Bug 1388502 - Use a document fragment to populate "all tabs" list. r=johannh

browser/base/content/tabbrowser.xml

@@ -2116,7 +2116,7 @@
           aTab.mCorrespondingMenuitem = menuItem;
           menuItem.tab = aTab;
 
-          this.appendChild(menuItem);
+          return menuItem;
         ]]></body>
       </method>
 
@@ -2203,10 +2203,14 @@
           tabcontainer.addEventListener("TabClose", this);
 
           let tabs = gBrowser.visibleTabs;
+          let fragment = document.createDocumentFragment();
           for (var i = 0; i < tabs.length; i++) {
-            if (!tabs[i].pinned)
-              this._createTabMenuItem(tabs[i]);
+            if (!tabs[i].pinned) {
+              let li = this._createTabMenuItem(tabs[i]);
+              fragment.appendChild(li);
+            }
           }
+          this.appendChild(fragment);
           this._updateTabsVisibilityStatus();
         }
       ]]></handler>