diff --git a/browser/base/content/browser-menubar.inc b/browser/base/content/browser-menubar.inc
index 0ab5e3a68ff6..0b95444aaa3b 100644
--- a/browser/base/content/browser-menubar.inc
+++ b/browser/base/content/browser-menubar.inc
@@ -341,7 +341,7 @@
                 <menuseparator id="sanitizeSeparator"/>
                 <menuitem id="sync-tabs-menuitem"
                           label="&syncTabsMenu3.label;"
-                          oncommand="BrowserOpenSyncTabs();"
+                          oncommand="gSync.openSyncedTabsPanel();"
                           hidden="true"/>
                 <menuitem id="historyRestoreLastSession"
                           label="&historyRestoreLastSession.label;"
diff --git a/browser/base/content/browser.js b/browser/base/content/browser.js
index d160780d4cd5..3d11006b10bc 100644
--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -7299,10 +7299,6 @@ function checkEmptyPageOrigin(browser = gBrowser.selectedBrowser,
   return ssm.isSystemPrincipal(contentPrincipal);
 }
 
-function BrowserOpenSyncTabs() {
-  gSync.openSyncedTabsPanel();
-}
-
 function ReportFalseDeceptiveSite() {
   let docURI = gBrowser.selectedBrowser.documentURI;
   let isPhishingPage =
diff --git a/devtools/client/shared/test/browser_html_tooltip-03.js b/devtools/client/shared/test/browser_html_tooltip-03.js
index f68a5a7e9674..d253d18c5bc0 100644
--- a/devtools/client/shared/test/browser_html_tooltip-03.js
+++ b/devtools/client/shared/test/browser_html_tooltip-03.js
@@ -5,7 +5,7 @@
 "use strict";
 
 /**
- * Test the HTMLTooltip autofocus configuration option.
+ * This is the sanity test for the HTMLTooltip focus
  */
 
 const HTML_NS = "http://www.w3.org/1999/xhtml";
@@ -30,17 +30,11 @@ add_task(async function() {
 });
 
 async function runTests(doc) {
-  await testNoAutoFocus(doc);
-  await testAutoFocus(doc);
-  await testAutoFocusPreservesFocusChange(doc);
-}
-
-async function testNoAutoFocus(doc) {
   await focusNode(doc, "#box4-input");
   ok(doc.activeElement.closest("#box4-input"), "Focus is in the #box4-input");
 
-  info("Test a tooltip without autofocus will not take focus");
-  const tooltip = await createTooltip(doc, false);
+  info("Test a tooltip will not take focus");
+  const tooltip = await createTooltip(doc);
 
   await showTooltip(tooltip, doc.getElementById("box1"));
   ok(doc.activeElement.closest("#box4-input"), "Focus is still in the #box4-input");
@@ -51,50 +45,6 @@ async function testNoAutoFocus(doc) {
   tooltip.destroy();
 }
 
-async function testAutoFocus(doc) {
-  await focusNode(doc, "#box4-input");
-  ok(doc.activeElement.closest("#box4-input"), "Focus is in the #box4-input");
-
-  info("Test autofocus tooltip takes focus when displayed, " +
-    "and restores the focus when hidden");
-  const tooltip = await createTooltip(doc, true);
-
-  await showTooltip(tooltip, doc.getElementById("box1"));
-  ok(doc.activeElement.closest(".tooltip-content"), "Focus is in the tooltip");
-
-  await hideTooltip(tooltip);
-  ok(doc.activeElement.closest("#box4-input"), "Focus is in the #box4-input");
-
-  info("Blur the textbox before moving to the next test to reset the state.");
-  await blurNode(doc, "#box4-input");
-
-  tooltip.destroy();
-}
-
-async function testAutoFocusPreservesFocusChange(doc) {
-  await focusNode(doc, "#box4-input");
-  ok(doc.activeElement.closest("#box4-input"), "Focus is still in the #box3-input");
-
-  info("Test autofocus tooltip takes focus when displayed, " +
-    "but does not try to restore the active element if it is not focused when hidden");
-  const tooltip = await createTooltip(doc, true);
-
-  await showTooltip(tooltip, doc.getElementById("box1"));
-  ok(doc.activeElement.closest(".tooltip-content"), "Focus is in the tooltip");
-
-  info("Move the focus to #box3-input while the tooltip is displayed");
-  await focusNode(doc, "#box3-input");
-  ok(doc.activeElement.closest("#box3-input"), "Focus moved to the #box3-input");
-
-  await hideTooltip(tooltip);
-  ok(doc.activeElement.closest("#box3-input"), "Focus is still in the #box3-input");
-
-  info("Blur the textbox before moving to the next test to reset the state.");
-  await blurNode(doc, "#box3-input");
-
-  tooltip.destroy();
-}
-
 /**
  * Fpcus the node corresponding to the provided selector in the provided document. Returns
  * a promise that will resolve when receiving the focus event on the node.
@@ -118,16 +68,15 @@ function blurNode(doc, selector) {
 }
 
 /**
- * Create an HTMLTooltip instance with the provided autofocus setting.
+ * Create an HTMLTooltip instance.
  *
  * @param {Document} doc
  *        Document in which the tooltip should be created
- * @param {Boolean} autofocus
  * @return {Promise} promise that will resolve the HTMLTooltip instance created when the
  *         tooltip content will be ready.
  */
-function createTooltip(doc, autofocus) {
-  const tooltip = new HTMLTooltip(doc, {autofocus, useXulWrapper});
+function createTooltip(doc) {
+  const tooltip = new HTMLTooltip(doc, {useXulWrapper});
   const div = doc.createElementNS(HTML_NS, "div");
   div.classList.add("tooltip-content");
   div.style.height = "50px";
diff --git a/devtools/client/shared/widgets/tooltip/HTMLTooltip.js b/devtools/client/shared/widgets/tooltip/HTMLTooltip.js
index 35278ed0b8d9..7cffe3830248 100644
--- a/devtools/client/shared/widgets/tooltip/HTMLTooltip.js
+++ b/devtools/client/shared/widgets/tooltip/HTMLTooltip.js
@@ -294,8 +294,6 @@ const getRelativeRect = function(node, relativeTo) {
  *        - {String} type
  *          Display type of the tooltip. Possible values: "normal", "arrow", and
  *          "doorhanger".
- *        - {Boolean} autofocus
- *          Defaults to false. Should the tooltip be focused when opening it.
  *        - {Boolean} consumeOutsideClicks
  *          Defaults to true. The tooltip is closed when clicking outside.
  *          Should this event be stopped and consumed or not.
@@ -307,7 +305,6 @@ function HTMLTooltip(toolboxDoc, {
     id = "",
     className = "",
     type = "normal",
-    autofocus = false,
     consumeOutsideClicks = true,
     useXulWrapper = false,
   } = {}) {
@@ -317,7 +314,6 @@ function HTMLTooltip(toolboxDoc, {
   this.id = id;
   this.className = className;
   this.type = type;
-  this.autofocus = autofocus;
   this.consumeOutsideClicks = consumeOutsideClicks;
   this.useXulWrapper = this._isXUL() && useXulWrapper;
   this.preferredWidth = "auto";
@@ -451,9 +447,6 @@ HTMLTooltip.prototype = {
 
     this.doc.defaultView.clearTimeout(this.attachEventsTimer);
     this.attachEventsTimer = this.doc.defaultView.setTimeout(() => {
-      if (this.autofocus) {
-        this.focus();
-      }
       // Update the top window reference each time in case the host changes.
       this.topWindow = this._getTopWindow();
       this.topWindow.addEventListener("click", this._onClick, true);
diff --git a/xpcom/string/nsTSubstring.cpp b/xpcom/string/nsTSubstring.cpp
index 2c65515763d1..930b98f3e818 100644
--- a/xpcom/string/nsTSubstring.cpp
+++ b/xpcom/string/nsTSubstring.cpp
@@ -92,18 +92,24 @@ nsTSubstring<T>::StartBulkWrite(size_type aCapacity,
   }
 
   // Note! Capacity() returns 0 when the string is immutable.
-  size_type curCapacity = Capacity();
+  const size_type curCapacity = Capacity();
+
+  bool shrinking = false;
 
   // We've established that aCapacity > 0.
   // |curCapacity == 0| means that the buffer is immutable or 0-sized, so we
   // need to allocate a new buffer. We cannot use the existing buffer even
   // though it might be large enough.
 
-  if (!aAllowShrinking && aCapacity <= curCapacity) {
-    char_traits::move(this->mData + aNewSuffixStart,
-                      this->mData + aOldSuffixStart,
-                      aSuffixLength);
-    return curCapacity;
+  if (aCapacity <= curCapacity) {
+    if (aAllowShrinking) {
+      shrinking = true;
+    } else {
+      char_traits::move(this->mData + aNewSuffixStart,
+                        this->mData + aOldSuffixStart,
+                        aSuffixLength);
+      return curCapacity;
+    }
   }
 
   char_type* oldData = this->mData;
@@ -167,6 +173,7 @@ nsTSubstring<T>::StartBulkWrite(size_type aCapacity,
       MOZ_ASSERT(aAllowShrinking, "How come we didn't return earlier?");
       // We're already close enough to the right size.
       newData = oldData;
+      newCapacity = curCapacity;
     } else {
       size_type storageSize = (newCapacity + 1) * sizeof(char_type);
       // Since we allocate only by powers of 2 we always fit into a full mozjemalloc
@@ -174,7 +181,18 @@ nsTSubstring<T>::StartBulkWrite(size_type aCapacity,
       // copying too much.
       nsStringBuffer* newHdr = nsStringBuffer::Alloc(storageSize).take();
       if (!newHdr) {
-        return mozilla::Err(NS_ERROR_OUT_OF_MEMORY); // we are still in a consistent state
+        // 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);
+        }
       }
 
       newData = (char_type*)newHdr->Data();