+++ b/python/mozlint/mozlint/formatters/treeherder.py
@@ -4,7 +4,7 @@
 
 from __future__ import absolute_import, unicode_literals
 
-from ..result import ResultContainer
+from ..result import Issue
 
 
 class TreeherderFormatter(object):
@@ -16,11 +16,11 @@ class TreeherderFormatter(object):
     """
     fmt = "TEST-UNEXPECTED-{level} | {path}:{lineno}{column} | {message} ({rule})"
 
-    def __call__(self, result, **kwargs):
+    def __call__(self, result):
         message = []
-        for path, errors in sorted(result.iteritems()):
+        for path, errors in sorted(result.issues.iteritems()):
             for err in errors:
-                assert isinstance(err, ResultContainer)
+                assert isinstance(err, Issue)
 
                 d = {s: getattr(err, s) for s in err.__slots__}
                 d["column"] = ":%s" % d["column"] if d["column"] else ""
diff --git a/python/mozlint/mozlint/formatters/unix.py b/python/mozlint/mozlint/formatters/unix.py
index 4e4b30c2e9d2..b910cd88504b 100644
--- a/python/mozlint/mozlint/formatters/unix.py
+++ b/python/mozlint/mozlint/formatters/unix.py
@@ -6,7 +6,7 @@ from __future__ import absolute_import, unicode_literals
 
 import os
 
-from ..result import ResultContainer
+from ..result import Issue
 
 
 class UnixFormatter(object):
@@ -17,12 +17,12 @@ class UnixFormatter(object):
     """
     fmt = "{path}:{lineno}:{column} {rule} {level}: {message}"
 
-    def __call__(self, result, **kwargs):
+    def __call__(self, result):
         msg = []
 
-        for path, errors in sorted(result.iteritems()):
+        for path, errors in sorted(result.issues.iteritems()):
             for err in errors:
-                assert isinstance(err, ResultContainer)
+                assert isinstance(err, Issue)
 
                 slots = {s: getattr(err, s) for s in err.__slots__}
                 slots["path"] = os.path.relpath(slots["path"])
diff --git a/python/mozlint/mozlint/result.py b/python/mozlint/mozlint/result.py
index 753a72121866..12e825fe2745 100644
--- a/python/mozlint/mozlint/result.py
+++ b/python/mozlint/mozlint/result.py
@@ -4,11 +4,42 @@
 
 from __future__ import absolute_import
 
+from collections import defaultdict
 from json import dumps, JSONEncoder
 
 
-class ResultContainer(object):
-    """Represents a single lint error and its related metadata.
+class ResultSummary(object):
+    """Represents overall result state from an entire lint run."""
+
+    def __init__(self):
+        self.reset()
+
+    def reset(self):
+        self.issues = defaultdict(list)
+        self.failed_run = set()
+        self.failed_setup = set()
+
+    @property
+    def returncode(self):
+        if self.issues or self.failed:
+            return 1
+        return 0
+
+    @property
+    def failed(self):
+        return self.failed_setup | self.failed_run
+
+    def update(self, other):
+        """Merge results from another ResultSummary into this one."""
+        for path, obj in other.issues.items():
+            self.issues[path].extend(obj)
+
+        self.failed_run |= other.failed_run
+        self.failed_setup |= other.failed_setup
+
+
+class Issue(object):
+    """Represents a single lint issue and its related metadata.
 
     :param linter: name of the linter that flagged this error
     :param path: path to the file containing the error
@@ -50,35 +81,36 @@ class ResultContainer(object):
         self.lineoffset = lineoffset
 
     def __repr__(self):
-        s = dumps(self, cls=ResultEncoder, indent=2)
-        return "ResultContainer({})".format(s)
+        s = dumps(self, cls=IssueEncoder, indent=2)
+        return "Issue({})".format(s)
 
 
-class ResultEncoder(JSONEncoder):
-    """Class for encoding :class:`~result.ResultContainer`s to json.
+class IssueEncoder(JSONEncoder):
+    """Class for encoding :class:`~result.Issue`s to json.
 
     Usage:
 
-        json.dumps(results, cls=ResultEncoder)
+        json.dumps(results, cls=IssueEncoder)
     """
+
     def default(self, o):
-        if isinstance(o, ResultContainer):
+        if isinstance(o, Issue):
             return {a: getattr(o, a) for a in o.__slots__}
         return JSONEncoder.default(self, o)
 
 
 def from_config(config, **kwargs):
-    """Create a :class:`~result.ResultContainer` from a linter config.
+    """Create a :class:`~result.Issue` from a linter config.
 
     Convenience method that pulls defaults from a linter
     config and forwards them.
 
     :param config: linter config as defined in a .yml file
-    :param kwargs: same as :class:`~result.ResultContainer`
-    :returns: :class:`~result.ResultContainer` object
+    :param kwargs: same as :class:`~result.Issue`
+    :returns: :class:`~result.Issue` object
     """
     attrs = {}
-    for attr in ResultContainer.__slots__:
+    for attr in Issue.__slots__:
         attrs[attr] = kwargs.get(attr, config.get(attr))
 
     if not attrs['linter']:
@@ -87,4 +119,4 @@ def from_config(config, **kwargs):
     if not attrs['message']:
         attrs['message'] = config.get('description')
 
-    return ResultContainer(**attrs)
+    return Issue(**attrs)
diff --git a/python/mozlint/mozlint/roller.py b/python/mozlint/mozlint/roller.py
index dac3619fff94..ca018fdfdd41 100644
--- a/python/mozlint/mozlint/roller.py
+++ b/python/mozlint/mozlint/roller.py
@@ -8,7 +8,6 @@ import os
 import signal
 import sys
 import traceback
-from collections import defaultdict
 from concurrent.futures import ProcessPoolExecutor
 from math import ceil
 from multiprocessing import cpu_count
@@ -21,6 +20,7 @@ from mozversioncontrol import get_repository_object, MissingUpstreamRepo, Invali
 from .errors import LintersNotConfigured
 from .parser import Parser
 from .pathutils import findobject
+from .result import ResultSummary
 from .types import supported_types
 
 SHUTDOWN = False
@@ -28,11 +28,10 @@ orig_sigint = signal.getsignal(signal.SIGINT)
 
 
 def _run_worker(config, paths, **lintargs):
-    results = defaultdict(list)
-    failed = []
+    result = ResultSummary()
 
     if SHUTDOWN:
-        return results, failed
+        return result
 
     func = supported_types[config['type']]
     try:
@@ -41,17 +40,17 @@ def _run_worker(config, paths, **lintargs):
         traceback.print_exc()
         res = 1
     except (KeyboardInterrupt, SystemExit):
-        return results, failed
+        return result
     finally:
         sys.stdout.flush()
 
     if not isinstance(res, (list, tuple)):
         if res:
-            failed.append(config['name'])
+            result.failed_run.add(config['name'])
     else:
         for r in res:
-            results[r.path].append(r)
-    return results, failed
+            result.issues[r.path].append(r)
+    return result
 
 
 class InterruptableQueue(Queue):
@@ -102,9 +101,7 @@ class LintRoller(object):
         self.lintargs['root'] = root
 
         # result state
-        self.failed = None
-        self.failed_setup = None
-        self.results = None
+        self.result = ResultSummary()
 
         self.root = root
 
@@ -124,7 +121,6 @@ class LintRoller(object):
         if not self.linters:
             raise LintersNotConfigured
 
-        self.failed_setup = set()
         for linter in self.linters:
             if 'setup' not in linter:
                 continue
@@ -136,12 +132,12 @@ class LintRoller(object):
                 res = 1
 
             if res:
-                self.failed_setup.add(linter['name'])
+                self.result.failed_setup.add(linter['name'])
 
-        if self.failed_setup:
+        if self.result.failed_setup:
             print("error: problem with lint setup, skipping {}".format(
-                    ', '.join(sorted(self.failed_setup))))
-            self.linters = [l for l in self.linters if l['name'] not in self.failed_setup]
+                    ', '.join(sorted(self.result.failed_setup))))
+            self.linters = [l for l in self.linters if l['name'] not in self.result.failed_setup]
             return 1
         return 0
 
@@ -168,11 +164,8 @@ class LintRoller(object):
         if future.cancelled():
             return
 
-        results, failed = future.result()
-        if failed:
-            self.failed.update(set(failed))
-        for k, v in results.iteritems():
-            self.results[k].extend(v)
+        # Merge this job's results with our global ones.
+        self.result.update(future.result())
 
     def roll(self, paths=None, outgoing=None, workdir=None, num_procs=None):
         """Run all of the registered linters against the specified file paths.
@@ -182,14 +175,12 @@ class LintRoller(object):
         :param workdir: Lint all files touched in the working directory.
         :param num_procs: The number of processes to use. Default: cpu count
         :return: A dictionary with file names as the key, and a list of
-                 :class:`~result.ResultContainer`s as the value.
+                 :class:`~result.Issue`s as the value.
         """
         if not self.linters:
             raise LintersNotConfigured
 
-        # reset result state
-        self.results = defaultdict(list)
-        self.failed = set()
+        self.result.reset()
 
         # Need to use a set in case vcs operations specify the same file
         # more than once.
@@ -262,4 +253,4 @@ class LintRoller(object):
         signal.signal(signal.SIGINT, _parent_sigint_handler)
         executor.shutdown()
         signal.signal(signal.SIGINT, orig_sigint)
-        return self.results
+        return self.result
diff --git a/python/mozlint/mozlint/types.py b/python/mozlint/mozlint/types.py
index c5cde17b91a2..31b9536f1ac3 100644
--- a/python/mozlint/mozlint/types.py
+++ b/python/mozlint/mozlint/types.py
@@ -29,7 +29,7 @@ class BaseType(object):
         :param config: Linter config the paths are being linted against.
         :param lintargs: External arguments to the linter not defined in
                          the definition, but passed in by a consumer.
-        :returns: A list of :class:`~result.ResultContainer` objects.
+        :returns: A list of :class:`~result.Issue` objects.
         """
         paths = filterpaths(paths, config, **lintargs)
         if not paths:
@@ -112,7 +112,7 @@ class ExternalType(BaseType):
     """Linter type that runs an external function.
 
     The function is responsible for properly formatting the results
-    into a list of :class:`~result.ResultContainer` objects.
+    into a list of :class:`~result.Issue` objects.
     """
     batch = True
 
diff --git a/python/mozlint/test/test_formatters.py b/python/mozlint/test/test_formatters.py
index 524a5f4bcf41..b2402645ab67 100644
--- a/python/mozlint/test/test_formatters.py
+++ b/python/mozlint/test/test_formatters.py
@@ -6,13 +6,12 @@ from __future__ import absolute_import, unicode_literals
 
 import json
 import os
-from collections import defaultdict
 
 import mozunit
 import mozpack.path as mozpath
 import pytest
 
-from mozlint import ResultContainer
+from mozlint.result import Issue, ResultSummary
 from mozlint import formatters
 
 NORMALISED_PATHS = {
@@ -74,15 +73,15 @@ TEST-UNEXPECTED-WARNING | d/e/f.txt:4:2 | oh no bar (bar-not-allowed)
 
 
 @pytest.fixture
-def results(scope='module'):
+def result(scope='module'):
     containers = (
-        ResultContainer(
+        Issue(
             linter='foo',
             path='a/b/c.txt',
             message="oh no foo",
             lineno=1,
         ),
-        ResultContainer(
+        Issue(
             linter='bar',
             path='d/e/f.txt',
             message="oh no bar",
@@ -92,7 +91,7 @@ def results(scope='module'):
             column=2,
             rule="bar-not-allowed",
         ),
-        ResultContainer(
+        Issue(
             linter='baz',
             path='a/b/c.txt',
             message="oh no baz",
@@ -100,26 +99,26 @@ def results(scope='module'):
             source="if baz:",
         ),
     )
-    results = defaultdict(list)
+    result = ResultSummary()
     for c in containers:
-        results[c.path].append(c)
-    return results
+        result.issues[c.path].append(c)
+    return result
 
 
 @pytest.mark.parametrize("name", EXPECTED.keys())
-def test_formatters(results, name):
+def test_formatters(result, name):
     opts = EXPECTED[name]
     fmt = formatters.get(name, **opts['kwargs'])
-    assert fmt(results) == opts['format']
+    assert fmt(result) == opts['format']
 
 
-def test_json_formatter(results):
+def test_json_formatter(result):
     fmt = formatters.get('json')
-    formatted = json.loads(fmt(results))
+    formatted = json.loads(fmt(result))
 
-    assert set(formatted.keys()) == set(results.keys())
+    assert set(formatted.keys()) == set(result.issues.keys())
 
-    slots = ResultContainer.__slots__
+    slots = Issue.__slots__
     for errors in formatted.values():
         for err in errors:
             assert all(s in err for s in slots)
diff --git a/python/mozlint/test/test_roller.py b/python/mozlint/test/test_roller.py
index 3c5b032e7fd5..c35a32db2216 100644
--- a/python/mozlint/test/test_roller.py
+++ b/python/mozlint/test/test_roller.py
@@ -14,8 +14,8 @@ import time
 import mozunit
 import pytest
 
-from mozlint import ResultContainer
 from mozlint.errors import LintersNotConfigured
+from mozlint.result import Issue, ResultSummary
 
 
 here = os.path.abspath(os.path.dirname(__file__))
@@ -32,21 +32,19 @@ def test_roll_no_linters_configured(lint, files):
 def test_roll_successful(lint, linters, files):
     lint.read(linters)
 
-    assert lint.results is None
     result = lint.roll(files)
-    assert len(result) == 1
-    assert lint.results == result
-    assert lint.failed == set([])
+    assert len(result.issues) == 1
+    assert result.failed == set([])
 
-    path = result.keys()[0]
+    path = result.issues.keys()[0]
     assert os.path.basename(path) == 'foobar.js'
 
-    errors = result[path]
+    errors = result.issues[path]
     assert isinstance(errors, list)
     assert len(errors) == 6
 
     container = errors[0]
-    assert isinstance(container, ResultContainer)
+    assert isinstance(container, Issue)
     assert container.rule == 'no-foobar'
 
 
@@ -59,23 +57,27 @@ def test_roll_from_subdir(lint, linters):
 
         # Path relative to cwd works
         result = lint.roll('no_foobar.js')
-        assert len(result) == 0
-        assert len(lint.failed) == 0
+        assert len(result.issues) == 0
+        assert len(result.failed) == 0
+        assert result.returncode == 0
 
         # Path relative to root doesn't work
         result = lint.roll(os.path.join('files', 'no_foobar.js'))
-        assert len(result) == 0
-        assert len(lint.failed) == 3
+        assert len(result.issues) == 0
+        assert len(result.failed) == 3
+        assert result.returncode == 1
 
         # Paths from vcs are always joined to root instead of cwd
         lint.mock_vcs([os.path.join('files', 'no_foobar.js')])
         result = lint.roll(outgoing=True)
-        assert len(result) == 0
-        assert len(lint.failed) == 0
+        assert len(result.issues) == 0
+        assert len(result.failed) == 0
+        assert result.returncode == 0
 
         result = lint.roll(workdir=True)
-        assert len(result) == 0
-        assert len(lint.failed) == 0
+        assert len(result.issues) == 0
+        assert len(result.failed) == 0
+        assert result.returncode == 0
     finally:
         os.chdir(oldcwd)
 
@@ -94,28 +96,29 @@ def test_roll_with_excluded_path(lint, linters, files):
     lint.read(linters)
     result = lint.roll(files)
 
-    assert len(result) == 0
-    assert lint.failed == set([])
+    assert len(result.issues) == 0
+    assert result.failed == set([])
 
 
 def test_roll_with_invalid_extension(lint, lintdir, filedir):
     lint.read(os.path.join(lintdir, 'external.yml'))
     result = lint.roll(os.path.join(filedir, 'foobar.py'))
-    assert len(result) == 0
-    assert lint.failed == set([])
+    assert len(result.issues) == 0
+    assert result.failed == set([])
 
 
 def test_roll_with_failure_code(lint, lintdir, files):
     lint.read(os.path.join(lintdir, 'badreturncode.yml'))
 
-    assert lint.failed is None
     result = lint.roll(files, num_procs=1)
-    assert len(result) == 0
-    assert lint.failed == set(['BadReturnCodeLinter'])
+    assert len(result.issues) == 0
+    assert result.failed == set(['BadReturnCodeLinter'])
 
 
 def fake_run_worker(config, paths, **lintargs):
-    return {'count': [1]}, []
+    result = ResultSummary()
+    result.issues['count'].append(1)
+    return result
 
 
 @pytest.mark.skipif(platform.system() == 'Windows',
@@ -125,7 +128,7 @@ def test_number_of_jobs(monkeypatch, lint, linters, files, num_procs):
     monkeypatch.setattr(sys.modules[lint.__module__], '_run_worker', fake_run_worker)
 
     lint.read(linters)
-    num_jobs = len(lint.roll(files, num_procs=num_procs)['count'])
+    num_jobs = len(lint.roll(files, num_procs=num_procs).issues['count'])
 
     if len(files) >= num_procs:
         assert num_jobs == num_procs * len(linters)
@@ -147,7 +150,7 @@ def test_max_paths_per_job(monkeypatch, lint, linters, files, max_paths, expecte
 
     lint.MAX_PATHS_PER_JOB = max_paths
     lint.read(linters)
-    num_jobs = len(lint.roll(files, num_procs=2)['count'])
+    num_jobs = len(lint.roll(files, num_procs=2).issues['count'])
     assert num_jobs == expected_jobs
 
 
@@ -220,7 +223,7 @@ def test_setup(lint, linters, filedir, capfd):
     assert 'setup failed' in out
     assert 'setup raised' in out
     assert 'error: problem with lint setup, skipping' in out
-    assert lint.failed_setup == set(['SetupFailedLinter', 'SetupRaisedLinter'])
+    assert lint.result.failed_setup == set(['SetupFailedLinter', 'SetupRaisedLinter'])
 
 
 if __name__ == '__main__':
diff --git a/python/mozlint/test/test_types.py b/python/mozlint/test/test_types.py
index 8528f1b3945d..2951f8077f1b 100644
--- a/python/mozlint/test/test_types.py
+++ b/python/mozlint/test/test_types.py
@@ -9,7 +9,7 @@ import os
 import mozunit
 import pytest
 
-from mozlint.result import ResultContainer
+from mozlint.result import Issue, ResultSummary
 
 
 @pytest.fixture
@@ -31,25 +31,26 @@ def linter(lintdir, request):
 def test_linter_types(lint, linter, files, path):
     lint.read(linter)
     result = lint.roll(files)
-    assert isinstance(result, dict)
-    assert path('foobar.js') in result
-    assert path('no_foobar.js') not in result
+    assert isinstance(result, ResultSummary)
+    assert isinstance(result.issues, dict)
+    assert path('foobar.js') in result.issues
+    assert path('no_foobar.js') not in result.issues
 
-    result = result[path('foobar.js')][0]
-    assert isinstance(result, ResultContainer)
+    issue = result.issues[path('foobar.js')][0]
+    assert isinstance(issue, Issue)
 
     name = os.path.basename(linter).split('.')[0]
-    assert result.linter.lower().startswith(name)
+    assert issue.linter.lower().startswith(name)
 
 
 def test_no_filter(lint, lintdir, files):
     lint.read(os.path.join(lintdir, 'explicit_path.yml'))
     result = lint.roll(files)
-    assert len(result) == 0
+    assert len(result.issues) == 0
 
     lint.lintargs['use_filters'] = False
     result = lint.roll(files)
-    assert len(result) == 3
+    assert len(result.issues) == 3
 
 
 if __name__ == '__main__':
diff --git a/servo/components/style/values/specified/svg_path.rs b/servo/components/style/values/specified/svg_path.rs
index 8d92e94aee0c..48ae185477df 100644
--- a/servo/components/style/values/specified/svg_path.rs
+++ b/servo/components/style/values/specified/svg_path.rs
@@ -7,8 +7,8 @@
 use cssparser::Parser;
 use parser::{Parse, ParserContext};
 use std::fmt::{self, Write};
-use std::iter::Peekable;
-use std::str::Chars;
+use std::iter::{Cloned, Peekable};
+use std::slice;
 use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
 use style_traits::values::SequenceWriter;
 use values::CSSFloat;
@@ -133,8 +133,8 @@ impl ToCss for PathCommand {
     {
         use self::PathCommand::*;
         match *self {
-            Unknown => dest.write_str("X"),
-            ClosePath => dest.write_str("Z"),
+            Unknown => dest.write_char('X'),
+            ClosePath => dest.write_char('Z'),
             MoveTo { point, absolute } => {
                 dest.write_char(if absolute { 'M' } else { 'm' })?;
                 dest.write_char(' ')?;
@@ -219,7 +219,7 @@ impl CoordPair {
 
 /// SVG Path parser.
 struct PathParser<'a> {
-    chars: Peekable<Chars<'a>>,
+    chars: Peekable<Cloned<slice::Iter<'a, u8>>>,
     path: Vec<PathCommand>,
 }
 
@@ -256,7 +256,7 @@ impl<'a> PathParser<'a> {
     #[inline]
     fn new(string: &'a str) -> Self {
         PathParser {
-            chars: string.chars().peekable(),
+            chars: string.as_bytes().iter().cloned().peekable(),
             path: Vec::new(),
         }
     }
@@ -270,13 +270,13 @@ impl<'a> PathParser<'a> {
         // Handle other commands.
         loop {
             skip_wsp(&mut self.chars);
-            if self.chars.peek().map_or(true, |m| *m == 'M' || *m == 'm') {
+            if self.chars.peek().map_or(true, |&m| m == b'M' || m == b'm') {
                 break;
             }
 
             match self.chars.next() {
                 Some(command) => {
-                    let abs = command.is_uppercase();
+                    let abs = command.is_ascii_uppercase();
                     macro_rules! parse_command {
                         ( $($($p:pat)|+ => $parse_func:ident,)* ) => {
                             match command {
@@ -291,15 +291,15 @@ impl<'a> PathParser<'a> {
                         }
                     }
                     parse_command!(
-                        'Z' | 'z' => parse_closepath,
-                        'L' | 'l' => parse_lineto,
-                        'H' | 'h' => parse_h_lineto,
-                        'V' | 'v' => parse_v_lineto,
-                        'C' | 'c' => parse_curveto,
-                        'S' | 's' => parse_smooth_curveto,
-                        'Q' | 'q' => parse_quadratic_bezier_curveto,
-                        'T' | 't' => parse_smooth_quadratic_bezier_curveto,
-                        'A' | 'a' => parse_elliprical_arc,
+                        b'Z' | b'z' => parse_closepath,
+                        b'L' | b'l' => parse_lineto,
+                        b'H' | b'h' => parse_h_lineto,
+                        b'V' | b'v' => parse_v_lineto,
+                        b'C' | b'c' => parse_curveto,
+                        b'S' | b's' => parse_smooth_curveto,
+                        b'Q' | b'q' => parse_quadratic_bezier_curveto,
+                        b'T' | b't' => parse_smooth_quadratic_bezier_curveto,
+                        b'A' | b'a' => parse_elliprical_arc,
                     );
                 },
                 _ => break, // no more commands.
@@ -311,13 +311,13 @@ impl<'a> PathParser<'a> {
     /// Parse "moveto" command.
     fn parse_moveto(&mut self) -> Result<(), ()> {
         let command = match self.chars.next() {
-            Some(c) if c == 'M' || c == 'm' => c,
+            Some(c) if c == b'M' || c == b'm' => c,
             _ => return Err(()),
         };
 
         skip_wsp(&mut self.chars);
         let point = parse_coord(&mut self.chars)?;
-        let absolute = command == 'M';
+        let absolute = command == b'M';
         self.path.push(PathCommand::MoveTo { point, absolute } );
 
         // End of string or the next character is a possible new command.
@@ -382,13 +382,11 @@ impl<'a> PathParser<'a> {
     /// Parse elliptical arc curve command.
     fn parse_elliprical_arc(&mut self, absolute: bool) -> Result<(), ()> {
         // Parse a flag whose value is '0' or '1'; otherwise, return Err(()).
-        let parse_flag = |iter: &mut Peekable<Chars>| -> Result<bool, ()> {
-            let value = match iter.peek() {
-                Some(c) if *c == '0' || *c == '1' => *c == '1',
-                _ => return Err(()),
-            };
-            iter.next();
-            Ok(value)
+        let parse_flag = |iter: &mut Peekable<Cloned<slice::Iter<u8>>>| -> Result<bool, ()> {
+            match iter.next() {
+                Some(c) if c == b'0' || c == b'1' => Ok(c == b'1'),
+                _ => Err(()),
+            }
         };
         parse_arguments!(self, absolute, EllipticalArc, [
             rx => parse_number,
@@ -403,7 +401,7 @@ impl<'a> PathParser<'a> {
 
 
 /// Parse a pair of numbers into CoordPair.
-fn parse_coord(iter: &mut Peekable<Chars>) -> Result<CoordPair, ()> {
+fn parse_coord(iter: &mut Peekable<Cloned<slice::Iter<u8>>>) -> Result<CoordPair, ()> {
     let x = parse_number(iter)?;
     skip_comma_wsp(iter);
     let y = parse_number(iter)?;
@@ -417,28 +415,28 @@ fn parse_coord(iter: &mut Peekable<Chars>) -> Result<CoordPair, ()> {
 /// input is a Peekable and we only accept an integer of a floating point number.
 ///
 /// The "number" syntax in https://www.w3.org/TR/SVG/paths.html#PathDataBNF
-fn parse_number(iter: &mut Peekable<Chars>) -> Result<CSSFloat, ()> {
+fn parse_number(iter: &mut Peekable<Cloned<slice::Iter<u8>>>) -> Result<CSSFloat, ()> {
     // 1. Check optional sign.
-    let sign = if iter.peek().map_or(false, |&sign: &char| sign == '+' || sign == '-') {
-        if iter.next().unwrap() == '-' { -1. } else { 1. }
+    let sign = if iter.peek().map_or(false, |&sign| sign == b'+' || sign == b'-') {
+        if iter.next().unwrap() == b'-' { -1. } else { 1. }
     } else {
         1.
     };
 
     // 2. Check integer part.
     let mut integral_part: f64 = 0.;
-    let got_dot = if !iter.peek().map_or(false, |&n: &char| n == '.') {
+    let got_dot = if !iter.peek().map_or(false, |&n| n == b'.') {
         // If the first digit in integer part is neither a dot nor a digit, this is not a number.
-        if iter.peek().map_or(true, |n: &char| !n.is_ascii_digit()) {
+        if iter.peek().map_or(true, |n| !n.is_ascii_digit()) {
             return Err(());
         }
 
-        while iter.peek().map_or(false, |n: &char| n.is_ascii_digit()) {
+        while iter.peek().map_or(false, |n| n.is_ascii_digit()) {
             integral_part =
-                integral_part * 10. + iter.next().unwrap().to_digit(10).unwrap() as f64;
+                integral_part * 10. + (iter.next().unwrap() - b'0') as f64;
         }
 
-        iter.peek().map_or(false, |&n: &char| n == '.')
+        iter.peek().map_or(false, |&n| n == b'.')
     } else {
         true
     };
@@ -449,13 +447,13 @@ fn parse_number(iter: &mut Peekable<Chars>) -> Result<CSSFloat, ()> {
         // Consume '.'.
         iter.next();
         // If the first digit in fractional part is not a digit, this is not a number.
-        if iter.peek().map_or(true, |n: &char| !n.is_ascii_digit()) {
+        if iter.peek().map_or(true, |n| !n.is_ascii_digit()) {
             return Err(());
         }
 
         let mut factor = 0.1;
-        while iter.peek().map_or(false, |n: &char| n.is_ascii_digit()) {
-            fractional_part += iter.next().unwrap().to_digit(10).unwrap() as f64 * factor;
+        while iter.peek().map_or(false, |n| n.is_ascii_digit()) {
+            fractional_part += (iter.next().unwrap() - b'0') as f64 * factor;
             factor *= 0.1;
         }
     }
@@ -464,18 +462,18 @@ fn parse_number(iter: &mut Peekable<Chars>) -> Result<CSSFloat, ()> {
 
     // 4. Check exp part. The segment name of SVG Path doesn't include 'E' or 'e', so it's ok to
     //    treat the numbers after 'E' or 'e' are in the exponential part.
-    if iter.peek().map_or(false, |&exp: &char| exp == 'E' || exp == 'e') {
+    if iter.peek().map_or(false, |&exp| exp == b'E' || exp == b'e') {
         // Consume 'E' or 'e'.
         iter.next();
-        let exp_sign = if iter.peek().map_or(false, |&sign: &char| sign == '+' || sign == '-') {
-            if iter.next().unwrap() == '-' { -1. } else { 1. }
+        let exp_sign = if iter.peek().map_or(false, |&sign| sign == b'+' || sign == b'-') {
+            if iter.next().unwrap() == b'-' { -1. } else { 1. }
         } else {
             1.
         };
 
         let mut exp: f64 = 0.;
-        while iter.peek().map_or(false, |n: &char| n.is_ascii_digit()) {
-            exp = exp * 10. + iter.next().unwrap().to_digit(10).unwrap() as f64;
+        while iter.peek().map_or(false, |n| n.is_ascii_digit()) {
+            exp = exp * 10. + (iter.next().unwrap() - b'0') as f64;
         }
 
         value *= f64::powf(10., exp * exp_sign);
@@ -490,12 +488,12 @@ fn parse_number(iter: &mut Peekable<Chars>) -> Result<CSSFloat, ()> {
 
 /// Skip all svg whitespaces, and return true if |iter| hasn't finished.
 #[inline]
-fn skip_wsp(iter: &mut Peekable<Chars>) -> bool {
+fn skip_wsp(iter: &mut Peekable<Cloned<slice::Iter<u8>>>) -> bool {
     // Note: SVG 1.1 defines the whitespaces as \u{9}, \u{20}, \u{A}, \u{D}.
     //       However, SVG 2 has one extra whitespace: \u{C}.
     //       Therefore, we follow the newest spec for the definition of whitespace,
-    //       i.e. \u{9}, \u{20}, \u{A}, \u{C}, \u{D}, by is_ascii_whitespace().
-    while iter.peek().map_or(false, |c: &char| c.is_ascii_whitespace()) {
+    //       i.e. \u{9}, \u{20}, \u{A}, \u{C}, \u{D}.
+    while iter.peek().map_or(false, |c| c.is_ascii_whitespace()) {
         iter.next();
     }
     iter.peek().is_some()
@@ -503,12 +501,12 @@ fn skip_wsp(iter: &mut Peekable<Chars>) -> bool {
 
 /// Skip all svg whitespaces and one comma, and return true if |iter| hasn't finished.
 #[inline]
-fn skip_comma_wsp(iter: &mut Peekable<Chars>) -> bool {
+fn skip_comma_wsp(iter: &mut Peekable<Cloned<slice::Iter<u8>>>) -> bool {
     if !skip_wsp(iter) {
         return false;
     }
 
-    if *iter.peek().unwrap() != ',' {
+    if *iter.peek().unwrap() != b',' {
         return true;
     }
     iter.next();
diff --git a/servo/support/gecko/nsstring/src/conversions.rs b/servo/support/gecko/nsstring/src/conversions.rs
index 0a3f3ceea780..8598f41c07c5 100644
--- a/servo/support/gecko/nsstring/src/conversions.rs
+++ b/servo/support/gecko/nsstring/src/conversions.rs
@@ -139,10 +139,10 @@ macro_rules! constant_conversion {
     (name = $name:ident,
      convert = $convert:ident,
      other_ty = $other_ty:ty) => (
-        fn $name(&mut self, other: $other_ty, old_len: usize) -> Result<BulkWriteOk, ()> {
+        fn $name(&mut self, other: $other_ty, old_len: usize, allow_shrinking: bool) -> Result<BulkWriteOk, ()> {
             let new_len = old_len.checked_add(other.len()).ok_or(())?;
             let mut handle = unsafe {
-                self.bulk_write(new_len, old_len, true)?
+                self.bulk_write(new_len, old_len, allow_shrinking)?
             };
             $convert(other, &mut handle.as_mut_slice()[old_len..]);
             Ok(handle.finish(new_len, false))
@@ -281,7 +281,7 @@ impl nsAString {
     /// Convert a Latin1 (i.e. byte value equals scalar value; not windows-1252!)
     /// into UTF-16 and replace the content of this string with the conversion result.
     pub fn assign_latin1(&mut self, other: &[u8]) {
-        self.fallible_append_latin1_impl(other, 0)
+        self.fallible_append_latin1_impl(other, 0, true)
             .expect("Out of memory");
     }
 
@@ -289,14 +289,14 @@ impl nsAString {
     /// into UTF-16 and fallibly replace the content of this string with the
     /// conversion result.
     pub fn fallible_assign_latin1(&mut self, other: &[u8]) -> Result<(), ()> {
-        self.fallible_append_latin1_impl(other, 0).map(|_| ())
+        self.fallible_append_latin1_impl(other, 0, true).map(|_| ())
     }
 
     /// Convert a Latin1 (i.e. byte value equals scalar value; not windows-1252!)
     /// into UTF-16 and append the conversion result to this string.
     pub fn append_latin1(&mut self, other: &[u8]) {
         let len = self.len();
-        self.fallible_append_latin1_impl(other, len)
+        self.fallible_append_latin1_impl(other, len, false)
             .expect("Out of memory");
     }
 
@@ -304,7 +304,7 @@ impl nsAString {
     /// into UTF-16 and fallibly append the conversion result to this string.
     pub fn fallible_append_latin1(&mut self, other: &[u8]) -> Result<(), ()> {
         let len = self.len();
-        self.fallible_append_latin1_impl(other, len).map(|_| ())
+        self.fallible_append_latin1_impl(other, len, false).map(|_| ())
     }
 }
 
@@ -415,7 +415,7 @@ impl nsACString {
     /// release builds. The nature of the garbage may differ based on CPU
     /// architecture and must not be relied upon.
     pub fn assign_utf16_to_latin1_lossy(&mut self, other: &[u16]) {
-        self.fallible_append_utf16_to_latin1_lossy_impl(other, 0)
+        self.fallible_append_utf16_to_latin1_lossy_impl(other, 0, true)
             .expect("Out of memory");
     }
 
@@ -430,7 +430,7 @@ impl nsACString {
     /// release builds. The nature of the garbage may differ based on CPU
     /// architecture and must not be relied upon.
     pub fn fallible_assign_utf16_to_latin1_lossy(&mut self, other: &[u16]) -> Result<(), ()> {
-        self.fallible_append_utf16_to_latin1_lossy_impl(other, 0)
+        self.fallible_append_utf16_to_latin1_lossy_impl(other, 0, true)
             .map(|_| ())
     }
 
@@ -446,7 +446,7 @@ impl nsACString {
     /// architecture and must not be relied upon.
     pub fn append_utf16_to_latin1_lossy(&mut self, other: &[u16]) {
         let len = self.len();
-        self.fallible_append_utf16_to_latin1_lossy_impl(other, len)
+        self.fallible_append_utf16_to_latin1_lossy_impl(other, len, false)
             .expect("Out of memory");
     }
 
@@ -462,7 +462,7 @@ impl nsACString {
     /// architecture and must not be relied upon.
     pub fn fallible_append_utf16_to_latin1_lossy(&mut self, other: &[u16]) -> Result<(), ()> {
         let len = self.len();
-        self.fallible_append_utf16_to_latin1_lossy_impl(other, len)
+        self.fallible_append_utf16_to_latin1_lossy_impl(other, len, false)
             .map(|_| ())
     }
 
@@ -692,10 +692,11 @@ pub unsafe extern "C" fn nsstring_fallible_append_latin1_impl(
     other: *const u8,
     other_len: usize,
     old_len: usize,
+    allow_shrinking: bool,
 ) -> bool {
     let other_slice = slice::from_raw_parts(other, other_len);
     (*this)
-        .fallible_append_latin1_impl(other_slice, old_len)
+        .fallible_append_latin1_impl(other_slice, old_len, allow_shrinking)
         .is_ok()
 }
 
@@ -718,10 +719,11 @@ pub unsafe extern "C" fn nscstring_fallible_append_utf16_to_latin1_lossy_impl(
     other: *const u16,
     other_len: usize,
     old_len: usize,
+    allow_shrinking: bool,
 ) -> bool {
     let other_slice = slice::from_raw_parts(other, other_len);
     (*this)
-        .fallible_append_utf16_to_latin1_lossy_impl(other_slice, old_len)
+        .fallible_append_utf16_to_latin1_lossy_impl(other_slice, old_len, allow_shrinking)
         .is_ok()
 }
 
diff --git a/taskcluster/docker/funsize-update-generator/Pipfile.lock b/taskcluster/docker/funsize-update-generator/Pipfile.lock
index 928f055f34c7..cb16c4ccd5ce 100644
--- a/taskcluster/docker/funsize-update-generator/Pipfile.lock
+++ b/taskcluster/docker/funsize-update-generator/Pipfile.lock
@@ -18,24 +18,31 @@
     "default": {
         "aiohttp": {
             "hashes": [
-                "sha256:1a112a1fdf3802b7f2b182e22e51d71e4a8fa7387d0d38e79a268921b869e384",
-                "sha256:33aa7c937ebaf063a860cbb0c263a771b33333a84965c6148eeafe64fb4e29ca",
-                "sha256:550b4a0788500f6d00f41b7fdd9fcce6d78f99706a7b2f6f81d4d331c7ca468e",
-                "sha256:601e8e83123b4d423a9dfddf7d6943f4f520651a78ffcd50c99d065136c7ff7b",
-                "sha256:620f19ba7628b70b177f5c2e6a55a6fd6e7c8591cde38c3f8f52551733d31b66",
-                "sha256:70d56c784da1239c89d39fefa166fd429306dada641178389be4184a9c04e501",
-                "sha256:7de2c9e445a5d257935011268202338538abef1aaff341a4733eca56419ca6f6",
-                "sha256:96bb80b659cc2bafa160f3f0c346ce7fc10de1ffec4908d7f9690797f155f658",
-                "sha256:ae7501cc6a6c37b8d4774bf2218c37be47fe42019a2570e8510fc2044e59d573",
-                "sha256:c833aa6f4c9ac3e3eb843e3d999bae51339ad33a937303f43ce78064e61cb4b6",
-                "sha256:dd81d85a342edf3d2a388e2f24d9facebc9c04550043888f970ee2f228c93059",
-                "sha256:f20deec7a3fbaec7b5eb7ad99878427ad2ee4cc16a46732b705e8121cbb3cc12",
-                "sha256:f52e7287eb9286a1e91e4c67c207c2573147fbaddc68f70efb5aeee5d1992f2e",
-                "sha256:fe7b2972ff7e779e812f974aa5695edc328ecf559ceeea887ac46f06f090ad4c",
-                "sha256:ff1447c84a02b9cd5dd3a9332d1fb181a4386c3625765bb5caf1cfbc210ab3f9"
+                "sha256:01a2059a0505460828854d218cf090d80db277033b8e6906144ab9bd4677fc82",
+                "sha256:01bcaf83911c5a88f74629f116540a1b80391e6e496e6fb8708bb2987b60da63",
+                "sha256:199ea4a9c424904f04a86563a8e9e2759d49e3a0bf789496714253237f16015f",
+                "sha256:229975cb8ff6056c8ef581383a653e7110480d52c9f46eaf560113f8d5005510",
+                "sha256:2bb4224e3a3d7dd2ee18f6c42c1925c3200cd46fe18ec9f293b9bc88644c4878",
+                "sha256:2ddf47c31048efad5a566d82822194bbb680fc1be852915c2949eb69891b5d5a",
+                "sha256:3bc9c87845962f583d6929f837b02b80d2544920be65daf0d0a1306ad1a2089b",
+                "sha256:3f88a3428f40c788321cf5b8191f9dd9e002145545fa0cefc023b4b11e17aaa7",
+                "sha256:4785935328facee0878c29d46f02b12f1e8e8db1cd3d9ec9af666eb163418a64",
+                "sha256:48e8d1973ba62a952f19a7916e54a7155f4b14505507432fc0559d8b5b0e5cad",
+                "sha256:5cd8662ddd7c95e99010e30cc52e20a092939844e8e8a4f37abf1866231f1880",
+                "sha256:6880406a0c776fbff63c0d9eb8a2d96d8134b17fafeeea01180b58ab8ff0f6f5",
+                "sha256:6a8e447742fc45791ffea0b3ce308f1476a9f4707fb6525a2f23b43d4b26cfb3",
+                "sha256:81456c04c54288928da4e7e1893314c8e74d5e9f33163e39aa47c26c5e5c7911",
+                "sha256:9b15efa7411dcf3b59c1f4766eb16ba1aba4531a33e54d469ee22106eabce460",
+                "sha256:a6132db365def76145084041cede574a0c8ed53aa1a680a3027e41ee8f291bd4",
+                "sha256:ddee38858a9ef52ca33cb5dd1607d07d0fb99e2efe523ecb437b1758c49622a5",
+                "sha256:de703f333381864dce788dbfa1a49ef4551e8f082b607a943b94b239d97965cc",
+                "sha256:e08cacfede41291c05b4668c3178d303d078417c013bc3d5287b2b0d0e6a3aa7",
+                "sha256:e4c37c7ec1e1157ae4af73fd1d7f201accebf6ed2222120bc660fd002c45cbac",
+                "sha256:e4f9fc91d617d2e54bda97bc1db9814918691fe799e037ccf973fda434fd2c18",
+                "sha256:f6f73c812c1830a06de76ccbea10a4ebb1fd46230a80f280362e84578e4932a2"
             ],
             "index": "pypi",
-            "version": "==3.3.2"
+            "version": "==3.4.0"
         },
         "arrow": {
             "hashes": [
@@ -73,10 +80,10 @@
         },
         "certifi": {
             "hashes": [
-                "sha256:4c1d68a1408dd090d2f3a869aa94c3947cc1d967821d1ed303208c9f41f0f2f4",
-                "sha256:b6e8b28b2b7e771a41ecdd12d4d43262ecab52adebbafa42c77d6b57fb6ad3a4"
+                "sha256:376690d6f16d32f9d1fe8932551d80b23e9d393a8578c5633a2ed39a64861638",
+                "sha256:456048c7e371c089d0a77a5212fb37a2c2dce1e24146e3b7e0261736aaeaa22a"
             ],
-            "version": "==2018.8.13"
+            "version": "==2018.8.24"
         },
         "cffi": {
             "hashes": [
@@ -204,13 +211,14 @@
             "hashes": [
                 "sha256:a933e3bb13da54383f9e8f35dc4f9cb9eb9b3b78c6b36f311254d6d0d92c6c7c"
             ],
+            "markers": "python_version < '3.7'",
             "version": "==1.1.0"
         },
         "json-e": {
             "hashes": [
-                "sha256:fcdb79e0da91466260af9a5a67a25916f02eac66e8f02e8dc3161182bd11c1bc"
+                "sha256:d8c1ec3f5bbc7728c3a504ebe58829f283c64eca230871e4eefe974b4cdaae4a"
             ],
-            "version": "==2.6.0"
+            "version": "==2.7.0"
         },
         "jsonschema": {
             "hashes": [
@@ -370,6 +378,7 @@
                 "sha256:99dd90bc1c566968868c8b07ede32f8e031cbccd52c7195a61e802679d461447",
                 "sha256:d0360063c1a3fcaaa514bb31c03954ba573d2b671df40a2ecfdfd9339cc8e93e"
             ],
+            "markers": "python_version >= '3.5.3'",
             "version": "==4.0.1"
         },
         "urllib3": {
@@ -377,7 +386,7 @@
                 "sha256:a68ac5e15e76e7e5dd2b8f94007233e01effe3e50e8daddf69acfd81cb686baf",
                 "sha256:b5725a0bd4ba422ab0e66e89e030c806576753ea3ee08554382c14e685d117b5"
             ],
-            "markers": "python_version != '3.0.*' and python_version != '3.2.*' and python_version != '3.3.*' and python_version >= '2.6' and python_version < '4' and python_version != '3.1.*'",
+            "markers": "python_version < '4' and python_version >= '2.6' and python_version != '3.2.*' and python_version != '3.1.*' and python_version != '3.3.*' and python_version != '3.0.*'",
             "version": "==1.23"
         },
         "virtualenv": {
@@ -385,7 +394,7 @@
                 "sha256:2ce32cd126117ce2c539f0134eb89de91a8413a29baac49cbab3eb50e2026669",
                 "sha256:ca07b4c0b54e14a91af9f34d0919790b016923d157afda5efdde55c96718f752"
             ],
-            "markers": "python_version >= '2.7' and python_version != '3.1.*' and python_version != '3.0.*' and python_version != '3.2.*'",
+            "markers": "python_version != '3.1.*' and python_version >= '2.7' and python_version != '3.0.*' and python_version != '3.2.*'",
             "version": "==16.0.0"
         },
         "yarl": {
@@ -400,7 +409,6 @@
                 "sha256:f17495e6fe3d377e3faac68121caef6f974fcb9e046bc075bcff40d8e5cc69a4",
                 "sha256:f85900b9cca0c67767bb61b2b9bd53208aaa7373dae633dbe25d179b4bf38aa7"
             ],
-            "markers": "python_version >= '3.4.1'",
             "version": "==1.2.6"
         }
     },
diff --git a/testing/raptor/raptor/tests/raptor-sunspider.ini b/testing/raptor/raptor/tests/raptor-sunspider.ini
index ba0da59f44ac..a2b7384385e5 100644
--- a/testing/raptor/raptor/tests/raptor-sunspider.ini
+++ b/testing/raptor/raptor/tests/raptor-sunspider.ini
@@ -9,8 +9,8 @@ type =  benchmark
 test_url = http://localhost:<port>/SunSpider/sunspider-1.0.1/sunspider-1.0.1/driver.html?raptor
 page_cycles = 5
 page_timeout = 35000
-unit = score
-lower_is_better = false
+unit = ms
+lower_is_better = true
 alert_threshold = 2.0
 
 [raptor-sunspider-firefox]
diff --git a/testing/talos/talos/test.py b/testing/talos/talos/test.py
index 70afa73c77e0..609290aec1c7 100644
--- a/testing/talos/talos/test.py
+++ b/testing/talos/talos/test.py
@@ -428,7 +428,7 @@ class damp(PageloaderTest):
     tploadnocache = True
     tpmozafterpaint = False
     gecko_profile_interval = 10
-    gecko_profile_entries = 1000000
+    gecko_profile_entries = 2000000
     win_counters = w7_counters = linux_counters = mac_counters = None
     filters = filter.ignore_first.prepare(1) + filter.median.prepare()
     preferences = {'devtools.memory.enabled': True,
diff --git a/testing/web-platform/meta/MANIFEST.json b/testing/web-platform/meta/MANIFEST.json
index 833e27d8ee5d..df7c495c9523 100644
--- a/testing/web-platform/meta/MANIFEST.json
+++ b/testing/web-platform/meta/MANIFEST.json
@@ -112915,6 +112915,30 @@
      {}
     ]
    ],
+   "css/css-filter/blur-clip-stacking-context-001.html": [
+    [
+     "/css/css-filter/blur-clip-stacking-context-001.html",
+     [
+      [
+       "/css/css-filter/blur-clip-stacking-context-ref.html",
+       "=="
+      ]
+     ],
+     {}
+    ]
+   ],
+   "css/css-filter/blur-clip-stacking-context-002.html": [
+    [
+     "/css/css-filter/blur-clip-stacking-context-002.html",
+     [
+      [
+       "/css/css-filter/blur-clip-stacking-context-ref.html",
+       "!="
+      ]
+     ],
+     {}
+    ]
+   ],
    "css/css-filter/filtered-block-is-container.html": [
     [
      "/css/css-filter/filtered-block-is-container.html",
@@ -244073,6 +244097,11 @@
      {}
     ]
    ],
+   "css/css-filter/blur-clip-stacking-context-ref.html": [
+    [
+     {}
+    ]
+   ],
    "css/css-filter/filtered-block-is-container-ref.html": [
     [
      {}
@@ -523187,6 +523216,18 @@
    "8d0683319b0fbbd1262cbdd12cdbcb727b2aa9a0",
    "support"
   ],
+  "css/css-filter/blur-clip-stacking-context-001.html": [
+   "48c1bae3042b6912ba5edd7ae74c190e5bd8f2d2",
+   "reftest"
+  ],
+  "css/css-filter/blur-clip-stacking-context-002.html": [
+   "f4df453b17b86a6da67c4cf5f71261e9315eab95",
+   "reftest"
+  ],
+  "css/css-filter/blur-clip-stacking-context-ref.html": [
+   "82b907334fd71791cd2f6530e2e85169e29afa41",
+   "support"
+  ],
   "css/css-filter/filtered-block-is-container-ref.html": [
    "fc9467f8717dfc722dcb6dbbbb31bfd8c2baee3b",
    "support"
diff --git a/testing/web-platform/meta/dom/events/AddEventListenerOptions-passive.html.ini b/testing/web-platform/meta/dom/events/AddEventListenerOptions-passive.html.ini
deleted file mode 100644
index daa2db61f616..000000000000
--- a/testing/web-platform/meta/dom/events/AddEventListenerOptions-passive.html.ini
+++ /dev/null
@@ -1,4 +0,0 @@
-[AddEventListenerOptions-passive.html]
-  [returnValue should be ignored if-and-only-if the passive option is true]
-    expected: FAIL
-
diff --git a/testing/web-platform/meta/dom/events/Event-constructors.html.ini b/testing/web-platform/meta/dom/events/Event-constructors.html.ini
deleted file mode 100644
index 69db3949a539..000000000000
--- a/testing/web-platform/meta/dom/events/Event-constructors.html.ini
+++ /dev/null
@@ -1,7 +0,0 @@
-[Event-constructors.html]
-  [Event constructors 2]
-    expected: FAIL
-
-  [Event constructors 3]
-    expected: FAIL
-
diff --git a/testing/web-platform/meta/dom/events/Event-defaultPrevented-after-dispatch.html.ini b/testing/web-platform/meta/dom/events/Event-defaultPrevented-after-dispatch.html.ini
deleted file mode 100644
index 5187ca566809..000000000000
--- a/testing/web-platform/meta/dom/events/Event-defaultPrevented-after-dispatch.html.ini
+++ /dev/null
@@ -1,4 +0,0 @@
-[Event-defaultPrevented-after-dispatch.html]
-  [Default prevention via returnValue]
-    expected: FAIL
-
diff --git a/testing/web-platform/meta/dom/events/Event-initEvent.html.ini b/testing/web-platform/meta/dom/events/Event-initEvent.html.ini
deleted file mode 100644
index 0b4ce51d9406..000000000000
--- a/testing/web-platform/meta/dom/events/Event-initEvent.html.ini
+++ /dev/null
@@ -1,13 +0,0 @@
-[Event-initEvent.html]
-  [Properties of initEvent(type, true, true)]
-    expected: FAIL
-
-  [Properties of initEvent(type, true, false)]
-    expected: FAIL
-
-  [Properties of initEvent(type, false, true)]
-    expected: FAIL
-
-  [Properties of initEvent(type, false, false)]
-    expected: FAIL
-
diff --git a/testing/web-platform/meta/dom/events/Event-returnValue.html.ini b/testing/web-platform/meta/dom/events/Event-returnValue.html.ini
deleted file mode 100644
index e9c34f6438f4..000000000000
--- a/testing/web-platform/meta/dom/events/Event-returnValue.html.ini
+++ /dev/null
@@ -1,19 +0,0 @@
-[Event-returnValue.html]
-  [When an event is created, returnValue should be initialized to true.]
-    expected: FAIL
-
-  [preventDefault() should not change returnValue if cancelable is false.]
-    expected: FAIL
-
-  [returnValue=false should have no effect if cancelable is false.]
-    expected: FAIL
-
-  [preventDefault() should change returnValue if cancelable is true.]
-    expected: FAIL
-
-  [initEvent should unset returnValue.]
-    expected: FAIL
-
-  [returnValue=true should have no effect once the canceled flag was set.]
-    expected: FAIL
-
diff --git a/testing/web-platform/meta/dom/events/EventTarget-dispatchEvent-returnvalue.html.ini b/testing/web-platform/meta/dom/events/EventTarget-dispatchEvent-returnvalue.html.ini
deleted file mode 100644
index 5fe7e8ffe604..000000000000
--- a/testing/web-platform/meta/dom/events/EventTarget-dispatchEvent-returnvalue.html.ini
+++ /dev/null
@@ -1,7 +0,0 @@
-[EventTarget-dispatchEvent-returnvalue.html]
-  [Return value of EventTarget.dispatchEvent() affected by preventDefault().]
-    expected: FAIL
-
-  [Return value of EventTarget.dispatchEvent() affected by returnValue.]
-    expected: FAIL
-
diff --git a/testing/web-platform/meta/dom/interfaces.html.ini b/testing/web-platform/meta/dom/interfaces.html.ini
index 72558edf059f..e1543cbd5a99 100644
--- a/testing/web-platform/meta/dom/interfaces.html.ini
+++ b/testing/web-platform/meta/dom/interfaces.html.ini
@@ -87,17 +87,6 @@
   [Range interface: existence and properties of interface prototype object]
     expected: FAIL
 
-  [Event interface: attribute returnValue]
-    expected: FAIL
-
-  [Event interface: document.createEvent("Event") must inherit property "returnValue" with the proper type]
-    expected: FAIL
-
-  [Event interface: new Event("foo") must inherit property "returnValue" with the proper type]
-    expected: FAIL
-
-  [Event interface: new CustomEvent("foo") must inherit property "returnValue" with the proper type]
-    expected: FAIL
 
 
 [interfaces.html?1-1000]
@@ -115,19 +104,6 @@
     expected: FAIL
 
 
-[interfaces.html?exclude=Node]
-  [Event interface: attribute returnValue]
-    expected: FAIL
-
-  [Event interface: document.createEvent("Event") must inherit property "returnValue" with the proper type]
-    expected: FAIL
-
-  [Event interface: new Event("foo") must inherit property "returnValue" with the proper type]
-    expected: FAIL
-
-  [Event interface: new CustomEvent("foo") must inherit property "returnValue" with the proper type]
-    expected: FAIL
-
   [Document interface: attribute origin]
     expected: FAIL
 
@@ -198,17 +174,6 @@
 [interfaces.html?include=Node]
 
 [interfaces.html?exclude=Node]
-  [Event interface: attribute returnValue]
-    expected: FAIL
-
-  [Event interface: document.createEvent("Event") must inherit property "returnValue" with the proper type]
-    expected: FAIL
-
-  [Event interface: new Event("foo") must inherit property "returnValue" with the proper type]
-    expected: FAIL
-
-  [Event interface: new CustomEvent("foo") must inherit property "returnValue" with the proper type]
-    expected: FAIL
 
   [Document interface: attribute origin]
     expected: FAIL
diff --git a/testing/web-platform/tests/css/css-filter/blur-clip-stacking-context-001.html b/testing/web-platform/tests/css/css-filter/blur-clip-stacking-context-001.html
new file mode 100644
index 000000000000..a96994a8afe1
--- /dev/null
+++ b/testing/web-platform/tests/css/css-filter/blur-clip-stacking-context-001.html
@@ -0,0 +1,35 @@
+<!doctype html>
+<title>CSS Test: Blurs are correctly clipped by an overflow: hidden ancestor</title>
+<link rel="author" href="mailto:emilio@crisal.io" title="Emilio Cobos Álvarez">
+<link rel="help" href="https://drafts.fxtf.org/filter-effects/#funcdef-filter-blur">
+<link rel="help" href="https://drafts.csswg.org/css-overflow-3/#valdef-overflow-hidden">
+<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1459065">
+<link rel="match" href="blur-clip-stacking-context-ref.html">
+<style>
+  #cover, #clip, #blur {
+    width: 100px;
+    height: 100px;
+  }
+
+  #cover, #clip {
+    position: absolute;
+    top: 10px;
+    left: 10px;
+  }
+
+  #cover {
+    background: green;
+  }
+
+  #clip {
+    overflow: hidden;
+    background: red;
+  }
+
+  #blur {
+    background: blue;
+    filter: blur(20px);
+  }
+</style>
+<div id="clip"><div id="blur"></div></div>
+<div id="cover"></div>
diff --git a/testing/web-platform/tests/css/css-filter/blur-clip-stacking-context-002.html b/testing/web-platform/tests/css/css-filter/blur-clip-stacking-context-002.html
new file mode 100644
index 000000000000..0473f1294944
--- /dev/null
+++ b/testing/web-platform/tests/css/css-filter/blur-clip-stacking-context-002.html
@@ -0,0 +1,28 @@
+<!doctype html>
+<title>CSS Test: Blurs on an overflow: hidden element are correctly not-clipped to the padding box</title>
+<link rel="author" href="mailto:emilio@crisal.io" title="Emilio Cobos Álvarez">
+<link rel="help" href="https://drafts.fxtf.org/filter-effects/#funcdef-filter-blur">
+<link rel="help" href="https://drafts.csswg.org/css-overflow-3/#valdef-overflow-hidden">
+<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1459065">
+<link rel="mismatch" href="blur-clip-stacking-context-ref.html">
+<style>
+  #cover, #clip {
+    position: absolute;
+    top: 10px;
+    left: 10px;
+    width: 100px;
+    height: 100px;
+  }
+
+  #cover {
+    background: green;
+  }
+
+  #clip {
+    overflow: hidden;
+    background: blue;
+    filter: blur(20px);
+  }
+</style>
+<div id="clip"></div>
+<div id="cover"></div>
diff --git a/testing/web-platform/tests/css/css-filter/blur-clip-stacking-context-ref.html b/testing/web-platform/tests/css/css-filter/blur-clip-stacking-context-ref.html
new file mode 100644
index 000000000000..82b907334fd7
--- /dev/null
+++ b/testing/web-platform/tests/css/css-filter/blur-clip-stacking-context-ref.html
@@ -0,0 +1,14 @@
+<!doctype html>
+<title>CSS Test Reference</title>
+<link rel="author" href="mailto:emilio@crisal.io" title="Emilio Cobos Álvarez">
+<style>
+  div {
+    position: absolute;
+    top: 10px;
+    left: 10px;
+    background: green;
+    width: 100px;
+    height: 100px;
+  }
+</style>
+<div></div>
diff --git a/toolkit/components/downloads/test/unit/head.js b/toolkit/components/downloads/test/unit/head.js
index f17840c8266d..74712596b6d0 100644
--- a/toolkit/components/downloads/test/unit/head.js
+++ b/toolkit/components/downloads/test/unit/head.js
@@ -589,7 +589,7 @@ function isValidDate(aDate) {
 function waitForAnnotation(sourceUriSpec, annotationName) {
   return TestUtils.waitForCondition(async () => {
     let pageInfo = await PlacesUtils.history.fetch(sourceUriSpec, {includeAnnotations: true});
-    return pageInfo.annotations.has(annotationName);
+    return pageInfo && pageInfo.annotations.has(annotationName);
   }, `Should have found annotation ${annotationName} for ${sourceUriSpec}`);
 }
 
diff --git a/toolkit/components/extensions/test/xpcshell/test_ext_contentscript_about_blank_start.js b/toolkit/components/extensions/test/xpcshell/test_ext_contentscript_about_blank_start.js
new file mode 100644
index 000000000000..ab9715869d67
--- /dev/null
+++ b/toolkit/components/extensions/test/xpcshell/test_ext_contentscript_about_blank_start.js
@@ -0,0 +1,69 @@
+"use strict";
+
+const server = createHttpServer({hosts: ["example.com"]});
+
+server.registerPathHandler("/blank-iframe.html", (request, response) => {
+  response.setStatusLine(request.httpVersion, 200, "OK");
+  response.setHeader("Content-Type", "text/html; charset=utf-8", false);
+  response.write("<iframe></iframe>");
+});
+
+add_task(async function content_script_at_document_start() {
+  let extensionData = {
+    manifest: {
+      content_scripts: [{
+        "matches": ["<all_urls>"],
+        "js": ["start.js"],
+        "run_at": "document_start",
+        "match_about_blank": true,
+      }],
+    },
+
+    files: {
+      "start.js": function() {
+        browser.test.sendMessage("content-script-done");
+      },
+    },
+  };
+
+  let extension = ExtensionTestUtils.loadExtension(extensionData);
+  await extension.startup();
+  let contentPage = await ExtensionTestUtils.loadContentPage(`about:blank`);
+  await extension.awaitMessage("content-script-done");
+  await contentPage.close();
+  await extension.unload();
+});
+
+add_task(async function content_style_at_document_start() {
+  let extensionData = {
+    manifest: {
+      content_scripts: [{
+        "matches": ["<all_urls>"],
+        "css": ["start.css"],
+        "run_at": "document_start",
+        "match_about_blank": true,
+      }, {
+        "matches": ["<all_urls>"],
+        "js": ["end.js"],
+        "run_at": "document_end",
+        "match_about_blank": true,
+      }],
+    },
+
+    files: {
+      "start.css": "body { background: red; }",
+      "end.js": function() {
+        let style = window.getComputedStyle(document.body);
+        browser.test.assertEq("rgb(255, 0, 0)", style.backgroundColor, "document_start style should have been applied");
+        browser.test.sendMessage("content-script-done");
+      },
+    },
+  };
+
+  let extension = ExtensionTestUtils.loadExtension(extensionData);
+  await extension.startup();
+  let contentPage = await ExtensionTestUtils.loadContentPage(`about:blank`);
+  await extension.awaitMessage("content-script-done");
+  await contentPage.close();
+  await extension.unload();
+});
diff --git a/toolkit/components/extensions/test/xpcshell/xpcshell-content.ini b/toolkit/components/extensions/test/xpcshell/xpcshell-content.ini
index 06c4edbf52a6..952442e3493c 100644
--- a/toolkit/components/extensions/test/xpcshell/xpcshell-content.ini
+++ b/toolkit/components/extensions/test/xpcshell/xpcshell-content.ini
@@ -2,8 +2,8 @@
 skip-if = os == "android" || (os == "win" && debug) || (os == "linux")
 [test_ext_i18n_css.js]
 [test_ext_contentscript.js]
+[test_ext_contentscript_about_blank_start.js]
 [test_ext_contentscript_scriptCreated.js]
-skip-if = debug # Bug 1407501
 [test_ext_contentscript_triggeringPrincipal.js]
 skip-if = (os == "android" && debug) || (os == "win" && debug) # Windows: Bug 1438796
 [test_ext_contentscript_xrays.js]
diff --git a/toolkit/components/passwordmgr/LoginManagerContent.jsm b/toolkit/components/passwordmgr/LoginManagerContent.jsm
index 43a708edcaed..6d0a80dfcdfb 100644
--- a/toolkit/components/passwordmgr/LoginManagerContent.jsm
+++ b/toolkit/components/passwordmgr/LoginManagerContent.jsm
@@ -436,14 +436,8 @@ var LoginManagerContent = {
   _fetchLoginsFromParentAndFillForm(form, window) {
     this._detectInsecureFormLikes(window);
 
-    const isPrivateWindow = PrivateBrowsingUtils.isContentWindowPrivate(window);
-
     let messageManager = window.docShell.messageManager;
-    messageManager.sendAsyncMessage("LoginStats:LoginEncountered",
-                                    {
-                                      isPrivateWindow,
-                                      isPwmgrEnabled: gEnabled,
-                                    });
+    messageManager.sendAsyncMessage("LoginStats:LoginEncountered");
 
     if (!gEnabled) {
       return;
diff --git a/toolkit/components/passwordmgr/LoginManagerParent.jsm b/toolkit/components/passwordmgr/LoginManagerParent.jsm
index be231cab01b7..1f7ad30eae0d 100644
--- a/toolkit/components/passwordmgr/LoginManagerParent.jsm
+++ b/toolkit/components/passwordmgr/LoginManagerParent.jsm
@@ -94,13 +94,6 @@ var LoginManagerParent = {
                           data.oldPasswordField,
                           msg.objects.openerTopWindow,
                           msg.target);
-
-        const flow_id = msg.target.ownerGlobal.gBrowser.getTabForBrowser(msg.target).linkedPanel;
-        Services.telemetry.recordEvent("savant", "login_form", "submit", null,
-                                      {
-                                        subcategory: "encounter",
-                                        flow_id,
-                                      });
         break;
       }
 
@@ -119,28 +112,6 @@ var LoginManagerParent = {
         AutoCompletePopup.removeLogin(login);
         break;
       }
-
-      case "LoginStats:LoginFillSuccessful": {
-        const flow_id = msg.target.ownerGlobal.gBrowser.getTabForBrowser(msg.target).linkedPanel;
-        Services.telemetry.recordEvent("savant", "pwmgr_use", "use", null,
-                                      {
-                                        subcategory: "feature",
-                                        flow_id,
-                                      });
-        break;
-      }
-
-      case "LoginStats:LoginEncountered": {
-        const canRecordSubmit = (!data.isPrivateWindow && data.isPwmgrEnabled).toString();
-        const flow_id = msg.target.ownerGlobal.gBrowser.getTabForBrowser(msg.target).linkedPanel;
-        Services.telemetry.recordEvent("savant", "login_form", "load", null,
-                                      {
-                                        subcategory: "encounter",
-                                        flow_id,
-                                        canRecordSubmit,
-                                      });
-        break;
-      }
     }
 
     return undefined;
diff --git a/toolkit/components/passwordmgr/nsLoginManagerPrompter.js b/toolkit/components/passwordmgr/nsLoginManagerPrompter.js
index d3b14934f430..d19046e7c9a3 100644
--- a/toolkit/components/passwordmgr/nsLoginManagerPrompter.js
+++ b/toolkit/components/passwordmgr/nsLoginManagerPrompter.js
@@ -823,14 +823,6 @@ LoginManagerPrompter.prototype = {
     histogram.add(PROMPT_DISPLAYED);
     Services.obs.notifyObservers(null, "weave:telemetry:histogram", histogramName);
 
-    const promptType = type == "password-save" ? "save" : "update";
-    const flow_id = browser.ownerGlobal.gBrowser.getTabForBrowser(browser).linkedPanel;
-    Services.telemetry.recordEvent("savant", "pwmgr", "ask", promptType,
-                                  {
-                                    subcategory: "prompt",
-                                    flow_id,
-                                  });
-
     let chromeDoc = browser.ownerDocument;
 
     let currentNotification;
@@ -958,20 +950,8 @@ LoginManagerPrompter.prototype = {
       accessKey: this._getLocalizedString(initialMsgNames.buttonAccessKey),
       callback: () => {
         histogram.add(PROMPT_ADD_OR_UPDATE);
-        const flow_id = browser.ownerGlobal.gBrowser.getTabForBrowser(browser).linkedPanel;
         if (histogramName == "PWMGR_PROMPT_REMEMBER_ACTION") {
           Services.obs.notifyObservers(null, "LoginStats:NewSavedPassword");
-          Services.telemetry.recordEvent("savant", "pwmgr", "save", null,
-                                        {
-                                          subcategory: "prompt",
-                                          flow_id,
-                                        });
-        } else if (histogramName == "PWMGR_PROMPT_UPDATE_ACTION") {
-          Services.telemetry.recordEvent("savant", "pwmgr", "update", null,
-                                        {
-                                          subcategory: "prompt",
-                                          flow_id,
-                                        });
         }
         readDataFromUI();
         persistData();
diff --git a/toolkit/components/reader/ReaderMode.jsm b/toolkit/components/reader/ReaderMode.jsm
index b8cce759bc74..a81e031e9c17 100644
--- a/toolkit/components/reader/ReaderMode.jsm
+++ b/toolkit/components/reader/ReaderMode.jsm
@@ -98,9 +98,6 @@ var ReaderMode = {
    * if not, append the about:reader page in the history instead.
    */
   enterReaderMode(docShell, win) {
-    Services.telemetry.recordEvent("savant", "readermode", "on", null,
-                                  { subcategory: "feature" });
-
     let url = win.document.location.href;
     let readerURL = "about:reader?url=" + encodeURIComponent(url);
     let webNav = docShell.QueryInterface(Ci.nsIWebNavigation);
@@ -122,8 +119,6 @@ var ReaderMode = {
    * if not, append the original page in the history instead.
    */
   leaveReaderMode(docShell, win) {
-    Services.telemetry.recordEvent("savant", "readermode", "off", null,
-                                  { subcategory: "feature" });
     let url = win.document.location.href;
     let originalURL = this.getOriginalUrl(url);
     let webNav = docShell.QueryInterface(Ci.nsIWebNavigation);
diff --git a/toolkit/components/telemetry/Events.yaml b/toolkit/components/telemetry/Events.yaml
index b85499fa5967..1aaf6146e3b8 100644
--- a/toolkit/components/telemetry/Events.yaml
+++ b/toolkit/components/telemetry/Events.yaml
@@ -113,206 +113,6 @@ navigation:
     extra_keys:
       engine: The id of the search engine used.
 
-# This category contains event entries used for the Savant Shield study.
-savant:
-  # Mostly a dupe of "search" event from "navigation" category to ensure only Savant
-  # code enables/disables it.
-  search:
-    objects: ["about_home", "about_newtab", "contextmenu", "oneoff",
-              "suggestion", "alias", "enter", "searchbar", "urlbar"]
-    release_channel_collection: opt-out
-    record_in_processes: ["main"]
-    description: >
-      This is recorded on each search navigation.
-      The value field records the action used to trigger the search:
-        "enter", "oneoff", "suggestion", "alias", null (for contextmenu)
-    bug_numbers: [1316281, 1457226, 1462725]
-    notification_emails:
-      - "bdanforth@mozilla.com"
-      - "shong@mozilla.com"
-    expiry_version: "65"
-    extra_keys:
-      subcategory: The broad event category for this probe. E.g. navigation
-      engine: The id of the search engine used.
-  end_study:
-    objects: ["ineligible", "study_disable", "expired"]
-    release_channel_collection: opt-out
-    record_in_processes: ["main"]
-    description: >
-      This is recorded any time a study ending condition occurs for the Savant
-      Shield study. The object field records the reason that caused the ending.
-    bug_numbers: [1457226, 1462725]
-    notification_emails:
-      - "bdanforth@mozilla.com"
-      - "shong@mozilla.com"
-    expiry_version: "65"
-    extra_keys:
-      subcategory: The broad event category for this probe. E.g. navigation
-  readermode:
-    objects: ["on", "off"]
-    release_channel_collection: opt-out
-    record_in_processes: ["content"]
-    description: >
-      This is recorded any time Reader Mode is turned on or off.
-    bug_numbers: [1457226, 1465698]
-    notification_emails:
-      - "bdanforth@mozilla.com"
-      - "shong@mozilla.com"
-    expiry_version: "65"
-    extra_keys:
-      subcategory: The broad event category for this probe. E.g. navigation
-  addon:
-    objects: ["install_start", "install_finish", "remove_start", "remove_finish",
-              "enable", "disable" ]
-    release_channel_collection: opt-out
-    record_in_processes: ["main"]
-    description: >
-      This is recorded any time an addon event as listed in the objects field fires.
-      The value field records the addon ID for the event.
-    bug_numbers: [1457226, 1465707]
-    notification_emails:
-      - "bdanforth@mozilla.com"
-      - "shong@mozilla.com"
-    expiry_version: "65"
-    extra_keys:
-      subcategory: The broad event category for this probe. E.g. navigation
-  bookmark:
-    objects: ["save", "remove"]
-    release_channel_collection: opt-out
-    record_in_processes: ["main"]
-    description: >
-      This is recorded any time a bookmark is saved or removed.
-    bug_numbers: [1457226, 1465703]
-    notification_emails:
-      - "bdanforth@mozilla.com"
-      - "shong@mozilla.com"
-    expiry_version: "65"
-    extra_keys:
-      subcategory: The broad event category for this probe. E.g. navigation
-  follow_bookmark:
-    objects: ["open"]
-    release_channel_collection: opt-out
-    record_in_processes: ["main"]
-    description: >
-      This is recorded any time a bookmark is visited.
-    bug_numbers: [1457226, 1465703]
-    notification_emails:
-      - "bdanforth@mozilla.com"
-      - "shong@mozilla.com"
-    expiry_version: "65"
-    extra_keys:
-      subcategory: The broad event category for this probe. E.g. navigation
-  follow_urlbar_link:
-    objects: ["bookmark", "history"]
-    release_channel_collection: opt-out
-    record_in_processes: ["main"]
-    description: >
-      This is recorded when the user selects a urlbar bookmark or history result.
-    bug_numbers: [1457226, 1465704]
-    notification_emails:
-      - "bdanforth@mozilla.com"
-      - "shong@mozilla.com"
-    expiry_version: "65"
-    extra_keys:
-      subcategory: The broad event category for this probe. E.g. navigation
-  library_menu:
-    objects: ["open"]
-    release_channel_collection: opt-out
-    record_in_processes: ["main"]
-    description: >
-      This is recorded any time the library menu is opened.
-    bug_numbers: [1457226, 1465697]
-    notification_emails:
-      - "bdanforth@mozilla.com"
-      - "shong@mozilla.com"
-    expiry_version: "65"
-    extra_keys:
-      subcategory: The broad event category for this probe. E.g. navigation
-  hamburger_menu:
-    objects: ["open"]
-    release_channel_collection: opt-out
-    record_in_processes: ["main"]
-    description: >
-      This is recorded any time the hamburger menu is opened.
-    bug_numbers: [1457226, 1465697]
-    notification_emails:
-      - "bdanforth@mozilla.com"
-      - "shong@mozilla.com"
-    expiry_version: "65"
-    extra_keys:
-      subcategory: The broad event category for this probe. E.g. navigation
-  dotdotdot_menu:
-    objects: ["open"]
-    release_channel_collection: opt-out
-    record_in_processes: ["main"]
-    description: >
-      This is recorded any time the dotdotdot (aka pageAction) menu is opened.
-    bug_numbers: [1457226, 1465697]
-    notification_emails:
-      - "bdanforth@mozilla.com"
-      - "shong@mozilla.com"
-    expiry_version: "65"
-    extra_keys:
-      subcategory: The broad event category for this probe. E.g. navigation
-  pwmgr_use:
-    objects: ["use"]
-    release_channel_collection: opt-out
-    record_in_processes: ["main"]
-    description: >
-      Client uses saved login information from the Password Manager
-    bug_numbers: [1457226, 1465685]
-    notification_emails:
-      - "bdanforth@mozilla.com"
-      - "shong@mozilla.com"
-    expiry_version: "65"
-    extra_keys:
-      subcategory: The broad event category for this probe. E.g. navigation
-      flow_id: A tab identifier to associate events occuring in the same tab
-  pwmgr:
-    objects: ["ask", "save", "update"]
-    release_channel_collection: opt-out
-    record_in_processes: ["main"]
-    description: >
-      Password Manager asks the user to save or update login information.
-      For ask prompts, the value field indicate a save versus update ask.
-    bug_numbers: [1457226, 1465685]
-    notification_emails:
-      - "bdanforth@mozilla.com"
-      - "shong@mozilla.com"
-    expiry_version: "65"
-    extra_keys:
-      subcategory: The broad event category for this probe. E.g. navigation
-      flow_id: A tab identifier to associate events occuring in the same tab
-  login_form:
-    objects: ["load", "submit"]
-    release_channel_collection: opt-out
-    record_in_processes: ["main"]
-    description: >
-      A login form has been loaded or submitted. Login form submit events only
-      fire in non-private windows with Password Manager enabled.
-    bug_numbers: [1457226, 1465685]
-    notification_emails:
-      - "bdanforth@mozilla.com"
-      - "shong@mozilla.com"
-    expiry_version: "65"
-    extra_keys:
-      subcategory: The broad event category for this probe. E.g. navigation
-      flow_id: A tab identifier to associate events occuring in the same tab
-      canRecordSubmit: True if a login form loads in a non-private window with Password Manager enabled.
-  tab:
-    objects: ["open", "close", "select"]
-    release_channel_collection: opt-out
-    record_in_processes: ["main"]
-    description: >
-      This is recorded any time a tab is opened, closed or selected.
-    bug_numbers: [1457226, 1465694]
-    notification_emails:
-      - "bdanforth@mozilla.com"
-      - "shong@mozilla.com"
-    expiry_version: "65"
-    extra_keys:
-      subcategory: The broad event category for this probe. E.g. navigation
-
 # This category contains event entries used for Telemetry tests.
 # They will not be sent out with any pings.
 telemetry.test:
diff --git a/toolkit/components/telemetry/Histograms.json b/toolkit/components/telemetry/Histograms.json
index 0faea38e5553..5e8207a1b89a 100644
--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -1100,7 +1100,7 @@
     "high": 1024,
     "n_buckets": 21,
     "description": "Number of low-virtual-memory events fired since last ping",
-    "cpp_guard": "XP_WIN",
+    "operating_systems": ["windows"],
     "bug_numbers": [711490,1451005]
   },
   "LOW_MEMORY_EVENTS_PHYSICAL": {
@@ -1111,7 +1111,7 @@
     "high": 1024,
     "n_buckets": 21,
     "description": "Number of low-physical-memory events fired since last ping",
-    "cpp_guard": "XP_WIN",
+    "operating_systems": ["windows"],
     "bug_numbers": [711490,1451005]
   },
   "LOW_MEMORY_EVENTS_COMMIT_SPACE": {
@@ -1122,7 +1122,7 @@
     "high": 1024,
     "n_buckets": 21,
     "description": "Number of low-commit-space events fired since last ping",
-    "cpp_guard": "XP_WIN",
+    "operating_systems": ["windows"],
     "bug_numbers": [1451005]
   },
   "PAGE_FAULTS_HARD": {
@@ -1133,7 +1133,7 @@
     "high": 65536,
     "n_buckets": 13,
     "description": "Hard page faults (since last telemetry ping)",
-    "cpp_guard": "XP_UNIX"
+    "operating_systems": ["unix"]
   },
   "FONTLIST_INITOTHERFAMILYNAMES": {
     "record_in_processes": ["main", "content"],
@@ -1166,7 +1166,7 @@
     "high": 30000,
     "n_buckets": 10,
     "description": "gfxDWriteFontList::DelayedInitFontList Total (ms)",
-    "cpp_guard": "XP_WIN"
+    "operating_systems": ["windows"]
   },
   "DWRITEFONT_DELAYEDINITFONTLIST_COUNT": {
     "record_in_processes": ["main", "content"],
@@ -1175,7 +1175,7 @@
     "high": 10000,
     "n_buckets": 10,
     "description": "gfxDWriteFontList::DelayedInitFontList Font Family Count",
-    "cpp_guard": "XP_WIN"
+    "operating_systems": ["windows"]
   },
   "DWRITEFONT_DELAYEDINITFONTLIST_COLLECT": {
     "record_in_processes": ["main", "content"],
@@ -1184,7 +1184,7 @@
     "high": 30000,
     "n_buckets": 10,
     "description": "gfxDWriteFontList::DelayedInitFontList GetSystemFontCollection (ms)",
-    "cpp_guard": "XP_WIN"
+    "operating_systems": ["windows"]
   },
   "DWRITEFONT_INIT_PROBLEM": {
     "record_in_processes": ["main", "content"],
@@ -1192,7 +1192,7 @@
     "kind": "enumerated",
     "n_values": 8,
     "description": "DirectWrite system fontlist initialization problem (1=GDI interop, 2=system font collection, 3=no fonts)",
-    "cpp_guard": "XP_WIN"
+    "operating_systems": ["windows"]
   },
   "GDI_INITFONTLIST_TOTAL": {
     "record_in_processes": ["main", "content"],
@@ -1201,7 +1201,7 @@
     "high": 30000,
     "n_buckets": 10,
     "description": "gfxGDIFontList::InitFontList Total (ms)",
-    "cpp_guard": "XP_WIN"
+    "operating_systems": ["windows"]
   },
   "MAC_INITFONTLIST_TOTAL": {
     "record_in_processes": ["main", "content"],
@@ -1210,7 +1210,7 @@
     "high": 30000,
     "n_buckets": 10,
     "description": "gfxMacPlatformFontList::InitFontList Total (ms)",
-    "cpp_guard": "XP_DARWIN"
+    "operating_systems": ["mac"]
   },
   "SYSTEM_FONT_FALLBACK": {
     "record_in_processes": ["main", "content"],
@@ -5033,7 +5033,7 @@
     "expires_in_version": "never",
     "kind": "flag",
     "description": "Whether the referrer intent specified an invalid distribution name",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_DISTRIBUTION_CODE_CATEGORY": {
     "record_in_processes": ["main", "content"],
@@ -5041,7 +5041,7 @@
     "kind": "enumerated",
     "n_values": 20,
     "description": "First digit of HTTP result code, or error category, during distribution download",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_DISTRIBUTION_DOWNLOAD_TIME_MS": {
     "record_in_processes": ["main", "content"],
@@ -5051,7 +5051,7 @@
     "high": 40000,
     "n_buckets": 30,
     "description": "Time taken to download a specified distribution file (msec)",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_BOOKMARKS_COUNT": {
     "record_in_processes": ["main", "content"],
@@ -5067,7 +5067,7 @@
     "record_in_processes": ["main", "content"],
     "expires_in_version": "70",
     "kind": "flag",
-    "cpp_guard": "ANDROID",
+    "operating_systems": ["android"],
     "description": "Whether or not users have Orbot installed",
     "alert_emails": ["seceng@mozilla.org"],
     "bug_numbers": [1314784]
@@ -5078,7 +5078,7 @@
     "kind": "exponential",
     "high": 1000,
     "n_buckets": 10,
-    "cpp_guard": "ANDROID",
+    "operating_systems": ["android"],
     "description": "Number of reading list items stored in the browser DB *** No longer needed (bug 1156565). Delete histogram and accumulation code! ***"
   },
   "FENNEC_READER_VIEW_CACHE_SIZE": {
@@ -5102,7 +5102,7 @@
     "n_buckets": 22,
     "description": "Latency in microseconds of UI events in the Android event loop between posting and processing",
     "bug_numbers": [1322574],
-    "cpp_guard": "MOZ_WIDGET_ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_LOOP_OTHER_LATENCY": {
     "record_in_processes": ["main", "content"],
@@ -5114,7 +5114,7 @@
     "n_buckets": 22,
     "description": "Latency in microseconds of non-UI events in the Android event loop between posting and processing",
     "bug_numbers": [1322574],
-    "cpp_guard": "MOZ_WIDGET_ANDROID"
+    "operating_systems": ["android"]
   },
   "PLACES_SORTED_BOOKMARKS_PERC": {
     "record_in_processes": ["main", "content"],
@@ -7626,6 +7626,54 @@
     "description": "a testing histogram; not meant to be touched",
     "products": ["fennec", "geckoview"]
   },
+  "TELEMETRY_TEST_OS_ANDROID_ONLY": {
+    "record_in_processes": ["all"],
+    "alert_emails": ["telemetry-client-dev@mozilla.com"],
+    "expires_in_version": "never",
+    "kind": "linear",
+    "low": 1,
+    "high": 10000,
+    "n_buckets": 10,
+    "bug_numbers": [1477213],
+    "description": "a testing histogram; not meant to be touched",
+    "operating_systems": ["android"]
+  },
+  "TELEMETRY_TEST_OS_WIN_ONLY": {
+    "record_in_processes": ["all"],
+    "alert_emails": ["telemetry-client-dev@mozilla.com"],
+    "expires_in_version": "never",
+    "kind": "linear",
+    "low": 1,
+    "high": 10000,
+    "n_buckets": 10,
+    "bug_numbers": [1477213],
+    "description": "a testing histogram; not meant to be touched",
+    "operating_systems": ["windows"]
+  },
+  "TELEMETRY_TEST_OS_LINUX_ONLY": {
+    "record_in_processes": ["all"],
+    "alert_emails": ["telemetry-client-dev@mozilla.com"],
+    "expires_in_version": "never",
+    "kind": "linear",
+    "low": 1,
+    "high": 10000,
+    "n_buckets": 10,
+    "bug_numbers": [1477213],
+    "description": "a testing histogram; not meant to be touched",
+    "operating_systems": ["linux"]
+  },
+  "TELEMETRY_TEST_OS_MAC_ONLY": {
+    "record_in_processes": ["all"],
+    "alert_emails": ["telemetry-client-dev@mozilla.com"],
+    "expires_in_version": "never",
+    "kind": "linear",
+    "low": 1,
+    "high": 10000,
+    "n_buckets": 10,
+    "bug_numbers": [1477213],
+    "description": "a testing histogram; not meant to be touched",
+    "operating_systems": ["mac"]
+  },
   "STARTUP_CRASH_DETECTED": {
     "record_in_processes": ["main", "content"],
     "expires_in_version": "never",
@@ -7682,7 +7730,7 @@
     "high": 50000,
     "n_buckets": 20,
     "description": "Number of bookmarks in the original XUL places database",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_GLOBALHISTORY_ADD_MS": {
     "record_in_processes": ["main", "content"],
@@ -7692,7 +7740,7 @@
     "high": 20000,
     "n_buckets": 20,
     "description": "Time for a record to be added to history (ms)",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_GLOBALHISTORY_UPDATE_MS": {
     "record_in_processes": ["main", "content"],
@@ -7702,7 +7750,7 @@
     "high": 20000,
     "n_buckets": 20,
     "description": "Time for a record to be updated in history (ms)",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_GLOBALHISTORY_VISITED_BUILD_MS": {
     "record_in_processes": ["main", "content"],
@@ -7712,14 +7760,14 @@
     "high": 20000,
     "n_buckets": 20,
     "description": "Time to update the visited link set (ms)",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_RESTORING_ACTIVITY": {
     "record_in_processes": ["main", "content"],
     "expires_in_version": "never",
     "kind": "flag",
     "description": "Fennec is starting up but the Gecko thread was still running",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_SEARCH_LOADER_TIME_MS": {
     "record_in_processes": ["main", "content"],
@@ -7729,7 +7777,7 @@
     "high": 20000,
     "n_buckets": 20,
     "description": "Time for a URL bar DB search to return (ms)",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_STARTUP_TIME_GECKOREADY": {
     "record_in_processes": ["main", "content"],
@@ -7739,7 +7787,7 @@
     "high": 20000,
     "n_buckets": 20,
     "description": "Time for the Gecko:Ready message to arrive (ms)",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_STARTUP_TIME_JAVAUI": {
     "record_in_processes": ["main", "content"],
@@ -7749,7 +7797,7 @@
     "high": 5000,
     "n_buckets": 20,
     "description": "Time for the Java UI to load (ms)",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_TOPSITES_LOADER_TIME_MS": {
     "record_in_processes": ["main", "content"],
@@ -7759,7 +7807,7 @@
     "high": 20000,
     "n_buckets": 20,
     "description": "Time for the home screen Top Sites query to return with no filter set (ms)",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_ACTIVITY_STREAM_TOPSITES_LOADER_TIME_MS": {
     "record_in_processes": ["main", "content"],
@@ -7771,7 +7819,7 @@
     "description": "Time for the Activity Stream home screen Top Sites query to return (ms)",
     "alert_emails": ["mobile-frontend@mozilla.com"],
     "bug_numbers": [1293790],
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_ACTIVITY_STREAM_HIGHLIGHTS_LOADER_TIME_MS": {
     "record_in_processes": ["main", "content"],
@@ -7783,7 +7831,7 @@
     "description": "Time for the Activity Stream highlights query to return (ms)",
     "alert_emails": ["mobile-frontend@mozilla.com"],
     "bug_numbers": [1298786],
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_HOMEPANELS_CUSTOM": {
     "record_in_processes": ["main", "content"],
@@ -7791,14 +7839,14 @@
     "kind": "boolean",
     "bug_numbers": [1245368],
     "description": "Whether the user has customized their homepanels",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_WAS_KILLED": {
     "record_in_processes": ["main", "content"],
     "expires_in_version": "never",
     "kind": "flag",
     "description": "Killed, likely due to an OOM condition",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FIPS_ENABLED": {
     "record_in_processes": ["main", "content"],
@@ -7987,7 +8035,7 @@
     "bug_numbers": [795307, 1390269],
     "alert_emails": ["jimm@mozilla.com"],
     "description": "Boolean indicating if a touch input device is detected.",
-    "cpp_guard": "XP_WIN"
+    "operating_systems": ["windows"]
   },
   "COMPONENTS_SHIM_ACCESSED_BY_CONTENT": {
     "record_in_processes": ["main", "content"],
@@ -12579,7 +12627,7 @@
     "bug_numbers": [1098428],
     "expires_in_version": "55",
     "kind": "boolean",
-    "cpp_guard": "XP_LINUX",
+    "operating_systems": ["linux"],
     "description": "Whether the system has seccomp-bpf capability"
   },
   "SANDBOX_HAS_SECCOMP_TSYNC": {
@@ -12588,7 +12636,7 @@
     "bug_numbers": [1098428, 1370578],
     "expires_in_version": "61",
     "kind": "boolean",
-    "cpp_guard": "XP_LINUX",
+    "operating_systems": ["linux"],
     "description": "Whether the system has seccomp-bpf thread-sync capability"
   },
   "SANDBOX_HAS_USER_NAMESPACES": {
@@ -12598,7 +12646,7 @@
     "expires_in_version": "65",
     "releaseChannelCollection": "opt-out",
     "kind": "boolean",
-    "cpp_guard": "XP_LINUX",
+    "operating_systems": ["linux"],
     "description": "Whether our process succedeed in creating a user namespace"
   },
   "SANDBOX_HAS_USER_NAMESPACES_PRIVILEGED": {
@@ -12607,7 +12655,7 @@
     "bug_numbers": [1098428, 1370578],
     "expires_in_version": "61",
     "kind": "boolean",
-    "cpp_guard": "XP_LINUX",
+    "operating_systems": ["linux"],
     "description": "Whether the system has the capability to create privileged user namespaces"
   },
  "SANDBOX_MEDIA_ENABLED": {
@@ -12616,7 +12664,7 @@
     "bug_numbers": [1098428],
     "expires_in_version": "55",
     "kind": "boolean",
-    "cpp_guard": "XP_LINUX",
+    "operating_systems": ["linux"],
     "description": "Whether the sandbox is enabled for media/GMP plugins"
   },
  "SANDBOX_CONTENT_ENABLED": {
@@ -12625,7 +12673,7 @@
     "bug_numbers": [1098428],
     "expires_in_version": "55",
     "kind": "boolean",
-    "cpp_guard": "XP_LINUX",
+    "operating_systems": ["linux"],
     "description": "Whether the sandbox is enabled for the content process"
   },
   "SANDBOX_REJECTED_SYSCALLS": {
@@ -12636,7 +12684,7 @@
     "releaseChannelCollection": "opt-out",
     "kind": "count",
     "keyed": true,
-    "cpp_guard": "XP_LINUX",
+    "operating_systems": ["linux"],
     "description": "System calls blocked by a seccomp-bpf sandbox policy; limited to syscalls where we would crash on Nightly.  The key is generally the architecture and syscall ID but in some cases we include non-personally-identifying information from the syscall arguments; see the function SubmitToTelemetry in security/sandbox/linux/reporter/SandboxReporter.cpp for details."
   },
   "SANDBOX_FAILED_LAUNCH_KEYED": {
@@ -12647,7 +12695,7 @@
     "keyed": true,
     "n_values": 50,
     "bug_numbers": [1368600],
-    "cpp_guard": "XP_WIN",
+    "operating_systems": ["windows"],
     "description": "Error code when a Windows sandboxed process fails to launch, keyed by process type and Windows error code. See https://dxr.mozilla.org/mozilla-central/search?q=ResultCode++path%3Asandbox_types.h&redirect=true for definitions of the error codes."
   },
   "SYNC_WORKER_OPERATION": {
@@ -12819,7 +12867,7 @@
     "kind": "flag",
     "bug_numbers": [1284017],
     "description": "When restoring tabs on startup, reading from sessionstore.js failed, even though the file exists and is not containing an explicitly empty window.",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_SESSIONSTORE_RESTORING_FROM_BACKUP": {
     "record_in_processes": ["main", "content"],
@@ -12828,7 +12876,7 @@
     "kind": "flag",
     "bug_numbers": [1190627],
     "description": "When restoring tabs on startup, reading from sessionstore.js failed, but sessionstore.bak was read successfully.",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "FENNEC_SESSIONSTORE_ALL_FILES_DAMAGED": {
     "record_in_processes": ["main", "content"],
@@ -12837,7 +12885,7 @@
     "kind": "flag",
     "bug_numbers": [1337115],
     "description": "Both the main session file and its backup could not be read and and the first run pref is false.",
-    "cpp_guard": "ANDROID"
+    "operating_systems": ["android"]
   },
   "NUMBER_OF_PROFILES": {
     "record_in_processes": ["main", "content"],
diff --git a/toolkit/components/telemetry/Scalars.yaml b/toolkit/components/telemetry/Scalars.yaml
index 1ef7817908c6..cf1aa0540f98 100644
--- a/toolkit/components/telemetry/Scalars.yaml
+++ b/toolkit/components/telemetry/Scalars.yaml
@@ -1564,21 +1564,6 @@ telemetry:
     record_in_processes:
       - 'main'
 
-  os_shutting_down:
-    bug_numbers:
-      - 1480826
-    description: >
-      Records true if there is a signal that Firefox was quitting because
-      the OS was shutting down. Only available on Windows.
-    expires: "64"
-    kind: boolean
-    notification_emails:
-      - telemetry-client-dev@mozilla.com
-      - agashlin@mozilla.com
-    release_channel_collection: opt-out
-    record_in_processes:
-      - 'main'
-
 telemetry.discarded:
   accumulations:
     bug_numbers:
diff --git a/toolkit/components/telemetry/Telemetry.cpp b/toolkit/components/telemetry/Telemetry.cpp
index d9283c8b00a2..4f2a2a620495 100644
--- a/toolkit/components/telemetry/Telemetry.cpp
+++ b/toolkit/components/telemetry/Telemetry.cpp
@@ -227,10 +227,6 @@ TelemetryImpl::CollectReports(nsIHandleReportCallback* aHandleReport,
   COLLECT_REPORT("explicit/telemetry/impl", aMallocSizeOf(this),
       "Memory used by the Telemetry core implemenation");
 
-  COLLECT_REPORT("explicit/telemetry/histogram/shallow",
-      TelemetryHistogram::GetMapShallowSizesOfExcludingThis(aMallocSizeOf),
-      "Memory used by the Telemetry Histogram implementation");
-
   COLLECT_REPORT("explicit/telemetry/scalar/shallow",
       TelemetryScalar::GetMapShallowSizesOfExcludingThis(aMallocSizeOf),
       "Memory used by the Telemetry Scalar implemenation");
diff --git a/toolkit/components/telemetry/TelemetryHistogram.cpp b/toolkit/components/telemetry/TelemetryHistogram.cpp
index a23ce2ff5ca9..49180f87d9a9 100644
--- a/toolkit/components/telemetry/TelemetryHistogram.cpp
+++ b/toolkit/components/telemetry/TelemetryHistogram.cpp
@@ -25,6 +25,7 @@
 
 #include "TelemetryCommon.h"
 #include "TelemetryHistogram.h"
+#include "TelemetryHistogramNameMap.h"
 #include "TelemetryScalar.h"
 #include "ipc/TelemetryIPCAccumulator.h"
 
@@ -45,6 +46,7 @@ using mozilla::Telemetry::KeyedHistogramAccumulation;
 using mozilla::Telemetry::HistogramID;
 using mozilla::Telemetry::ProcessID;
 using mozilla::Telemetry::HistogramCount;
+using mozilla::Telemetry::HistogramIDByNameLookup;
 using mozilla::Telemetry::Common::LogToBrowserConsole;
 using mozilla::Telemetry::Common::RecordedProcessType;
 using mozilla::Telemetry::Common::AutoHashtable;
@@ -236,9 +238,6 @@ Histogram** gHistogramStorage;
 // Keyed histograms internally map string keys to individual Histogram instances.
 KeyedHistogram** gKeyedHistogramStorage;
 
-// Cache of histogram name to a histogram id.
-StringToHistogramIdMap gNameToHistogramIDMap(HistogramCount);
-
 // To simplify logic below we use a single histogram instance for all expired histograms.
 Histogram* gExpiredHistogram = nullptr;
 
@@ -254,7 +253,6 @@ bool gHistogramRecordingDisabled[HistogramCount] = {};
 
 } // namespace
 
-
 ////////////////////////////////////////////////////////////////////////
 ////////////////////////////////////////////////////////////////////////
 //
@@ -418,12 +416,18 @@ internal_GetHistogramIdByName(const StaticMutexAutoLock& aLock,
                               const nsACString& name,
                               HistogramID* id)
 {
-  const bool found = gNameToHistogramIDMap.Get(name, id);
-  if (!found) {
-    return NS_ERROR_ILLEGAL_VALUE;
+  const uint32_t idx = HistogramIDByNameLookup(name);
+  MOZ_ASSERT(idx < HistogramCount, "Intermediate lookup should always give a valid index.");
+
+  // The lookup hashes the input and uses it as an index into the value array.
+  // Hash collisions can still happen for unknown values,
+  // therefore we check that the name matches.
+  if (name.Equals(gHistogramInfos[idx].name())) {
+    *id = HistogramID(idx);
+    return NS_OK;
   }
 
-  return NS_OK;
+  return NS_ERROR_ILLEGAL_VALUE;
 }
 
 // Clear a histogram from storage.
@@ -1994,29 +1998,6 @@ void TelemetryHistogram::InitializeGlobalState(bool canRecordBase,
       new KeyedHistogram*[HistogramCount * size_t(ProcessID::Count)] {};
   }
 
-  // gNameToHistogramIDMap should have been pre-sized correctly at the
-  // declaration point further up in this file.
-
-  // Populate the static histogram name->id cache.
-  // Note that the histogram names come from a static table so we can wrap them
-  // in a literal string to avoid allocations when it gets copied.
-  for (uint32_t i = 0; i < HistogramCount; i++) {
-    auto name = gHistogramInfos[i].name();
-
-    // Make sure the name pointer is in a valid region. See bug 1428612.
-    MOZ_DIAGNOSTIC_ASSERT(name >= gHistogramStringTable);
-    MOZ_DIAGNOSTIC_ASSERT(
-        uintptr_t(name) < (uintptr_t(gHistogramStringTable) + sizeof(gHistogramStringTable)));
-
-    nsCString wrappedName;
-    wrappedName.AssignLiteral(name, strlen(name));
-    gNameToHistogramIDMap.Put(wrappedName, HistogramID(i));
-  }
-
-#ifdef DEBUG
-  gNameToHistogramIDMap.MarkImmutable();
-#endif
-
     // Some Telemetry histograms depend on the value of C++ constants and hardcode
     // their values in Histograms.json.
     // We add static asserts here for those values to match so that future changes
@@ -2046,7 +2027,6 @@ void TelemetryHistogram::DeInitializeGlobalState()
   StaticMutexAutoLock locker(gTelemetryHistogramMutex);
   gCanRecordBase = false;
   gCanRecordExtended = false;
-  gNameToHistogramIDMap.Clear();
   gInitDone = false;
 
   // FactoryGet `new`s Histograms for us, but requires us to manually delete.
@@ -2577,14 +2557,6 @@ TelemetryHistogram::GetKeyedHistogramSnapshots(JSContext* aCx,
   return NS_OK;
 }
 
-size_t
-TelemetryHistogram::GetMapShallowSizesOfExcludingThis(mozilla::MallocSizeOf
-                                                      aMallocSizeOf)
-{
-  StaticMutexAutoLock locker(gTelemetryHistogramMutex);
-  return gNameToHistogramIDMap.ShallowSizeOfExcludingThis(aMallocSizeOf);
-}
-
 size_t
 TelemetryHistogram::GetHistogramSizesOfIncludingThis(mozilla::MallocSizeOf
                                                      aMallocSizeOf)
diff --git a/toolkit/components/telemetry/TelemetryHistogram.h b/toolkit/components/telemetry/TelemetryHistogram.h
index 7df5da747b0f..b9ffafaa6b4f 100644
--- a/toolkit/components/telemetry/TelemetryHistogram.h
+++ b/toolkit/components/telemetry/TelemetryHistogram.h
@@ -76,9 +76,6 @@ nsresult
 GetKeyedHistogramSnapshots(JSContext *aCx, JS::MutableHandleValue aResult, unsigned int aDataset,
                            bool aClearSubsession);
 
-size_t
-GetMapShallowSizesOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf);
-
 size_t
 GetHistogramSizesOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf);
 
diff --git a/toolkit/components/telemetry/TelemetrySend.jsm b/toolkit/components/telemetry/TelemetrySend.jsm
index da748002641a..dfa392035b11 100644
--- a/toolkit/components/telemetry/TelemetrySend.jsm
+++ b/toolkit/components/telemetry/TelemetrySend.jsm
@@ -800,7 +800,6 @@ var TelemetrySendImpl = {
     let setOSShutdown = () => {
       this._log.trace("setOSShutdown - in OS shutdown");
       this._isOSShutdown = true;
-      Telemetry.scalarSet("telemetry.os_shutting_down", true);
     };
 
     switch (topic) {
diff --git a/toolkit/components/telemetry/docs/collection/histograms.rst b/toolkit/components/telemetry/docs/collection/histograms.rst
index ef91621676d7..8fb81a3d39c9 100644
--- a/toolkit/components/telemetry/docs/collection/histograms.rst
+++ b/toolkit/components/telemetry/docs/collection/histograms.rst
@@ -184,10 +184,24 @@ Required for all new histograms. This is an array of integers and should at leas
 ---------------
 Required. A description of the data tracked by the histogram, e.g. _"Resident memory size"_
 
-``cpp_guard``
--------------
+``cpp_guard`` (obsolete, use ``operating_systems``)
+---------------------------------------------------
 Optional. This field inserts an #ifdef directive around the histogram's C++ declaration. This is typically used for platform-specific histograms, e.g. ``"cpp_guard": "ANDROID"``
 
+``operating_systems``
+---------------------
+Optional. This field restricts recording to certain operating systems only. Use that in-place of previous ``cpp_guards`` to avoid inclusion on not-specified operating systems.
+Currently supported values are:
+
+- ``mac``
+- ``linux``
+- ``windows``
+- ``android``
+- ``unix``
+- ``all`` (record on all operating systems)
+
+If this field is left out it defaults to ``all``.
+
 ``releaseChannelCollection``
 ----------------------------
 Optional. This is one of:
diff --git a/toolkit/components/telemetry/gen_histogram_data.py b/toolkit/components/telemetry/gen_histogram_data.py
index 9e28f9a6a9d6..7af76cc72e87 100644
--- a/toolkit/components/telemetry/gen_histogram_data.py
+++ b/toolkit/components/telemetry/gen_histogram_data.py
@@ -10,6 +10,7 @@ from shared_telemetry_utils import StringTable, static_assert, ParserError
 
 import sys
 import parse_histograms
+import buildconfig
 
 banner = """/* This file is auto-generated, see gen_histogram_data.py.  */
 """
@@ -17,26 +18,22 @@ banner = """/* This file is auto-generated, see gen_histogram_data.py.  */
 
 def print_array_entry(output, histogram, name_index, exp_index, label_index,
                       label_count, key_index, key_count):
-    cpp_guard = histogram.cpp_guard()
-    if cpp_guard:
-        print("#if defined(%s)" % cpp_guard, file=output)
-    print("  { %s, %s, %s, %s, %d, %d, %s, %d, %d, %d, %d, %s, %s, %s },"
-          % (histogram.low(),
-             histogram.high(),
-             histogram.n_buckets(),
-             histogram.nsITelemetry_kind(),
-             name_index,
-             exp_index,
-             histogram.dataset(),
-             label_index,
-             label_count,
-             key_index,
-             key_count,
-             " | ".join(histogram.record_in_processes_enum()),
-             "true" if histogram.keyed() else "false",
-             " | ".join(histogram.products_enum())), file=output)
-    if cpp_guard:
-        print("#endif", file=output)
+    if histogram.record_on_os(buildconfig.substs["OS_TARGET"]):
+        print("  { %s, %s, %s, %s, %d, %d, %s, %d, %d, %d, %d, %s, %s, %s },"
+              % (histogram.low(),
+                 histogram.high(),
+                 histogram.n_buckets(),
+                 histogram.nsITelemetry_kind(),
+                 name_index,
+                 exp_index,
+                 histogram.dataset(),
+                 label_index,
+                 label_count,
+                 key_index,
+                 key_count,
+                 " | ".join(histogram.record_in_processes_enum()),
+                 "true" if histogram.keyed() else "false",
+                 " | ".join(histogram.products_enum())), file=output)
 
 
 def write_histogram_table(output, histograms):
@@ -190,21 +187,17 @@ def write_histogram_ranges(output, histograms):
     if offset > 32767:
         raise Exception('Histogram offsets exceeded maximum value for an int16_t.')
 
+    target_os = buildconfig.substs["OS_TARGET"]
     print("#if defined(_MSC_VER) && !defined(__clang__)", file=output)
     print("const int16_t gHistogramBucketLowerBoundIndex[] = {", file=output)
     print("#else", file=output)
     print("constexpr int16_t gHistogramBucketLowerBoundIndex[] = {", file=output)
     print("#endif", file=output)
     for histogram in histograms:
-        cpp_guard = histogram.cpp_guard()
-        if cpp_guard:
-            print("#if defined(%s)" % cpp_guard, file=output)
+        if histogram.record_on_os(target_os):
+            our_offset = ranges_offsets[tuple(histogram.ranges())]
+            print("%d," % our_offset, file=output)
 
-        our_offset = ranges_offsets[tuple(histogram.ranges())]
-        print("%d," % our_offset, file=output)
-
-        if cpp_guard:
-            print("#endif", file=output)
     print("};", file=output)
 
 
diff --git a/toolkit/components/telemetry/gen_histogram_enum.py b/toolkit/components/telemetry/gen_histogram_enum.py
index 9b92ab5a33f1..9a9fde03431f 100644
--- a/toolkit/components/telemetry/gen_histogram_enum.py
+++ b/toolkit/components/telemetry/gen_histogram_enum.py
@@ -18,6 +18,7 @@ from shared_telemetry_utils import ParserError
 import parse_histograms
 import itertools
 import sys
+import buildconfig
 
 
 banner = """/* This file is auto-generated, see gen_histogram_enum.py.  */
@@ -72,12 +73,8 @@ def main(output, *filenames):
             print("  HistogramDUMMY1 = HistogramFirstUseCounter - 1,", file=output)
 
         for histogram in histograms:
-            cpp_guard = histogram.cpp_guard()
-            if cpp_guard:
-                print("#if defined(%s)" % cpp_guard, file=output)
-            print("  %s," % histogram.name(), file=output)
-            if cpp_guard:
-                print("#endif", file=output)
+            if histogram.record_on_os(buildconfig.substs["OS_TARGET"]):
+                print("  %s," % histogram.name(), file=output)
 
         if use_counter_group:
             print("  HistogramDUMMY2,", file=output)
diff --git a/toolkit/components/telemetry/gen_histogram_phf.py b/toolkit/components/telemetry/gen_histogram_phf.py
new file mode 100644
index 000000000000..f291f10f56dc
--- /dev/null
+++ b/toolkit/components/telemetry/gen_histogram_phf.py
@@ -0,0 +1,65 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+from __future__ import print_function
+from shared_telemetry_utils import ParserError
+from perfecthash import PerfectHash
+
+PHFSIZE = 512
+
+import parse_histograms
+import sys
+import buildconfig
+
+
+banner = """/* This file is auto-generated, see gen_histogram_phf.py.  */
+"""
+
+header = """
+#ifndef mozilla_TelemetryHistogramNameMap_h
+#define mozilla_TelemetryHistogramNameMap_h
+
+namespace mozilla {
+namespace Telemetry {
+"""
+
+footer = """
+} // namespace mozilla
+} // namespace Telemetry
+#endif // mozilla_TelemetryHistogramNameMap_h
+"""
+
+
+def main(output, *filenames):
+    """
+    Generate a Perfect Hash Table for the Histogram name -> Histogram ID lookup.
+    The table is immutable once generated and we can avoid any dynamic memory allocation.
+    """
+
+    output.write(banner)
+    output.write(header)
+
+    try:
+        histograms = list(parse_histograms.from_files(filenames))
+        histograms = [h for h in histograms if h.record_on_os(buildconfig.substs["OS_TARGET"])]
+    except ParserError as ex:
+        print("\nError processing histograms:\n" + str(ex) + "\n")
+        sys.exit(1)
+
+    histograms = [(bytearray(hist.name(), 'ascii'), idx) for (idx, hist) in enumerate(histograms)]
+    name_phf = PerfectHash(histograms, PHFSIZE)
+
+    output.write(name_phf.cxx_codegen(
+        name='HistogramIDByNameLookup',
+        entry_type="uint32_t",
+        lower_entry=lambda (_, v): str(v),
+        key_type="const nsACString&",
+        key_bytes="aKey.BeginReading()",
+        key_length="aKey.Length()"))
+
+    output.write(footer)
+
+
+if __name__ == '__main__':
+    main(sys.stdout, *sys.argv[1:])
diff --git a/toolkit/components/telemetry/moz.build b/toolkit/components/telemetry/moz.build
index f4bc8260a0f1..2bda9795ab40 100644
--- a/toolkit/components/telemetry/moz.build
+++ b/toolkit/components/telemetry/moz.build
@@ -121,6 +121,7 @@ GENERATED_FILES = [
     'TelemetryEventEnums.h',
     'TelemetryHistogramData.inc',
     'TelemetryHistogramEnums.h',
+    'TelemetryHistogramNameMap.h',
     'TelemetryProcessData.h',
     'TelemetryProcessEnums.h',
     'TelemetryScalarData.h',
@@ -142,6 +143,10 @@ enums = GENERATED_FILES['TelemetryHistogramEnums.h']
 enums.script = 'gen_histogram_enum.py'
 enums.inputs = histogram_files
 
+data = GENERATED_FILES['TelemetryHistogramNameMap.h']
+data.script = 'gen_histogram_phf.py'
+data.inputs = histogram_files
+
 # Generate scalar files.
 scalar_files = [
     'Scalars.yaml',
diff --git a/toolkit/components/telemetry/parse_histograms.py b/toolkit/components/telemetry/parse_histograms.py
index aeb27dba1171..a552d75283cd 100755
--- a/toolkit/components/telemetry/parse_histograms.py
+++ b/toolkit/components/telemetry/parse_histograms.py
@@ -28,7 +28,7 @@ CPP_IDENTIFIER_PATTERN = '^[a-z][a-z0-9_]+[a-z0-9]$'
 ALWAYS_ALLOWED_KEYS = [
     'kind',
     'description',
-    'cpp_guard',
+    'operating_systems',
     'expires_in_version',
     'alert_emails',
     'keyed',
@@ -122,10 +122,7 @@ definition is a dict-like object that must contain at least the keys:
  - 'description': A textual description of the histogram.
  - 'strict_type_checks': A boolean indicating whether to use the new, stricter type checks.
                          The server-side still has to deal with old, oddly typed submissions,
-                         so we have to skip them there by default.
-
-The key 'cpp_guard' is optional; if present, it denotes a preprocessor
-symbol that should guard C/C++ definitions associated with the histogram."""
+                         so we have to skip them there by default."""
         self._strict_type_checks = strict_type_checks
         self._is_use_counter = name.startswith("USE_COUNTER2_")
         if self._is_use_counter:
@@ -135,12 +132,12 @@ symbol that should guard C/C++ definitions associated with the histogram."""
         self._description = definition['description']
         self._kind = definition['kind']
         self._keys = definition.get('keys', [])
-        self._cpp_guard = definition.get('cpp_guard')
         self._keyed = definition.get('keyed', False)
         self._expiration = definition.get('expires_in_version')
         self._labels = definition.get('labels', [])
         self._record_in_processes = definition.get('record_in_processes')
         self._products = definition.get('products', ["all"])
+        self._operating_systems = definition.get('operating_systems', ["all"])
 
         self.compute_bucket_parameters(definition)
         self.set_nsITelemetry_kind()
@@ -181,11 +178,6 @@ the histogram."""
         """Return the number of buckets in the histogram."""
         return self._n_buckets
 
-    def cpp_guard(self):
-        """Return the preprocessor symbol that should guard C/C++ definitions
-associated with the histogram.  Returns None if no guarding is necessary."""
-        return self._cpp_guard
-
     def keyed(self):
         """Returns True if this a keyed histogram, false otherwise."""
         return self._keyed
@@ -218,6 +210,23 @@ associated with the histogram.  Returns None if no guarding is necessary."""
         """Get the non-empty list of flags representing products to record data on"""
         return [utils.product_name_to_enum(p) for p in self.products()]
 
+    def operating_systems(self):
+        """Get the list of operating systems to record data on"""
+        return self._operating_systems
+
+    def record_on_os(self, target_os):
+        """Check if this probe should be recorded on the passed os."""
+        os = self.operating_systems()
+        if "all" in os:
+            return True
+
+        canonical_os = utils.canonical_os(target_os)
+
+        if "unix" in os and canonical_os in utils.UNIX_LIKE_OS:
+            return True
+
+        return canonical_os in os
+
     def ranges(self):
         """Return an array of lower bounds for each bucket in the histogram."""
         bucket_fns = {
@@ -288,6 +297,7 @@ associated with the histogram.  Returns None if no guarding is necessary."""
         self.check_label_values(name, definition)
         self.check_record_in_processes(name, definition)
         self.check_products(name, definition)
+        self.check_operating_systems(name, definition)
 
     def check_name(self, name):
         if '#' in name:
@@ -393,6 +403,24 @@ associated with the histogram.  Returns None if no guarding is necessary."""
                 ParserError('Histogram "%s" has unknown product "%s" in %s.\n%s' %
                             (name, product, field, DOC_URL)).handle_later()
 
+    def check_operating_systems(self, name, definition):
+        if not self._strict_type_checks:
+            return
+
+        field = 'operating_systems'
+        operating_systems = definition.get(field)
+
+        DOC_URL = HISTOGRAMS_DOC_URL + "#operating_systems"
+
+        if not operating_systems:
+            # operating_systems is optional
+            return
+
+        for operating_system in operating_systems:
+            if not utils.is_valid_os(operating_system):
+                ParserError('Histogram "%s" has unknown operating system "%s" in %s.\n%s' %
+                            (name, operating_system, field, DOC_URL)).handle_later()
+
     def check_keys_field(self, name, definition):
         keys = definition.get('keys')
         if not self._strict_type_checks or keys is None:
@@ -422,10 +450,9 @@ associated with the histogram.  Returns None if no guarding is necessary."""
         # scalars instead. Allow using these histograms on Android, as we
         # don't support scalars there yet.
         hist_kind = definition.get("kind")
-        android_cpp_guard =\
-            definition.get("cpp_guard") in ["ANDROID", "MOZ_WIDGET_ANDROID"]
+        android_target = "android" in definition.get("operating_systems", [])
 
-        if not android_cpp_guard and \
+        if not android_target and \
            hist_kind in ["flag", "count"] and \
            name not in whitelists["kind"]:
             ParserError(('Unsupported kind "%s" for histogram "%s":\n'
@@ -433,7 +460,7 @@ associated with the histogram.  Returns None if no guarding is necessary."""
                          ' use scalars instead:\n'
                          '%s\n'
                          'Are you trying to add a histogram on Android?'
-                         ' Add "cpp_guard": "ANDROID" to your histogram definition.')
+                         ' Add "operating_systems": ["android"] to your histogram definition.')
                         % (hist_kind, name, hist_kind, SCALARS_DOC_URL)).handle_now()
 
     # Check for the presence of fields that old histograms are whitelisted for.
@@ -468,7 +495,6 @@ associated with the histogram.  Returns None if no guarding is necessary."""
             "expires_in_version": basestring,
             "kind": basestring,
             "description": basestring,
-            "cpp_guard": basestring,
             "releaseChannelCollection": basestring,
         }
 
@@ -480,6 +506,7 @@ associated with the histogram.  Returns None if no guarding is necessary."""
             "record_in_processes": basestring,
             "keys": basestring,
             "products": basestring,
+            "operating_systems": basestring,
         }
 
         # For the server-side, where _strict_type_checks==False, we want to
diff --git a/toolkit/components/telemetry/shared_telemetry_utils.py b/toolkit/components/telemetry/shared_telemetry_utils.py
index 6e6b1af22aff..dd461a3df669 100644
--- a/toolkit/components/telemetry/shared_telemetry_utils.py
+++ b/toolkit/components/telemetry/shared_telemetry_utils.py
@@ -30,6 +30,37 @@ SUPPORTED_PRODUCTS = {
     'all': 'All',
 }
 
+SUPPORTED_OPERATING_SYSTEMS = [
+    'mac',
+    'linux',
+    'windows',
+    'android',
+    'unix',
+    'all',
+]
+
+# mozinfo identifies linux, BSD variants, Solaris and SunOS as unix
+# Solaris and SunOS are identified as "unix" OS.
+UNIX_LIKE_OS = [
+    "unix",
+    "linux",
+    "bsd",
+]
+
+CANONICAL_OPERATING_SYSTEMS = {
+    'darwin': 'mac',
+    'linux': 'linux',
+    'winnt': 'windows',
+    'android': 'android',
+    # for simplicity we treat all BSD and Solaris systems as unix
+    'gnu/kfreebsd': 'unix',
+    'sunos': 'unix',
+    'dragonfly': 'unix',
+    'freeunix': 'unix',
+    'netunix': 'unix',
+    'openunix': 'unix'
+}
+
 PROCESS_ENUM_PREFIX = "mozilla::Telemetry::Common::RecordedProcessType::"
 PRODUCT_ENUM_PREFIX = "mozilla::Telemetry::Common::SupportedProduct::"
 
@@ -75,6 +106,16 @@ def is_valid_product(name):
     return (name in SUPPORTED_PRODUCTS)
 
 
+def is_valid_os(name):
+    return (name in SUPPORTED_OPERATING_SYSTEMS)
+
+
+def canonical_os(os):
+    """Translate possible OS_TARGET names to their canonical value."""
+
+    return CANONICAL_OPERATING_SYSTEMS.get(os.lower()) or "unknown"
+
+
 def product_name_to_enum(product):
     return PRODUCT_ENUM_PREFIX + SUPPORTED_PRODUCTS.get(product)
 
diff --git a/toolkit/components/telemetry/tests/unit/test_TelemetryHistograms.js b/toolkit/components/telemetry/tests/unit/test_TelemetryHistograms.js
index 9e34de6ac7d0..7a43d3547b39 100644
--- a/toolkit/components/telemetry/tests/unit/test_TelemetryHistograms.js
+++ b/toolkit/components/telemetry/tests/unit/test_TelemetryHistograms.js
@@ -1197,3 +1197,42 @@ async function test_clearHistogramsOnSnapshot() {
                                               false /* clear */).parent;
   Assert.ok(!(COUNT in snapshot));
 });
+
+add_task(async function test_valid_os_smoketest() {
+  let nonExistingProbe;
+  let existingProbe;
+
+  switch (AppConstants.platform) {
+    case "linux":
+      nonExistingProbe = "TELEMETRY_TEST_OS_ANDROID_ONLY";
+      existingProbe = "TELEMETRY_TEST_OS_LINUX_ONLY";
+      break;
+    case "macosx":
+      nonExistingProbe = "TELEMETRY_TEST_OS_ANDROID_ONLY";
+      existingProbe = "TELEMETRY_TEST_OS_MAC_ONLY";
+      break;
+    case "win":
+      nonExistingProbe = "TELEMETRY_TEST_OS_ANDROID_ONLY";
+      existingProbe = "TELEMETRY_TEST_OS_WIN_ONLY";
+      break;
+    case "android":
+      nonExistingProbe = "TELEMETRY_TEST_OS_LINUX_ONLY";
+      existingProbe = "TELEMETRY_TEST_OS_ANDROID_ONLY";
+      break;
+    default:
+      /* Unknown OS. Let's not test OS-specific probes */
+      return;
+  }
+
+  Assert.throws(() => Telemetry.getHistogramById(nonExistingProbe),
+    /NS_ERROR_FAILURE/,
+    `Should throw on ${nonExistingProbe} probe that's not available on ${AppConstants.platform}`);
+
+  let h = Telemetry.getHistogramById(existingProbe);
+  h.clear();
+  h.add(1);
+  let snapshot = Telemetry.snapshotHistograms(Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTIN,
+                                              false /* clear */).parent;
+  Assert.ok(existingProbe in snapshot, `${existingProbe} should be recorded on ${AppConstants.platform}`);
+  Assert.equal(snapshot[existingProbe].sum, 1);
+});
diff --git a/toolkit/components/telemetry/tests/unit/test_TelemetrySession.js b/toolkit/components/telemetry/tests/unit/test_TelemetrySession.js
index e9e45dee65fb..7ffac74976b5 100644
--- a/toolkit/components/telemetry/tests/unit/test_TelemetrySession.js
+++ b/toolkit/components/telemetry/tests/unit/test_TelemetrySession.js
@@ -1032,8 +1032,6 @@ add_task(async function test_sendShutdownPing() {
     return;
   }
 
-  const OSSHUTDOWN_SCALAR = "telemetry.os_shutting_down";
-
   let checkPendingShutdownPing = async function() {
     let pendingPings = await TelemetryStorage.loadPendingPingList();
     Assert.equal(pendingPings.length, 1,
@@ -1043,8 +1041,6 @@ add_task(async function test_sendShutdownPing() {
     Assert.ok(shutdownPing, "The 'shutdown' ping must be saved to disk.");
     Assert.equal("shutdown", shutdownPing.payload.info.reason,
                  "The 'shutdown' ping must be saved to disk.");
-    Assert.ok(shutdownPing.payload.processes.parent.scalars[OSSHUTDOWN_SCALAR],
-              "The OS shutdown scalar must be set to true.");
   };
 
   Preferences.set(TelemetryUtils.Preferences.ShutdownPingSender, true);
@@ -1063,8 +1059,6 @@ add_task(async function test_sendShutdownPing() {
   checkPingFormat(ping, ping.type, true, true);
   Assert.equal(ping.payload.info.reason, REASON_SHUTDOWN);
   Assert.equal(ping.clientId, gClientID);
-  Assert.ok(!(OSSHUTDOWN_SCALAR in ping.payload.processes.parent.scalars),
-            "The OS shutdown scalar must not be set.");
   // Try again, this time disable ping upload. The PingSender
   // should not be sending any ping!
   PingServer.registerPingHandler(() => Assert.ok(false, "Telemetry must not send pings if not allowed to."));
diff --git a/toolkit/components/url-classifier/nsUrlClassifierUtils.cpp b/toolkit/components/url-classifier/nsUrlClassifierUtils.cpp
index ce445d4a473e..036e69f3e3e8 100644
--- a/toolkit/components/url-classifier/nsUrlClassifierUtils.cpp
+++ b/toolkit/components/url-classifier/nsUrlClassifierUtils.cpp
@@ -19,6 +19,7 @@
 #include "nsIHttpChannelInternal.h"
 #include "mozIThirdPartyUtil.h"
 #include "nsIDocShell.h"
+#include "mozilla/TextUtils.h"
 
 #define DEFAULT_PROTOCOL_VERSION "2.2"
 
@@ -32,7 +33,7 @@ static bool
 IsDecimal(const nsACString & num)
 {
   for (uint32_t i = 0; i < num.Length(); i++) {
-    if (!isdigit(num[i])) {
+    if (!mozilla::IsAsciiDigit(num[i])) {
       return false;
     }
   }
@@ -52,7 +53,7 @@ IsHex(const nsACString & num)
   }
 
   for (uint32_t i = 2; i < num.Length(); i++) {
-    if (!isxdigit(num[i])) {
+    if (!mozilla::IsAsciiHexDigit(num[i])) {
       return false;
     }
   }
@@ -72,7 +73,7 @@ IsOctal(const nsACString & num)
   }
 
   for (uint32_t i = 1; i < num.Length(); i++) {
-    if (!isdigit(num[i]) || num[i] == '8' || num[i] == '9') {
+    if (!mozilla::IsAsciiDigit(num[i]) || num[i] == '8' || num[i] == '9') {
       return false;
     }
   }
@@ -947,7 +948,7 @@ nsUrlClassifierUtils::ParseIPAddress(const nsACString & host,
   }
 
   for (host.BeginReading(iter); iter != end; iter++) {
-    if (!(isxdigit(*iter) || *iter == 'x' || *iter == 'X' || *iter == '.')) {
+    if (!(mozilla::IsAsciiHexDigit(*iter) || *iter == 'x' || *iter == 'X' || *iter == '.')) {
       // not an IP
       return;
     }
diff --git a/toolkit/moz.configure b/toolkit/moz.configure
index e1a361d19b7f..78f9e2ac9b32 100644
--- a/toolkit/moz.configure
+++ b/toolkit/moz.configure
@@ -1064,3 +1064,16 @@ def launcher(value, target):
 
 set_config('MOZ_LAUNCHER_PROCESS', launcher)
 set_define('MOZ_LAUNCHER_PROCESS', launcher)
+
+# Prio
+# ==============================================================
+@depends(c_compiler)
+def libprio(info):
+    if info:
+      if info.type in ('msvc'):
+        return None
+    else:
+      return True
+
+set_config('MOZ_LIBPRIO', libprio)
+
diff --git a/toolkit/themes/shared/in-content/common.inc.css b/toolkit/themes/shared/in-content/common.inc.css
index 7fe51e157b4e..f16620e4ea67 100644
--- a/toolkit/themes/shared/in-content/common.inc.css
+++ b/toolkit/themes/shared/in-content/common.inc.css
@@ -506,12 +506,13 @@ xul|textbox[focused] {
   border-color: var(--in-content-border-focus);
 }
 
-/* Don't show the field error outlines and focus borders at the same time */
+/* Don't show the field error outlines and focus borders at the same time.
+   This doesn't apply to XUL <textbox> since they don't expose validity
+   attributes */
 html|input[type="email"]:-moz-ui-invalid:focus,
 html|input[type="tel"]:-moz-ui-invalid:focus,
 html|input[type="text"]:-moz-ui-invalid:focus,
-html|textarea:-moz-ui-invalid:focus,
-xul|textbox[focused] {
+html|textarea:-moz-ui-invalid:focus {
   border-color: transparent;
 }
 
diff --git a/tools/lint/docs/create.rst b/tools/lint/docs/create.rst
index 8f1dcf18149b..653440c28c8a 100644
--- a/tools/lint/docs/create.rst
+++ b/tools/lint/docs/create.rst
@@ -54,7 +54,7 @@ external.  External linters call an arbitrary python function which is
 responsible for not only running the linter, but ensuring the results
 are structured properly. For example, an external type could shell out
 to a 3rd party linter, collect the output and format it into a list of
-:class:`ResultContainer` objects. The signature for this python
+:class:`Issue` objects. The signature for this python
 function is ``lint(files, config, **kwargs)``, where ``files`` is a list of
 files to lint and ``config`` is the linter definition defined in the ``.yml``
 file.
@@ -129,7 +129,7 @@ let's call the file ``flake8_lint.py``:
 
         # Flake8 allows passing in a custom format string. We use
         # this to help mold the default flake8 format into what
-        # mozlint's ResultContainer object expects.
+        # mozlint's Issue object expects.
         cmdargs = [
             binary,
             '--format',
@@ -153,7 +153,7 @@ let's call the file ``flake8_lint.py``:
                 res['level'] = 'warning'
 
             # result.from_linter is a convenience method that
-            # creates a ResultContainer using a LINTER definition
+            # creates a Issue using a LINTER definition
             # to populate some defaults.
             results.append(result.from_config(config, **res))
 
diff --git a/tools/lint/python/__init__.py b/tools/lint/python/__init__.py
index f79d8d363a72..1327d37ebadd 100644
--- a/tools/lint/python/__init__.py
+++ b/tools/lint/python/__init__.py
@@ -52,7 +52,7 @@ LINE_OFFSETS = {
 """Maps a flake8 error to a lineoffset tuple.
 
 The offset is of the form (lineno_offset, num_lines) and is passed
-to the lineoffset property of `ResultContainer`.
+to the lineoffset property of an `Issue`.
 """
 
 results = []
diff --git a/tools/lint/python/flake8.py b/tools/lint/python/flake8.py
index 1d56be020819..0abb6b2d486c 100644
--- a/tools/lint/python/flake8.py
+++ b/tools/lint/python/flake8.py
@@ -54,7 +54,7 @@ LINE_OFFSETS = {
 """Maps a flake8 error to a lineoffset tuple.
 
 The offset is of the form (lineno_offset, num_lines) and is passed
-to the lineoffset property of `ResultContainer`.
+to the lineoffset property of an `Issue`.
 """
 
 # We use sys.prefix to find executables as that gets modified with
diff --git a/tools/rewriting/ThirdPartyPaths.txt b/tools/rewriting/ThirdPartyPaths.txt
index d88e671aaaeb..7229f3ebcc83 100644
--- a/tools/rewriting/ThirdPartyPaths.txt
+++ b/tools/rewriting/ThirdPartyPaths.txt
@@ -5,6 +5,10 @@ devtools/client/sourceeditor/codemirror/
 devtools/client/sourceeditor/tern/
 devtools/shared/heapsnapshot/CoreDump.pb.cc
 devtools/shared/heapsnapshot/CoreDump.pb.h
+dom/media/gmp/widevine-adapter/content_decryption_module.h
+dom/media/gmp/widevine-adapter/content_decryption_module_export.h
+dom/media/gmp/widevine-adapter/content_decryption_module_ext.h
+dom/media/gmp/widevine-adapter/content_decryption_module_proxy.h
 editor/libeditor/tests/browserscope/lib/richtext/
 editor/libeditor/tests/browserscope/lib/richtext2/
 extensions/spellcheck/hunspell/src/
diff --git a/xpcom/build/LateWriteChecks.cpp b/xpcom/build/LateWriteChecks.cpp
index 8ef30a567093..1dbe7110fe39 100644
--- a/xpcom/build/LateWriteChecks.cpp
+++ b/xpcom/build/LateWriteChecks.cpp
@@ -133,8 +133,7 @@ LateWriteObserver::Observe(IOInterposeObserver::Observation& aOb)
 
   nsTAutoString<char_type> nameAux(mProfileDirectory);
   nameAux.AppendLiteral(NS_SLASH "Telemetry.LateWriteTmpXXXXXX");
-  char_type* name;
-  nameAux.GetMutableData(&name);
+  char_type* name = nameAux.BeginWriting();
 
   // We want the sha1 of the entire file, so please don't write to fd
   // directly; use sha1Stream.
diff --git a/xpcom/string/nsReadableUtils.h b/xpcom/string/nsReadableUtils.h
index 31d326b5b14e..0523f2fcbbbf 100644
--- a/xpcom/string/nsReadableUtils.h
+++ b/xpcom/string/nsReadableUtils.h
@@ -88,7 +88,8 @@ extern "C" {
   nsstring_fallible_append_latin1_impl(nsAString* aThis,
                                        const char* aOther,
                                        size_t aOtherLen,
-                                       size_t aOldLen);
+                                       size_t aOldLen,
+                                       bool aAllowShrinking);
 
   bool
   nscstring_fallible_append_utf16_to_utf8_impl(nsACString* aThis,
@@ -100,7 +101,8 @@ extern "C" {
   nscstring_fallible_append_utf16_to_latin1_lossy_impl(nsACString* aThis,
                                                        const char16_t*,
                                                        size_t aOtherLen,
-                                                       size_t aOldLen);
+                                                       size_t aOldLen,
+                                                       bool aAllowShrinking);
 
   bool
   nscstring_fallible_append_utf8_to_latin1_lossy_check(nsACString* aThis,
@@ -256,7 +258,7 @@ CopyASCIItoUTF16(mozilla::Span<const char> aSource,
                  const mozilla::fallible_t&)
 {
   return nsstring_fallible_append_latin1_impl(
-    &aDest, aSource.Elements(), aSource.Length(), 0);
+    &aDest, aSource.Elements(), aSource.Length(), 0, true);
 }
 
 inline void
@@ -273,7 +275,7 @@ AppendASCIItoUTF16(mozilla::Span<const char> aSource,
                    const mozilla::fallible_t&)
 {
   return nsstring_fallible_append_latin1_impl(
-    &aDest, aSource.Elements(), aSource.Length(), aDest.Length());
+    &aDest, aSource.Elements(), aSource.Length(), aDest.Length(), false);
 }
 
 inline void
@@ -335,7 +337,7 @@ LossyCopyUTF16toASCII(mozilla::Span<const char16_t> aSource,
                       const mozilla::fallible_t&)
 {
   return nscstring_fallible_append_utf16_to_latin1_lossy_impl(
-    &aDest, aSource.Elements(), aSource.Length(), 0);
+    &aDest, aSource.Elements(), aSource.Length(), 0, true);
 }
 
 inline void
@@ -352,7 +354,7 @@ LossyAppendUTF16toASCII(mozilla::Span<const char16_t> aSource,
                         const mozilla::fallible_t&)
 {
   return nscstring_fallible_append_utf16_to_latin1_lossy_impl(
-    &aDest, aSource.Elements(), aSource.Length(), aDest.Length());
+    &aDest, aSource.Elements(), aSource.Length(), aDest.Length(), false);
 }
 
 inline void
diff --git a/xpcom/string/nsSubstring.cpp b/xpcom/string/nsSubstring.cpp
index 1fa823f51573..653d93bad11e 100644
--- a/xpcom/string/nsSubstring.cpp
+++ b/xpcom/string/nsSubstring.cpp
@@ -465,7 +465,7 @@ Gecko_StartBulkWriteCString(nsACString* aThis,
                             uint32_t aUnitsToPreserve,
                             bool aAllowShrinking)
 {
-  return aThis->StartBulkWrite(aCapacity, aUnitsToPreserve, aAllowShrinking).unwrapOr(UINT32_MAX);
+  return aThis->StartBulkWriteImpl(aCapacity, aUnitsToPreserve, aAllowShrinking).unwrapOr(UINT32_MAX);
 }
 
 void Gecko_FinalizeString(nsAString* aThis)
@@ -529,7 +529,7 @@ Gecko_StartBulkWriteString(nsAString* aThis,
                            uint32_t aUnitsToPreserve,
                            bool aAllowShrinking)
 {
-  return aThis->StartBulkWrite(aCapacity, aUnitsToPreserve, aAllowShrinking).unwrapOr(UINT32_MAX);
+  return aThis->StartBulkWriteImpl(aCapacity, aUnitsToPreserve, aAllowShrinking).unwrapOr(UINT32_MAX);
 }
 
 } // extern "C"
diff --git a/xpcom/string/nsTStringObsolete.cpp b/xpcom/string/nsTStringObsolete.cpp
index e269841deb7e..7b77617a2a9b 100644
--- a/xpcom/string/nsTStringObsolete.cpp
+++ b/xpcom/string/nsTStringObsolete.cpp
@@ -327,7 +327,7 @@ nsTString<T>::ReplaceSubstring(const self_type& aTarget,
   // string.  In other words, we over-allocate in the shrinking case.
   uint32_t oldLen = this->mLength;
   mozilla::Result<uint32_t, nsresult> r =
-    this->StartBulkWrite(XPCOM_MAX(oldLen, newLength.value()), oldLen);
+    this->StartBulkWriteImpl(XPCOM_MAX(oldLen, newLength.value()), oldLen);
   if (r.isErr()) {
     return false;
   }
@@ -367,7 +367,7 @@ nsTString<T>::ReplaceSubstring(const self_type& aTarget,
   }
 
   // Adjust the length and make sure the string is null terminated.
-  this->FinishBulkWrite(newLength.value());
+  this->FinishBulkWriteImpl(newLength.value());
 
   return true;
 }
diff --git a/xpcom/string/nsTSubstring.cpp b/xpcom/string/nsTSubstring.cpp
index 930b98f3e818..580795546407 100644
--- a/xpcom/string/nsTSubstring.cpp
+++ b/xpcom/string/nsTSubstring.cpp
@@ -65,14 +65,33 @@ AsAutoString(const nsTSubstring<T>* aStr)
   return static_cast<const nsTAutoString<T>*>(aStr);
 }
 
+template<typename T>
+mozilla::BulkWriteHandle<T>
+nsTSubstring<T>::BulkWrite(size_type aCapacity,
+                           size_type aPrefixToPreserve,
+                           bool aAllowShrinking,
+                           nsresult& aRv)
+{
+  auto r = StartBulkWriteImpl(aCapacity,
+                              aPrefixToPreserve,
+                              aAllowShrinking);
+  if (MOZ_UNLIKELY(r.isErr())) {
+    aRv = r.unwrapErr();
+    return mozilla::BulkWriteHandle<T>(nullptr, 0);
+  }
+  aRv = NS_OK;
+  return mozilla::BulkWriteHandle<T>(this, r.unwrap());
+}
+
+
 template<typename T>
 mozilla::Result<uint32_t, nsresult>
-nsTSubstring<T>::StartBulkWrite(size_type aCapacity,
-                                size_type aPrefixToPreserve,
-                                bool aAllowShrinking,
-                                size_type aSuffixLength,
-                                size_type aOldSuffixStart,
-                                size_type aNewSuffixStart)
+nsTSubstring<T>::StartBulkWriteImpl(size_type aCapacity,
+                                    size_type aPrefixToPreserve,
+                                    bool aAllowShrinking,
+                                    size_type aSuffixLength,
+                                    size_type aOldSuffixStart,
+                                    size_type aNewSuffixStart)
 {
   // Note! Capacity does not include room for the terminating null char.
 
@@ -180,22 +199,21 @@ nsTSubstring<T>::StartBulkWrite(size_type aCapacity,
       // bucket, it's not useful to use realloc, which may spend time uselessly
       // copying too much.
       nsStringBuffer* newHdr = nsStringBuffer::Alloc(storageSize).take();
-      if (!newHdr) {
-        // we are still in a consistent state
-        if (shrinking) {
-          // Since shrinking is just a memory footprint optimization, we
-          // don't propagate OOM if we tried to shrink in order to avoid
-          // OOM crashes from infallible callers. If we're lucky, soon enough
-          // a fallible caller reaches OOM and is able to deal or we end up
-          // disposing of this string before reaching OOM again.
-          newData = oldData;
-          newCapacity = curCapacity;
-        } else {
-          return mozilla::Err(NS_ERROR_OUT_OF_MEMORY);
-        }
+      if (newHdr) {
+        newData = (char_type*)newHdr->Data();
+      } else if (shrinking) {
+        // We're still in a consistent state.
+        //
+        // Since shrinking is just a memory footprint optimization, we
+        // don't propagate OOM if we tried to shrink in order to avoid
+        // OOM crashes from infallible callers. If we're lucky, soon enough
+        // a fallible caller reaches OOM and is able to deal or we end up
+        // disposing of this string before reaching OOM again.
+        newData = oldData;
+        newCapacity = curCapacity;
+      } else {
+        return mozilla::Err(NS_ERROR_OUT_OF_MEMORY);
       }
-
-      newData = (char_type*)newHdr->Data();
     }
     newDataFlags = DataFlags::TERMINATED | DataFlags::REFCOUNTED;
   }
@@ -218,7 +236,7 @@ nsTSubstring<T>::StartBulkWrite(size_type aCapacity,
 
 template<typename T>
 void
-nsTSubstring<T>::FinishBulkWrite(size_type aLength)
+nsTSubstring<T>::FinishBulkWriteImpl(size_type aLength)
 {
   MOZ_ASSERT(aLength != UINT32_MAX, "OOM magic value passed as length.");
   if (aLength) {
@@ -274,12 +292,12 @@ nsTSubstring<T>::ReplacePrepInternal(index_type aCutStart, size_type aCutLen,
   size_type oldSuffixStart = aCutStart + aCutLen;
   size_type suffixLength = this->mLength - oldSuffixStart;
 
-  mozilla::Result<uint32_t, nsresult> r = StartBulkWrite(
+  mozilla::Result<uint32_t, nsresult> r = StartBulkWriteImpl(
     aNewLen, aCutStart, false, suffixLength, oldSuffixStart, newSuffixStart);
   if (r.isErr()) {
     return false;
   }
-  FinishBulkWrite(aNewLen);
+  FinishBulkWriteImpl(aNewLen);
   return true;
 }
 
@@ -566,14 +584,14 @@ nsTSubstring<T>::Assign(const substring_tuple_type& aTuple,
 
   size_type length = aTuple.Length();
 
-  mozilla::Result<uint32_t, nsresult> r = StartBulkWrite(length);
+  mozilla::Result<uint32_t, nsresult> r = StartBulkWriteImpl(length);
   if (r.isErr()) {
     return false;
   }
 
   aTuple.WriteTo(this->mData, length);
 
-  FinishBulkWrite(length);
+  FinishBulkWriteImpl(length);
   return true;
 }
 
@@ -789,7 +807,7 @@ nsTSubstring<T>::SetCapacity(size_type aCapacity, const fallible_t&)
     preserve = aCapacity;
   }
 
-  mozilla::Result<uint32_t, nsresult> r = StartBulkWrite(aCapacity, preserve);
+  mozilla::Result<uint32_t, nsresult> r = StartBulkWriteImpl(aCapacity, preserve);
   if (r.isErr()) {
     return false;
   }
diff --git a/xpcom/string/nsTSubstring.h b/xpcom/string/nsTSubstring.h
index 377d52ab89cb..9f4d17ec0df7 100644
--- a/xpcom/string/nsTSubstring.h
+++ b/xpcom/string/nsTSubstring.h
@@ -15,6 +15,7 @@
 #include "mozilla/IntegerTypeTraits.h"
 #include "mozilla/Result.h"
 #include "mozilla/Span.h"
+#include "mozilla/Unused.h"
 
 #include "nsTStringRepr.h"
 
@@ -24,6 +25,264 @@
 
 template <typename T> class nsTSubstringSplitter;
 template <typename T> class nsTString;
+template <typename T> class nsTSubstring;
+
+namespace mozilla {
+
+/**
+ * This handle represents permission to perform low-level writes
+ * the storage buffer of a string in a manner that's aware of the
+ * actual capacity of the storage buffer allocation and that's
+ * cache-friendly in the sense that the writing of zero terminator
+ * for C compatibility can happen in linear memory access order
+ * (i.e. the zero terminator write takes place after writing
+ * new content to the string as opposed to the zero terminator
+ * write happening first causing a non-linear memory write for
+ * cache purposes).
+ *
+ * If you requested a prefix to be preserved when starting
+ * or restarting the bulk write, the prefix is present at the
+ * start of the buffer exposed by this handle as Span or
+ * as a raw pointer, and it's your responsibility to start
+ * writing after after the preserved prefix (which you
+ * presumably wanted not to overwrite since you asked for
+ * it to be preserved).
+ *
+ * In a success case, you must call Finish() with the new
+ * length of the string. In failure cases, it's OK to return
+ * early from the function whose local variable this handle is.
+ * The destructor of this class takes care of putting the
+ * string in a valid and mostly harmless state in that case
+ * by setting the value of a non-empty string to a single
+ * REPLACEMENT CHARACTER or in the case of nsACString that's
+ * too short for a REPLACEMENT CHARACTER to fit, an ASCII
+ * SUBSTITUTE.
+ *
+ * You must not allow this handle to outlive the string you
+ * obtained it from.
+ *
+ * You must not access the string you obtained this handle
+ * from in any way other than through this handle until
+ * you call Finish() on the handle or the handle goes out
+ * of scope.
+ *
+ * Once you've called Finish(), you must not call any
+ * methods on this handle and must not use values previously
+ * obtained.
+ *
+ * Once you call RestartBulkWrite(), you must not use
+ * values previously obtained from this handle and must
+ * reobtain the new corresponding values.
+ */
+template <typename T>
+class BulkWriteHandle final {
+  friend class nsTSubstring<T>;
+public:
+  typedef typename mozilla::detail::nsTStringRepr<T> base_string_type;
+  typedef typename base_string_type::size_type size_type;
+
+  /**
+   * Pointer to the start of the writable buffer. Never nullptr.
+   *
+   * This pointer is valid until whichever of these happens first:
+   *  1) Finish() is called
+   *  2) RestartBulkWrite() is called
+   *  3) BulkWriteHandle goes out of scope
+   */
+  T* Elements() const
+  {
+    MOZ_ASSERT(mString);
+    return mString->mData;
+  }
+
+  /**
+   * How many code units can be written to the buffer.
+   * (Note: This is not the same as the string's Length().)
+   *
+   * This value is valid until whichever of these happens first:
+   *  1) Finish() is called
+   *  2) RestartBulkWrite() is called
+   *  3) BulkWriteHandle goes out of scope
+   */
+  size_type Length() const
+  {
+    MOZ_ASSERT(mString);
+    return mCapacity;
+  }
+
+  /**
+   * Pointer past the end of the buffer.
+   *
+   * This pointer is valid until whichever of these happens first:
+   *  1) Finish() is called
+   *  2) RestartBulkWrite() is called
+   *  3) BulkWriteHandle goes out of scope
+   */
+  T* End() const
+  {
+    return Elements() + Length();
+  }
+
+  /**
+   * The writable buffer as Span.
+   *
+   * This Span is valid until whichever of these happens first:
+   *  1) Finish() is called
+   *  2) RestartBulkWrite() is called
+   *  3) BulkWriteHandle goes out of scope
+   */
+  mozilla::Span<T> AsSpan() const
+  {
+    return mozilla::MakeSpan(Elements(), Length());
+  }
+
+  /**
+   * Autoconvert to the buffer as writable Span.
+   *
+   * This Span is valid until whichever of these happens first:
+   *  1) Finish() is called
+   *  2) RestartBulkWrite() is called
+   *  3) BulkWriteHandle goes out of scope
+   */
+  operator mozilla::Span<T>() const
+  {
+    return AsSpan();
+  }
+
+  /**
+   * Restart the bulk write with a different capacity.
+   *
+   * This method invalidates previous return values
+   * of the other methods above.
+   *
+   * Can fail if out of memory leaving the buffer
+   * in the state before this call.
+   *
+   * @param aCapacity the new requested capacity
+   * @param aPrefixToPreserve the number of code units at
+   *                          the start of the string to
+   *                          copy over to the new buffer
+   * @param aAllowShrinking whether the string is
+   *                        allowed to attempt to
+   *                        allocate a smaller buffer
+   *                        for its content and copy
+   *                        the data over.
+   */
+  mozilla::Result<mozilla::Ok, nsresult> RestartBulkWrite(size_type aCapacity,
+                                                          size_type aPrefixToPreserve,
+                                                          bool aAllowShrinking)
+  {
+    MOZ_ASSERT(mString);
+    auto r = mString->StartBulkWriteImpl(aCapacity, aPrefixToPreserve, aAllowShrinking);
+    if (MOZ_UNLIKELY(r.isErr())) {
+      nsresult rv = r.unwrapErr();
+      // MOZ_TRY or manual unwrapErr() without the intermediate
+      // assignment complains about an incomplete type.
+      // andThen() is not enabled on r.
+      return mozilla::Err(rv);
+    }
+    mCapacity = r.unwrap();
+    return mozilla::Ok();
+  }
+
+  /**
+   * Indicate that the bulk write finished successfully.
+   *
+   * @param aLength the number of code units written;
+   *                must not exceed Length()
+   * @param aAllowShrinking whether the string is
+   *                        allowed to attempt to
+   *                        allocate a smaller buffer
+   *                        for its content and copy
+   *                        the data over.
+   */
+  void Finish(size_type aLength, bool aAllowShrinking)
+  {
+    MOZ_ASSERT(mString);
+    MOZ_ASSERT(aLength <= mCapacity);
+    if (!aLength) {
+      // Truncate is safe even when the string is in an invalid state
+      mString->Truncate();
+      mString = nullptr;
+      return;
+    }
+    if (aAllowShrinking) {
+      mozilla::Unused << mString->StartBulkWriteImpl(aLength, aLength, true);
+    }
+    mString->FinishBulkWriteImpl(aLength);
+    mString = nullptr;
+  }
+
+  BulkWriteHandle(BulkWriteHandle&& aOther)
+   : mString(aOther.Forget())
+   , mCapacity(aOther.mCapacity)
+  {
+  }
+
+  ~BulkWriteHandle()
+  {
+    if (!mString || !mCapacity) {
+      return;
+    }
+    // The old zero terminator may be gone by now, so we need
+    // to write a new one somewhere and make length match.
+    // We can use a length between 1 and self.capacity.
+    // The contents of the string can be partially uninitialized
+    // or partially initialized in a way that would be dangerous
+    // if parsed by some recipient. It's prudent to write something
+    // same as the contents of the string. U+FFFD is the safest
+    // placeholder, but when it doesn't fit, let's use ASCII
+    // substitute. Merely truncating the string to a zero-length
+    // string might be dangerous in some scenarios. See
+    // https://www.unicode.org/reports/tr36/#Substituting_for_Ill_Formed_Subsequences
+    // for closely related scenario.
+    auto ptr = Elements();
+    // Cast the pointer below to silence warnings
+    if (sizeof(T) == 1) {
+      unsigned char* charPtr = reinterpret_cast<unsigned char*>(ptr);
+      if (mCapacity >= 3) {
+        *charPtr++ = 0xEF;
+        *charPtr++ = 0xBF;
+        *charPtr++ = 0xBD;
+        mString->mLength = 3;
+      } else {
+        *charPtr++ = 0x1A;
+        mString->mLength = 1;
+      }
+      *charPtr = 0;
+    } else if (sizeof(T) == 2){
+      char16_t* charPtr = reinterpret_cast<char16_t*>(ptr);
+      *charPtr++ = 0xFFFD;
+      *charPtr = 0;
+      mString->mLength = 1;
+    } else {
+      MOZ_ASSERT_UNREACHABLE("Only 8-bit and 16-bit code units supported.");
+    }
+  }
+
+  BulkWriteHandle() = delete;
+  BulkWriteHandle(const BulkWriteHandle&) = delete;
+  BulkWriteHandle& operator=(const BulkWriteHandle&) = delete;
+
+private:
+
+  BulkWriteHandle(nsTSubstring<T>* aString, size_type aCapacity)
+   : mString(aString)
+   , mCapacity(aCapacity)
+  {}
+
+  nsTSubstring<T>* Forget()
+  {
+    auto string = mString;
+    mString = nullptr;
+    return string;
+  }
+
+  nsTSubstring<T>* mString; // nullptr upon finish
+  size_type        mCapacity;
+};
+
+} // namespace mozilla
 
 /**
  * nsTSubstring is an abstract string class. From an API perspective, this
@@ -40,6 +299,7 @@ template <typename T> class nsTString;
 template <typename T>
 class nsTSubstring : public mozilla::detail::nsTStringRepr<T>
 {
+  friend class mozilla::BulkWriteHandle<T>;
 public:
   typedef nsTSubstring<T> self_type;
 
@@ -79,6 +339,9 @@ public:
 
   /**
    * writing iterators
+   *
+   * Note: Consider if BulkWrite() suits your use case better
+   * than BeginWriting() combined with SetLength().
    */
 
   char_iterator BeginWriting()
@@ -888,6 +1151,50 @@ protected:
   void NS_FASTCALL Finalize();
 
 public:
+
+  /**
+   * Starts a low-level write transaction to the string.
+   *
+   * Prepares the string for mutation such that the capacity
+   * of the string is at least aCapacity. The returned handle
+   * exposes the actual, potentially larger, capacity.
+   *
+   * If meeting the capacity or mutability requirement requires
+   * reallocation, aPrefixToPreserve code units are copied from the
+   * start of the old buffer to the start of the new buffer.
+   * aPrefixToPreserve must not be greater than the string's current
+   * length or greater than aCapacity.
+   *
+   * aAllowShrinking indicates whether an allocation may be
+   * performed when the string is already mutable and the requested
+   * capacity is smaller than the current capacity.
+   *
+   * aRv takes a reference to an nsresult that will be set to
+   * NS_OK on success or to NS_ERROR_OUT_OF_MEMORY on failure,
+   * because mozilla::Result cannot wrap move-only types at
+   * this time.
+   *
+   * If this method returns successfully, you must not access
+   * the string except through the returned BulkWriteHandle
+   * until either the BulkWriteHandle goes out of scope or
+   * you call Finish() on the BulkWriteHandle.
+   *
+   * Compared to SetLength() and BeginWriting(), this more
+   * complex API accomplishes two things:
+   *  1) It exposes the actual capacity which may be larger
+   *     than the requested capacity, which is useful in some
+   *     multi-step write operations that don't allocate for
+   *     the worst case up front.
+   *  2) It writes the zero terminator after the string
+   *     content has been written, which results in a
+   *     cache-friendly linear write pattern.
+   */
+  mozilla::BulkWriteHandle<T>
+  NS_FASTCALL BulkWrite(size_type aCapacity,
+                        size_type aPrefixToPreserve,
+                        bool aAllowShrinking,
+                        nsresult& aRv);
+
   /**
    * THIS IS NOT REALLY A PUBLIC METHOD! DO NOT CALL FROM OUTSIDE
    * THE STRING IMPLEMENTATION. (It's public only because friend
@@ -936,12 +1243,12 @@ public:
    *
    */
   mozilla::Result<uint32_t, nsresult>
-  NS_FASTCALL StartBulkWrite(size_type aCapacity,
-                             size_type aPrefixToPreserve = 0,
-                             bool aAllowShrinking = true,
-                             size_type aSuffixLength = 0,
-                             size_type aOldSuffixStart = 0,
-                             size_type aNewSuffixStart = 0);
+  NS_FASTCALL StartBulkWriteImpl(size_type aCapacity,
+                                 size_type aPrefixToPreserve = 0,
+                                 bool aAllowShrinking = true,
+                                 size_type aSuffixLength = 0,
+                                 size_type aOldSuffixStart = 0,
+                                 size_type aNewSuffixStart = 0);
 
 protected:
   /**
@@ -950,7 +1257,7 @@ protected:
    * must be less than or equal to the value returned by the most recent
    * StartBulkWrite() call.
    */
-  void NS_FASTCALL FinishBulkWrite(size_type aLength);
+  void NS_FASTCALL FinishBulkWriteImpl(size_type aLength);
 
   /**
    * this function prepares a section of mData to be modified.  if
diff --git a/xpcom/tests/gtest/TestStrings.cpp b/xpcom/tests/gtest/TestStrings.cpp
index 7ed55035c9c7..95f6d6cbe5eb 100644
--- a/xpcom/tests/gtest/TestStrings.cpp
+++ b/xpcom/tests/gtest/TestStrings.cpp
@@ -1326,6 +1326,49 @@ TEST_F(Strings, legacy_set_length_semantics)
   EXPECT_TRUE(s.EqualsASCII(foobar));
 }
 
+TEST_F(Strings, bulk_write)
+{
+  nsresult rv;
+  nsCString s;
+  const char* ptrTwoThousand;
+  {
+    auto handle = s.BulkWrite(500, 0, true, rv);
+    EXPECT_EQ(rv, NS_OK);
+    auto span = handle.AsSpan();
+    for (auto&& c: span) {
+      c = 'a';
+    }
+    mozilla::Unused << handle.RestartBulkWrite(2000, 500, false);
+    span = handle.AsSpan().From(500);
+    for (auto&& c: span) {
+      c = 'b';
+    }
+    ptrTwoThousand = handle.Elements();
+    handle.Finish(1000, true);
+  }
+  EXPECT_EQ(s.Length(), 1000U);
+  EXPECT_NE(s.BeginReading(), ptrTwoThousand);
+  EXPECT_EQ(s.BeginReading()[1000], '\0');
+  for (uint32_t i = 0; i < 500; i++) {
+    EXPECT_EQ(s[i], 'a');
+  }
+  for (uint32_t i = 500; i < 1000; i++) {
+    EXPECT_EQ(s[i], 'b');
+  }
+}
+
+TEST_F(Strings, bulk_write_fail)
+{
+  nsresult rv;
+  nsCString s;
+  {
+    auto handle = s.BulkWrite(500, 0, true, rv);
+    EXPECT_EQ(rv, NS_OK);
+  }
+  EXPECT_EQ(s.Length(), 3U);
+  EXPECT_TRUE(s.Equals(u8"\uFFFD"));
+}
+
 TEST_F(Strings, huge_capacity)
 {
   nsString a, b, c, d, e, f, g, h, i, j, k, l, m, n;