diff --git a/browser/base/content/browser.js b/browser/base/content/browser.js
index 72dfd3738b71..9f22b5855e57 100644
--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -4563,12 +4563,6 @@ function updateFileMenuUserContextUIVisibility(id) {
     menu.setAttribute("disabled", "true");
   }
 }
-function updateTabMenuUserContextUIVisibility(id) {
-  let menu = document.getElementById(id);
-  // Visibility of Tab menu item can change frequently.
-  menu.hidden = !Services.prefs.getBoolPref("privacy.userContext.enabled", false) ||
-                PrivateBrowsingUtils.isWindowPrivate(window);
-}
 
 /**
  * Updates the User Context UI indicators if the browser is in a non-default context
@@ -4601,44 +4595,6 @@ function updateUserContextUIIndicator() {
   hbox.hidden = false;
 }
 
-/**
- * Fill 'Reopen in Container' menu.
- */
-function createReopenInContainerMenu(event) {
-  let currentid = TabContextMenu.contextTab.getAttribute("usercontextid");
-
-  return createUserContextMenu(event, {
-    isContextMenu: true,
-    excludeUserContextId: currentid,
-  });
-}
-
-/**
- * Reopen the tab in another container.
- */
-function reopenInContainer(event) {
-  let userContextId = parseInt(event.target.getAttribute("data-usercontextid"));
-  let currentTab = TabContextMenu.contextTab;
-  let isSelected = (gBrowser.selectedTab == currentTab);
-  let uri = currentTab.linkedBrowser.currentURI.spec;
-
-  let newTab = gBrowser.addTab(uri, {
-    userContextId,
-    pinned: currentTab.pinned,
-    index: currentTab._tPos + 1,
-  });
-
-  // Carry over some configuration.
-  if (isSelected) {
-    gBrowser.selectedTab = newTab;
-  }
-  if (currentTab.muted) {
-    if (!newTab.muted) {
-      newTab.toggleMuteAudio(currentTab.muteReason);
-    }
-  }
-}
-
 /**
  * Makes the Character Encoding menu enabled or disabled as appropriate.
  * To be called when the View menu or the app menu is opened.
@@ -7843,136 +7799,6 @@ var MenuTouchModeObserver = {
   },
 };
 
-var TabContextMenu = {
-  contextTab: null,
-  _updateToggleMuteMenuItems(aTab, aConditionFn) {
-    ["muted", "soundplaying"].forEach(attr => {
-      if (!aConditionFn || aConditionFn(attr)) {
-        if (aTab.hasAttribute(attr)) {
-          aTab.toggleMuteMenuItem.setAttribute(attr, "true");
-          aTab.toggleMultiSelectMuteMenuItem.setAttribute(attr, "true");
-        } else {
-          aTab.toggleMuteMenuItem.removeAttribute(attr);
-          aTab.toggleMultiSelectMuteMenuItem.removeAttribute(attr);
-        }
-      }
-    });
-  },
-  updateContextMenu: function updateContextMenu(aPopupMenu) {
-    this.contextTab = aPopupMenu.triggerNode.localName == "tab" ?
-                      aPopupMenu.triggerNode : gBrowser.selectedTab;
-    let disabled = gBrowser.tabs.length == 1;
-    let multiselectionContext = this.contextTab.multiselected;
-
-    var menuItems = aPopupMenu.getElementsByAttribute("tbattr", "tabbrowser-multiple");
-    for (let menuItem of menuItems)
-      menuItem.disabled = disabled;
-
-    if (this.contextTab.hasAttribute("customizemode"))
-      document.getElementById("context_openTabInWindow").disabled = true;
-
-    disabled = gBrowser.visibleTabs.length == 1;
-    menuItems = aPopupMenu.getElementsByAttribute("tbattr", "tabbrowser-multiple-visible");
-    for (let menuItem of menuItems)
-      menuItem.disabled = disabled;
-
-    // Session store
-    document.getElementById("context_undoCloseTab").disabled =
-      SessionStore.getClosedTabCount(window) == 0;
-
-    // Only one of Reload_Tab/Reload_Selected_Tabs should be visible.
-    document.getElementById("context_reloadTab").hidden = multiselectionContext;
-    document.getElementById("context_reloadSelectedTabs").hidden = !multiselectionContext;
-
-    // Only one of pin/unpin/multiselect-pin/multiselect-unpin should be visible
-    let contextPinTab = document.getElementById("context_pinTab");
-    contextPinTab.hidden = this.contextTab.pinned || multiselectionContext;
-    let contextUnpinTab = document.getElementById("context_unpinTab");
-    contextUnpinTab.hidden = !this.contextTab.pinned || multiselectionContext;
-    let contextPinSelectedTabs = document.getElementById("context_pinSelectedTabs");
-    contextPinSelectedTabs.hidden = this.contextTab.pinned || !multiselectionContext;
-    let contextUnpinSelectedTabs = document.getElementById("context_unpinSelectedTabs");
-    contextUnpinSelectedTabs.hidden = !this.contextTab.pinned || !multiselectionContext;
-
-    // Disable "Close Tabs to the Right" if there are no tabs
-    // following it.
-    document.getElementById("context_closeTabsToTheEnd").disabled =
-      gBrowser.getTabsToTheEndFrom(this.contextTab).length == 0;
-
-    // Disable "Close other Tabs" if there are no unpinned tabs.
-    let unpinnedTabsToClose = gBrowser.visibleTabs.length - gBrowser._numPinnedTabs;
-    if (!this.contextTab.pinned) {
-      unpinnedTabsToClose--;
-    }
-    document.getElementById("context_closeOtherTabs").disabled = unpinnedTabsToClose < 1;
-
-    // Only one of close_tab/close_selected_tabs should be visible
-    document.getElementById("context_closeTab").hidden = multiselectionContext;
-    document.getElementById("context_closeSelectedTabs").hidden = !multiselectionContext;
-
-    // Hide "Bookmark All Tabs" for a pinned tab.  Update its state if visible.
-    let bookmarkAllTabs = document.getElementById("context_bookmarkAllTabs");
-    bookmarkAllTabs.hidden = this.contextTab.pinned;
-    if (!bookmarkAllTabs.hidden)
-      PlacesCommandHook.updateBookmarkAllTabsCommand();
-
-    let toggleMute = document.getElementById("context_toggleMuteTab");
-    let toggleMultiSelectMute = document.getElementById("context_toggleMuteSelectedTabs");
-
-    // Only one of mute_unmute_tab/mute_unmute_selected_tabs should be visible
-    toggleMute.hidden = multiselectionContext;
-    toggleMultiSelectMute.hidden = !multiselectionContext;
-
-    // Adjust the state of the toggle mute menu item.
-    if (this.contextTab.hasAttribute("activemedia-blocked")) {
-      toggleMute.label = gNavigatorBundle.getString("playTab.label");
-      toggleMute.accessKey = gNavigatorBundle.getString("playTab.accesskey");
-    } else if (this.contextTab.hasAttribute("muted")) {
-      toggleMute.label = gNavigatorBundle.getString("unmuteTab.label");
-      toggleMute.accessKey = gNavigatorBundle.getString("unmuteTab.accesskey");
-    } else {
-      toggleMute.label = gNavigatorBundle.getString("muteTab.label");
-      toggleMute.accessKey = gNavigatorBundle.getString("muteTab.accesskey");
-    }
-
-    // Adjust the state of the toggle mute menu item for multi-selected tabs.
-    if (this.contextTab.hasAttribute("activemedia-blocked")) {
-      toggleMultiSelectMute.label = gNavigatorBundle.getString("playTabs.label");
-      toggleMultiSelectMute.accessKey = gNavigatorBundle.getString("playTabs.accesskey");
-    } else if (this.contextTab.hasAttribute("muted")) {
-      toggleMultiSelectMute.label = gNavigatorBundle.getString("unmuteSelectedTabs.label");
-      toggleMultiSelectMute.accessKey = gNavigatorBundle.getString("unmuteSelectedTabs.accesskey");
-    } else {
-      toggleMultiSelectMute.label = gNavigatorBundle.getString("muteSelectedTabs.label");
-      toggleMultiSelectMute.accessKey = gNavigatorBundle.getString("muteSelectedTabs.accesskey");
-    }
-
-    this.contextTab.toggleMuteMenuItem = toggleMute;
-    this.contextTab.toggleMultiSelectMuteMenuItem = toggleMultiSelectMute;
-    this._updateToggleMuteMenuItems(this.contextTab);
-
-    this.contextTab.addEventListener("TabAttrModified", this);
-    aPopupMenu.addEventListener("popuphiding", this);
-
-    gSync.updateTabContextMenu(aPopupMenu, this.contextTab);
-
-    updateTabMenuUserContextUIVisibility("context_reopenInContainer");
-  },
-  handleEvent(aEvent) {
-    switch (aEvent.type) {
-      case "popuphiding":
-        gBrowser.removeEventListener("TabAttrModified", this);
-        aEvent.target.removeEventListener("popuphiding", this);
-        break;
-      case "TabAttrModified":
-        let tab = aEvent.target;
-        this._updateToggleMuteMenuItems(tab,
-          attr => aEvent.detail.changed.includes(attr));
-        break;
-    }
-  }
-};
-
 // Prompt user to restart the browser in safe mode
 function safeModeRestart() {
   if (Services.appinfo.inSafeMode) {
diff --git a/browser/base/content/browser.xul b/browser/base/content/browser.xul
index 8397e1a6873a..922efe9732c6 100644
--- a/browser/base/content/browser.xul
+++ b/browser/base/content/browser.xul
@@ -114,8 +114,8 @@
             label="&reopenInContainer.label;"
             accesskey="&reopenInContainer.accesskey;"
             hidden="true">
-        <menupopup oncommand="reopenInContainer(event);"
-                   onpopupshowing="return createReopenInContainerMenu(event);" />
+        <menupopup oncommand="TabContextMenu.reopenInContainer(event);"
+                   onpopupshowing="TabContextMenu.createReopenInContainerMenu(event);"/>
       </menu>
       <menuitem id="context_openTabInWindow" label="&moveToNewWindow.label;"
                 accesskey="&moveToNewWindow.accesskey;"
diff --git a/browser/base/content/tabbrowser.js b/browser/base/content/tabbrowser.js
index 9eec8abdd4d1..27ab5ab9f286 100644
--- a/browser/base/content/tabbrowser.js
+++ b/browser/base/content/tabbrowser.js
@@ -4934,3 +4934,162 @@ var TabBarVisibility = {
     TabsInTitlebar.allowedBy("tabs-visible", !collapse);
   }
 };
+
+var TabContextMenu = {
+  contextTab: null,
+  _updateToggleMuteMenuItems(aTab, aConditionFn) {
+    ["muted", "soundplaying"].forEach(attr => {
+      if (!aConditionFn || aConditionFn(attr)) {
+        if (aTab.hasAttribute(attr)) {
+          aTab.toggleMuteMenuItem.setAttribute(attr, "true");
+          aTab.toggleMultiSelectMuteMenuItem.setAttribute(attr, "true");
+        } else {
+          aTab.toggleMuteMenuItem.removeAttribute(attr);
+          aTab.toggleMultiSelectMuteMenuItem.removeAttribute(attr);
+        }
+      }
+    });
+  },
+  updateContextMenu(aPopupMenu) {
+    this.contextTab = aPopupMenu.triggerNode.localName == "tab" ?
+                      aPopupMenu.triggerNode : gBrowser.selectedTab;
+    let disabled = gBrowser.tabs.length == 1;
+    let multiselectionContext = this.contextTab.multiselected;
+
+    var menuItems = aPopupMenu.getElementsByAttribute("tbattr", "tabbrowser-multiple");
+    for (let menuItem of menuItems) {
+      menuItem.disabled = disabled;
+    }
+
+    if (this.contextTab.hasAttribute("customizemode")) {
+      document.getElementById("context_openTabInWindow").disabled = true;
+    }
+
+    disabled = gBrowser.visibleTabs.length == 1;
+    menuItems = aPopupMenu.getElementsByAttribute("tbattr", "tabbrowser-multiple-visible");
+    for (let menuItem of menuItems) {
+      menuItem.disabled = disabled;
+    }
+
+    // Session store
+    document.getElementById("context_undoCloseTab").disabled =
+      SessionStore.getClosedTabCount(window) == 0;
+
+    // Only one of Reload_Tab/Reload_Selected_Tabs should be visible.
+    document.getElementById("context_reloadTab").hidden = multiselectionContext;
+    document.getElementById("context_reloadSelectedTabs").hidden = !multiselectionContext;
+
+    // Only one of pin/unpin/multiselect-pin/multiselect-unpin should be visible
+    let contextPinTab = document.getElementById("context_pinTab");
+    contextPinTab.hidden = this.contextTab.pinned || multiselectionContext;
+    let contextUnpinTab = document.getElementById("context_unpinTab");
+    contextUnpinTab.hidden = !this.contextTab.pinned || multiselectionContext;
+    let contextPinSelectedTabs = document.getElementById("context_pinSelectedTabs");
+    contextPinSelectedTabs.hidden = this.contextTab.pinned || !multiselectionContext;
+    let contextUnpinSelectedTabs = document.getElementById("context_unpinSelectedTabs");
+    contextUnpinSelectedTabs.hidden = !this.contextTab.pinned || !multiselectionContext;
+
+    // Disable "Close Tabs to the Right" if there are no tabs
+    // following it.
+    document.getElementById("context_closeTabsToTheEnd").disabled =
+      gBrowser.getTabsToTheEndFrom(this.contextTab).length == 0;
+
+    // Disable "Close other Tabs" if there are no unpinned tabs.
+    let unpinnedTabsToClose = gBrowser.visibleTabs.length - gBrowser._numPinnedTabs;
+    if (!this.contextTab.pinned) {
+      unpinnedTabsToClose--;
+    }
+    document.getElementById("context_closeOtherTabs").disabled = unpinnedTabsToClose < 1;
+
+    // Only one of close_tab/close_selected_tabs should be visible
+    document.getElementById("context_closeTab").hidden = multiselectionContext;
+    document.getElementById("context_closeSelectedTabs").hidden = !multiselectionContext;
+
+    // Hide "Bookmark All Tabs" for a pinned tab.  Update its state if visible.
+    let bookmarkAllTabs = document.getElementById("context_bookmarkAllTabs");
+    bookmarkAllTabs.hidden = this.contextTab.pinned;
+    if (!bookmarkAllTabs.hidden) {
+      PlacesCommandHook.updateBookmarkAllTabsCommand();
+    }
+
+    let toggleMute = document.getElementById("context_toggleMuteTab");
+    let toggleMultiSelectMute = document.getElementById("context_toggleMuteSelectedTabs");
+
+    // Only one of mute_unmute_tab/mute_unmute_selected_tabs should be visible
+    toggleMute.hidden = multiselectionContext;
+    toggleMultiSelectMute.hidden = !multiselectionContext;
+
+    // Adjust the state of the toggle mute menu item.
+    if (this.contextTab.hasAttribute("activemedia-blocked")) {
+      toggleMute.label = gNavigatorBundle.getString("playTab.label");
+      toggleMute.accessKey = gNavigatorBundle.getString("playTab.accesskey");
+    } else if (this.contextTab.hasAttribute("muted")) {
+      toggleMute.label = gNavigatorBundle.getString("unmuteTab.label");
+      toggleMute.accessKey = gNavigatorBundle.getString("unmuteTab.accesskey");
+    } else {
+      toggleMute.label = gNavigatorBundle.getString("muteTab.label");
+      toggleMute.accessKey = gNavigatorBundle.getString("muteTab.accesskey");
+    }
+
+    // Adjust the state of the toggle mute menu item for multi-selected tabs.
+    if (this.contextTab.hasAttribute("activemedia-blocked")) {
+      toggleMultiSelectMute.label = gNavigatorBundle.getString("playTabs.label");
+      toggleMultiSelectMute.accessKey = gNavigatorBundle.getString("playTabs.accesskey");
+    } else if (this.contextTab.hasAttribute("muted")) {
+      toggleMultiSelectMute.label = gNavigatorBundle.getString("unmuteSelectedTabs.label");
+      toggleMultiSelectMute.accessKey = gNavigatorBundle.getString("unmuteSelectedTabs.accesskey");
+    } else {
+      toggleMultiSelectMute.label = gNavigatorBundle.getString("muteSelectedTabs.label");
+      toggleMultiSelectMute.accessKey = gNavigatorBundle.getString("muteSelectedTabs.accesskey");
+    }
+
+    this.contextTab.toggleMuteMenuItem = toggleMute;
+    this.contextTab.toggleMultiSelectMuteMenuItem = toggleMultiSelectMute;
+    this._updateToggleMuteMenuItems(this.contextTab);
+
+    this.contextTab.addEventListener("TabAttrModified", this);
+    aPopupMenu.addEventListener("popuphiding", this);
+
+    gSync.updateTabContextMenu(aPopupMenu, this.contextTab);
+
+    document.getElementById("context_reopenInContainer").hidden =
+      !Services.prefs.getBoolPref("privacy.userContext.enabled", false) ||
+      PrivateBrowsingUtils.isWindowPrivate(window);
+  },
+  handleEvent(aEvent) {
+    switch (aEvent.type) {
+      case "popuphiding":
+        gBrowser.removeEventListener("TabAttrModified", this);
+        aEvent.target.removeEventListener("popuphiding", this);
+        break;
+      case "TabAttrModified":
+        let tab = aEvent.target;
+        this._updateToggleMuteMenuItems(tab,
+          attr => aEvent.detail.changed.includes(attr));
+        break;
+    }
+  },
+  createReopenInContainerMenu(event) {
+    createUserContextMenu(event, {
+      isContextMenu: true,
+      excludeUserContextId: this.contextTab.getAttribute("usercontextid"),
+    });
+  },
+  reopenInContainer(event) {
+    let newTab = gBrowser.addTab(this.contextTab.linkedBrowser.currentURI.spec, {
+      userContextId: parseInt(event.target.getAttribute("data-usercontextid")),
+      pinned: this.contextTab.pinned,
+      index: this.contextTab._tPos + 1,
+    });
+
+    if (gBrowser.selectedTab == this.contextTab) {
+      gBrowser.selectedTab = newTab;
+    }
+    if (this.contextTab.muted) {
+      if (!newTab.muted) {
+        newTab.toggleMuteAudio(this.contextTab.muteReason);
+      }
+    }
+  }
+};
+
diff --git a/browser/base/content/tabbrowser.xml b/browser/base/content/tabbrowser.xml
index 158a47f18728..5e42159ca9f6 100644
--- a/browser/base/content/tabbrowser.xml
+++ b/browser/base/content/tabbrowser.xml
@@ -56,10 +56,8 @@
         // Ignore overflow events:
         // - from nested scrollable elements
         // - for vertical orientation
-        // - when the window is tiny initially
         if (event.originalTarget != this._scrollbox ||
-            event.detail == 0 ||
-            window.outerWidth <= 1) {
+            event.detail == 0) {
           return;
         }
 
diff --git a/browser/base/content/test/sync/browser_contextmenu_sendtab.js b/browser/base/content/test/sync/browser_contextmenu_sendtab.js
index e2839dc6cc6c..09e3866ca9ff 100644
--- a/browser/base/content/test/sync/browser_contextmenu_sendtab.js
+++ b/browser/base/content/test/sync/browser_contextmenu_sendtab.js
@@ -18,7 +18,7 @@ function updateTabContextMenu(tab) {
   var evt = new Event("");
   tab.dispatchEvent(evt);
   menu.openPopup(tab, "end_after", 0, 0, true, false, evt);
-  is(TabContextMenu.contextTab, tab, "TabContextMenu context is the expected tab");
+  is(window.TabContextMenu.contextTab, tab, "TabContextMenu context is the expected tab");
   menu.hidePopup();
 }
 
diff --git a/browser/base/content/test/tabs/head.js b/browser/base/content/test/tabs/head.js
index 8858dc9d5d60..8e4fd7d0509c 100644
--- a/browser/base/content/test/tabs/head.js
+++ b/browser/base/content/test/tabs/head.js
@@ -5,7 +5,7 @@ function updateTabContextMenu(tab) {
   var evt = new Event("");
   tab.dispatchEvent(evt);
   menu.openPopup(tab, "end_after", 0, 0, true, false, evt);
-  is(TabContextMenu.contextTab, tab, "TabContextMenu context is the expected tab");
+  is(window.TabContextMenu.contextTab, tab, "TabContextMenu context is the expected tab");
   menu.hidePopup();
 }
 
diff --git a/js/xpconnect/tests/unit/head_watchdog.js b/js/xpconnect/tests/unit/head_watchdog.js
index 90abfb133a47..274a2fabe9a9 100644
--- a/js/xpconnect/tests/unit/head_watchdog.js
+++ b/js/xpconnect/tests/unit/head_watchdog.js
@@ -65,29 +65,33 @@ function executeSoon(fn) {
 // We wait 3 seconds, just to be safe.
 //
 
-function checkWatchdog(expectInterrupt, continuation) {
+function checkWatchdog(expectInterrupt) {
   var oldTimeout = setScriptTimeout(1);
   var lastWatchdogWakeup = Cu.getWatchdogTimestamp("WatchdogWakeup");
-  setInterruptCallback(function() {
-    // If the watchdog didn't actually trigger the operation callback, ignore
-    // this call. This allows us to test the actual watchdog behavior without
-    // interference from other sites where we trigger the operation callback.
-    if (lastWatchdogWakeup == Cu.getWatchdogTimestamp("WatchdogWakeup")) {
-      return true;
-    }
-    Assert.ok(expectInterrupt);
-    setInterruptCallback(undefined);
-    setScriptTimeout(oldTimeout);
-    // Schedule our continuation before we kill this script.
-    executeSoon(continuation);
-    return false;
-  });
-  executeSoon(function() {
-    busyWait(3000);
-    Assert.ok(!expectInterrupt);
-    setInterruptCallback(undefined);
-    setScriptTimeout(oldTimeout);
-    continuation();
+
+  return new Promise(resolve => {
+    setInterruptCallback(function() {
+      // If the watchdog didn't actually trigger the operation callback, ignore
+      // this call. This allows us to test the actual watchdog behavior without
+      // interference from other sites where we trigger the operation callback.
+      if (lastWatchdogWakeup == Cu.getWatchdogTimestamp("WatchdogWakeup")) {
+        return true;
+      }
+      Assert.ok(expectInterrupt, "Interrupt callback fired");
+      setInterruptCallback(undefined);
+      setScriptTimeout(oldTimeout);
+      // Schedule the promise for resolution before we kill this script.
+      executeSoon(resolve);
+      return false;
+    });
+
+    executeSoon(function() {
+      busyWait(3000);
+      Assert.ok(!expectInterrupt, "Interrupt callback didn't fire");
+      setInterruptCallback(undefined);
+      setScriptTimeout(oldTimeout);
+      resolve();
+    });
   });
 }
 
diff --git a/js/xpconnect/tests/unit/test_watchdog_default.js b/js/xpconnect/tests/unit/test_watchdog_default.js
index 75e8f0e7632b..4634184f3c40 100644
--- a/js/xpconnect/tests/unit/test_watchdog_default.js
+++ b/js/xpconnect/tests/unit/test_watchdog_default.js
@@ -2,8 +2,8 @@
  * 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/. */
 
-async function testBody() {
+function testBody() {
   // Check that we properly implement whatever behavior is specified by the
   // default profile for this configuration.
-  await checkWatchdog(isWatchdogEnabled());
+  return checkWatchdog(isWatchdogEnabled());
 }
diff --git a/js/xpconnect/tests/unit/test_watchdog_disable.js b/js/xpconnect/tests/unit/test_watchdog_disable.js
index 45837dabaf5b..926edf2ffa1f 100644
--- a/js/xpconnect/tests/unit/test_watchdog_disable.js
+++ b/js/xpconnect/tests/unit/test_watchdog_disable.js
@@ -2,7 +2,7 @@
  * 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/. */
 
-async function testBody() {
+function testBody() {
   setWatchdogEnabled(false);
-  await checkWatchdog(false);
+  return checkWatchdog(false);
 }
diff --git a/js/xpconnect/tests/unit/test_watchdog_enable.js b/js/xpconnect/tests/unit/test_watchdog_enable.js
index 234e7d76a49c..f39757dfae95 100644
--- a/js/xpconnect/tests/unit/test_watchdog_enable.js
+++ b/js/xpconnect/tests/unit/test_watchdog_enable.js
@@ -2,7 +2,7 @@
  * 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/. */
 
-async function testBody() {
+function testBody() {
   setWatchdogEnabled(true);
-  await checkWatchdog(true);
+  return checkWatchdog(true);
 }
diff --git a/js/xpconnect/tests/unit/test_watchdog_hibernate.js b/js/xpconnect/tests/unit/test_watchdog_hibernate.js
index 44e141c8e056..1207e6ff5c98 100644
--- a/js/xpconnect/tests/unit/test_watchdog_hibernate.js
+++ b/js/xpconnect/tests/unit/test_watchdog_hibernate.js
@@ -15,8 +15,8 @@ async function testBody() {
   do_log_info("now: " + now / 1000000);
   do_log_info("startHibernation: " + startHibernation / 1000000);
   do_log_info("stopHibernation: " + stopHibernation / 1000000);
-  Assert.ok(startHibernation < now);
-  Assert.ok(stopHibernation < now);
+  Assert.ok(startHibernation < now, "startHibernation ok");
+  Assert.ok(stopHibernation < now, "stopHibernation ok");
 
   // When the watchdog runs, it hibernates if there's been no activity for the
   // last 2 seconds, otherwise it sleeps for 1 second. As such, given perfect
@@ -44,8 +44,8 @@ async function testBody() {
   // making sure this behavior is roughly as expected on the macro scale,
   // so we add a 1 second fuzz factor here.
   const FUZZ_FACTOR = 1 * 1000 * 1000;
-  Assert.ok(stateChange > now + 10*1000*1000 - FUZZ_FACTOR);
-  Assert.ok(startHibernation > now + 2*1000*1000 - FUZZ_FACTOR);
-  Assert.ok(startHibernation < now + 5*1000*1000 + FUZZ_FACTOR);
-  Assert.ok(stopHibernation > now + 10*1000*1000 - FUZZ_FACTOR);
+  Assert.ok(stateChange > now + 10*1000*1000 - FUZZ_FACTOR, "stateChange ok");
+  Assert.ok(startHibernation > now + 2*1000*1000 - FUZZ_FACTOR, "startHibernation ok");
+  Assert.ok(startHibernation < now + 5*1000*1000 + FUZZ_FACTOR, "startHibernation ok");
+  Assert.ok(stopHibernation > now + 10*1000*1000 - FUZZ_FACTOR, "stopHibernation ok");
 }
diff --git a/js/xpconnect/tests/unit/test_watchdog_toggle.js b/js/xpconnect/tests/unit/test_watchdog_toggle.js
index 1b2c90df9d03..6f43a8b876b9 100644
--- a/js/xpconnect/tests/unit/test_watchdog_toggle.js
+++ b/js/xpconnect/tests/unit/test_watchdog_toggle.js
@@ -2,9 +2,9 @@
  * 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/. */
 
-async function testBody() {
+function testBody() {
   var defaultBehavior = isWatchdogEnabled();
   setWatchdogEnabled(!defaultBehavior);
   setWatchdogEnabled(defaultBehavior);
-  await checkWatchdog(defaultBehavior);
+  return checkWatchdog(defaultBehavior);
 }
diff --git a/layout/painting/nsDisplayList.cpp b/layout/painting/nsDisplayList.cpp
index f22dde175fd5..53af15c8b996 100644
--- a/layout/painting/nsDisplayList.cpp
+++ b/layout/painting/nsDisplayList.cpp
@@ -9838,6 +9838,8 @@ PaintTelemetry::AutoRecordPaint::~AutoRecordPaint()
     recordSmall(NS_LITERAL_CSTRING("fr"), frMs);
     recordSmall(NS_LITERAL_CSTRING("r"), rMs);
   }
+
+  Telemetry::Accumulate(Telemetry::PAINT_BUILD_LAYERS_TIME, flbMs);
 }
 
 PaintTelemetry::AutoRecord::AutoRecord(Metric aMetric)
diff --git a/toolkit/components/telemetry/Histograms.json b/toolkit/components/telemetry/Histograms.json
index c91d54ad2094..924a7883ac98 100644
--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -3381,6 +3381,16 @@
     "high": 1000,
     "n_buckets": 50
   },
+  "PAINT_BUILD_LAYERS_TIME" : {
+    "record_in_processes": ["content"],
+    "alert_emails": ["gfx-telemetry-alerts@mozilla.com","mwoodrow@mozilla.com"],
+    "bug_numbers": [1473908],
+    "expires_in_version": "never",
+    "description": "Time spent in building layers in milliseconds",
+    "kind": "exponential",
+    "high": 1000,
+    "n_buckets": 50
+  },
   "PAINT_RASTERIZE_TIME" : {
     "record_in_processes": ["main", "content"],
     "expires_in_version": "never",
diff --git a/toolkit/content/widgets/scrollbox.xml b/toolkit/content/widgets/scrollbox.xml
index 8dbca4e97731..ac669b6eaee7 100644
--- a/toolkit/content/widgets/scrollbox.xml
+++ b/toolkit/content/widgets/scrollbox.xml
@@ -570,9 +570,7 @@
       <handler event="overflow" phase="capturing"><![CDATA[
         // Ignore overflow events:
         // - from nested scrollable elements
-        // - when the window is tiny initially
-        if (event.target != this ||
-            window.outerWidth <= 1) {
+        if (event.target != this) {
           return;
         }