diff --git a/mozilla/browser/base/content/browser.js b/mozilla/browser/base/content/browser.js
index a7afc202e81..d1a6273a158 100644
--- a/mozilla/browser/base/content/browser.js
+++ b/mozilla/browser/base/content/browser.js
@@ -1124,6 +1124,9 @@ function delayedStartup()
       }
     }
   }
+
+  // browser-specific tab augmentation
+  AugmentTabs.init();
 }
 
 function BrowserShutdown()
@@ -6642,3 +6645,57 @@ window.controllers.appendController(BrowserController);
 #include ../../../toolkit/content/debug.js
 
 #endif
+
+/**
+ * This object is for augmenting tabs
+ */
+var AugmentTabs = {
+  /**
+   * Called in delayedStartup
+   */
+  init: function at_init() {
+    // add the tab context menu for undo-close-tab (bz254021)
+    var ssEnabled = true;
+    var prefBranch = Cc["@mozilla.org/preferences-service;1"].
+                     getService(Ci.nsIPrefBranch);
+    try {
+      ssEnabled = prefBranch.getBoolPref("browser.sessionstore.enabled");
+    } catch (ex) {}
+
+    if (ssEnabled)
+      this._addUndoCloseTabContextMenu();
+  },
+
+  /**
+   * Add undo-close-tab to tab context menu
+   */
+  _addUndoCloseTabContextMenu: function at_addUndoCloseTabContextMenu() {
+    // get tab context menu
+    var tabbrowser = getBrowser();
+    var tabMenu = document.getAnonymousElementByAttribute(tabbrowser,"anonid","tabContextMenu");
+
+    // get strings 
+    var menuLabel = gNavigatorBundle.getString("tabContext.undoCloseTab");
+    var menuAccessKey = gNavigatorBundle.getString("tabContext.undoCloseTabAccessKey");
+
+    // create new menu item
+    var undoCloseTabItem = document.createElement("menuitem");
+    undoCloseTabItem.setAttribute("label", menuLabel);
+    undoCloseTabItem.setAttribute("accesskey", menuAccessKey);
+    undoCloseTabItem.addEventListener("command", this.undoCloseTab, false);
+
+    // add to tab context menu
+    var insertPos = tabMenu.lastChild.previousSibling;
+    tabMenu.insertBefore(undoCloseTabItem, insertPos);
+  },
+
+  /**
+   * Re-open the most-recently-closed tab
+   */
+  undoCloseTab: function at_undoCloseTab() {
+    // get session-store service
+    var ss = Cc["@mozilla.org/browser/sessionstore;1"].
+             getService(Ci.nsISessionStore);
+    ss.undoCloseTab(window, 0);
+  }
+};
diff --git a/mozilla/browser/components/sessionstore/nsISessionStore.idl b/mozilla/browser/components/sessionstore/nsISessionStore.idl
index 8343eb127fe..384a9b2c3b9 100644
--- a/mozilla/browser/components/sessionstore/nsISessionStore.idl
+++ b/mozilla/browser/components/sessionstore/nsISessionStore.idl
@@ -53,4 +53,12 @@ interface nsISessionStore : nsISupports
    * Initialize the service
    */
   void init(in nsIDOMWindow aWindow);
+
+  /**
+   * @param aWindow
+   *          The window to reopen a closed tab in.
+   * @param aIndex
+   *          Indicates the window to be restored (FIFO ordered).
+   */
+  void undoCloseTab(in nsIDOMWindow aWindow, in unsigned long aIndex);
 };
diff --git a/mozilla/browser/components/sessionstore/src/nsSessionStore.js b/mozilla/browser/components/sessionstore/src/nsSessionStore.js
index 3429e3eeeb7..357bd717f6d 100644
--- a/mozilla/browser/components/sessionstore/src/nsSessionStore.js
+++ b/mozilla/browser/components/sessionstore/src/nsSessionStore.js
@@ -422,7 +422,7 @@ SessionStoreService.prototype = {
     tabpanels.addEventListener("select", function(aEvent) {
       _this.onTabSelect(aEvent.currentTarget.ownerDocument.defaultView, aEvent.currentTarget);
       }, false);
-    tabbrowser.addEventListener("TabClose", function(aEvent) {
+    tabbrowser.addEventListener("DOMNodeRemoved", function(aEvent) {
       _this.onTabClose(aEvent.currentTarget.ownerDocument.defaultView, aEvent.originalTarget);
       }, false);
   },
@@ -539,12 +539,17 @@ SessionStoreService.prototype = {
     this._saveWindowHistory(aWindow);
     this._updateTextAndScrollData(aWindow);
     
-    this._windows[aWindow.__SSi]._closedTabs.unshift({
-      state: this._windows[aWindow.__SSi].Tab[aTab._tPos],
-      title: aTab.getAttribute("label"),
-      pos: aTab._tPos
-    });
-    this._windows[aWindow.__SSi]._closedTabs.splice(this._getPref("sessionstore.max_tabs_undo", DEFAULT_MAX_TABS_UNDO));
+    // DOMNodeRemoved is received *twice* after closing a tab, only take the first
+    var tabState = this._windows[aWindow.__SSi].Tab[aTab._tPos];
+    if (tabState) {
+      this._windows[aWindow.__SSi]._closedTabs.unshift({
+        state: tabState,
+        title: aTab.getAttribute("label"),
+        pos: aTab._tPos
+      });
+      var maxTabsUndo = this._getPref("sessionstore.max_tabs_undo", DEFAULT_MAX_TABS_UNDO);
+      this._windows[aWindow.__SSi]._closedTabs.splice(maxTabsUndo);
+    }
   },
 
   /**
@@ -685,22 +690,30 @@ SessionStoreService.prototype = {
     this._windows[aWindow.__SSi]._closedTabs = IniObjectSerializer.decode(aData);
   },
 
-  undoCloseTab: function sss_undoCloseWindow(aWindow, aIx) {
-    var tabs = this._windows[aWindow.__SSi]._closedTabs;
+  undoCloseTab: function sss_undoCloseTab(aWindow, aIndex) {
+    var closedTabs = this._windows[aWindow.__SSi]._closedTabs;
+
+    // default to the most-recently closed tab
+    aIndex = aIndex || 0;
     
-    if (aIx in tabs) {
+    if (aIndex in closedTabs) {
       var browser = aWindow.getBrowser();
-      var tabData = tabs.splice(aIx, 1);
-      tabData._tab = browser.addTab();
+
+      // fetch the data of closed tab, while removing it from the array
+      var closedTab = closedTabs.splice(aIndex, 1).shift();
+      var closedTabState = closedTab.state;
+
+      // create a new tab
+      closedTabState._tab = browser.addTab();
       
       // restore the tab's position
-      browser.moveTabTo(tabData._tab, tabData[0].pos);
+      browser.moveTabTo(closedTabState._tab, closedTab.pos);
 
-      // restore the tab's state
-      aWindow.setTimeout(this.restoreHistory_proxy, 0, tabData, 1, 0, 0);
+      // restore tab content
+      this.restoreHistoryPrecursor(aWindow, [closedTabState], 1, 0, 0);
     }
     else {
-      Components.returnCode = -1; //zeniko: or should we rather fail silently?
+      Components.returnCode = Cr.NS_ERROR_INVALID_ARG;
     }
   },
 
@@ -1195,11 +1208,8 @@ SessionStoreService.prototype = {
       }
     }
     
-    var restoreHistoryFunc = function(self) {
-      self.restoreHistory_proxy(aWindow, winData.Tab, (aOverwriteTabs ?
+    this.restoreHistoryPrecursor(aWindow, winData.Tab, (aOverwriteTabs ?
       (parseInt(winData.selected) || 1) : 0), 0, 0);
-    };
-    aWindow.setTimeout(restoreHistoryFunc, 0, this);
   },
 
   /**
@@ -1213,7 +1223,7 @@ SessionStoreService.prototype = {
    * @param aCount
    *        Counter for number of times delaying b/c browser or history aren't ready
    */
-  restoreHistory_proxy: function sss_restoreHistory_proxy(aWindow, aTabs, aSelectTab, aIx, aCount) {
+  restoreHistoryPrecursor: function sss_restoreHistoryPrecursor(aWindow, aTabs, aSelectTab, aIx, aCount) {
     var tabbrowser = aWindow.getBrowser();
     
     // make sure that all browsers and their histories are available
@@ -1227,7 +1237,7 @@ SessionStoreService.prototype = {
       catch (ex) { // in case browser or history aren't ready yet 
         if (aCount < 10) {
           var restoreHistoryFunc = function(self) {
-            self.restoreHistory_proxy(aWindow, aTabs, aSelectTab, aIx, aCount + 1);
+            self.restoreHistoryPrecursor(aWindow, aTabs, aSelectTab, aIx, aCount + 1);
           }
           aWindow.setTimeout(restoreHistoryFunc, 100, this);
           return;
diff --git a/mozilla/browser/locales/en-US/chrome/browser/browser.properties b/mozilla/browser/locales/en-US/chrome/browser/browser.properties
index d533ef7af2f..07a805dcb07 100644
--- a/mozilla/browser/locales/en-US/chrome/browser/browser.properties
+++ b/mozilla/browser/locales/en-US/chrome/browser/browser.properties
@@ -119,3 +119,7 @@ feedHasFeeds=Add Live Bookmark...
 feedNoFeeds=Page has no feeds
 feedShowFeedNew=Subscribe to '%S'...
 feedHasFeedsNew=Subscribe to this page...
+
+# tab context menu additions
+tabContext.undoCloseTab=Undo Close Tab
+tabContext.undoCloseTabAccessKey=U