--- a/browser/base/content/tabbrowser.xml
+++ b/browser/base/content/tabbrowser.xml
@@ -841,18 +841,22 @@
                 document.commandDispatcher.focusedElement.parentNode ==
                 this.mCurrentTab.parentNode) {
               // The focus is on a tab in the same tab panel
               return;  // If focus was on a tab, switching tabs focuses the new tab
             }
 
             var whatToFocus = window.content;
 
-            // Focus the previously focused element or window
-            if (newBrowser.focusedElement) {
+            // Focus the previously focused element or window, but make sure
+            // the focused element is still part of the document
+            let focusedElem = newBrowser.focusedElement;
+            if (focusedElem && focusedElem.ownerDocument &&
+                !(focusedElem.ownerDocument.compareDocumentPosition(focusedElem) &
+                  Node.DOCUMENT_POSITION_DISCONNECTED)) {
               if (newBrowser.focusedElement.parentNode !=
                   this.mCurrentTab.parentNode) {
                 // Focus the remembered element unless it's in the current tab panel
                 whatToFocus = newBrowser.focusedElement;
               }
             }
             else if (newBrowser.focusedWindow) {
               whatToFocus = newBrowser.focusedWindow;

--- a/browser/base/content/test/Makefile.in
+++ b/browser/base/content/test/Makefile.in
@@ -53,15 +53,16 @@ include $(topsrcdir)/config/rules.mk
 _BROWSER_FILES = browser_bug321000.js \
                  browser_bug405137.js \
                  browser_bug409481.js \
                  browser_autodiscovery.js \
                  browser_bug420160.js \
                  autodiscovery.html \
                  moz.png \
                  browser_getshortcutoruri.js \
+                 browser_bug427559.js \
     $(NULL)
 
 libs:: $(_TEST_FILES)
 	$(INSTALL) $(foreach f,$^,"$f") $(DEPTH)/_tests/testing/mochitest/tests/$(relativesrcdir)
 
 libs::	$(_BROWSER_FILES)
 	$(INSTALL) $(foreach f,$^,"$f") $(DEPTH)/_tests/testing/mochitest/browser/$(relativesrcdir)

new file mode 100644
--- /dev/null
+++ b/browser/base/content/test/browser_bug427559.js
@@ -0,0 +1,72 @@
+/* ***** BEGIN LICENSE BLOCK *****
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Original Code is Firefox Browser Test Code.
+ *
+ * The Initial Developer of the Original Code is
+ * Edward Lee <edward.lee@engineering.uiuc.edu>.
+ * Portions created by the Initial Developer are Copyright (C) 2008
+ * the Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s):
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+/*
+ * Test bug 427559 to make sure focused elements that are no longer on the page
+ * will have focus transferred to the window when changing tabs back to that
+ * tab with the now-gone element.
+ */
+
+// Default focus on a button and have it kill itself on blur
+let testPage = 'data:text/html,<body><button onblur="this.parentNode.removeChild(this);"><script>document.body.firstChild.focus();</script></body>';
+
+function test() {
+  waitForExplicitFinish();
+
+  // Prepare the test tab
+  let testTab = gBrowser.addTab();
+  gBrowser.selectedTab = testTab;
+  let testBrowser = gBrowser.getBrowserForTab(testTab);
+
+  testBrowser.addEventListener("load", function() {
+    // The test page loaded, so open an empty tab, select it, then restore
+    // the test tab. This causes the test page's focused element to be removed
+    // from its document.
+    let emptyTab = gBrowser.addTab();
+    gBrowser.selectedTab = emptyTab;
+    gBrowser.removeCurrentTab();
+    gBrowser.selectedTab = testTab;
+
+    // Make sure focus is given to the window because the element is now gone
+    is(document.commandDispatcher.focusedWindow, window.content,
+       "content window is focused");
+    gBrowser.removeCurrentTab();
+    finish();
+  }, true);
+
+  // Start the test by loading the test page
+  testBrowser.contentWindow.location = testPage;
+}