--- a/widget/src/cocoa/nsMenuGroupOwnerX.mm
+++ b/widget/src/cocoa/nsMenuGroupOwnerX.mm
@@ -159,21 +159,25 @@ void nsMenuGroupOwnerX::AttributeChanged
 
 
 void nsMenuGroupOwnerX::ContentRemoved(nsIDocument * aDocument,
                                        nsIContent * aContainer,
                                        nsIContent * aChild,
                                        PRInt32 aIndexInContainer,
                                        nsIContent * aPreviousSibling)
 {
+  if (!aContainer) {
+    return;
+  }
+
   nsCOMPtr<nsIMutationObserver> kungFuDeathGrip(this);
   nsChangeObserver* obs = LookupContentChangeObserver(aContainer);
   if (obs)
     obs->ObserveContentRemoved(aDocument, aChild, aIndexInContainer);
-  else if (aContainer && (aContainer != mContent)) {
+  else if (aContainer != mContent) {
     // We do a lookup on the parent container in case things were removed
     // under a "menupopup" item. That is basically a wrapper for the contents
     // of a "menu" node.
     nsCOMPtr<nsIContent> parent = aContainer->GetParent();
     if (parent) {
       obs = LookupContentChangeObserver(parent);
       if (obs)
         obs->ObserveContentRemoved(aDocument, aChild, aIndexInContainer);
@@ -182,16 +186,20 @@ void nsMenuGroupOwnerX::ContentRemoved(n
 }
 
 
 void nsMenuGroupOwnerX::ContentInserted(nsIDocument * aDocument,
                                         nsIContent * aContainer,
                                         nsIContent * aChild,
                                         PRInt32 aIndexInContainer)
 {
+  if (!aContainer) {
+    return;
+  }
+
   nsCOMPtr<nsIMutationObserver> kungFuDeathGrip(this);
   nsChangeObserver* obs = LookupContentChangeObserver(aContainer);
   if (obs)
     obs->ObserveContentInserted(aDocument, aChild, aIndexInContainer);
   else if (aContainer != mContent) {
     // We do a lookup on the parent container in case things were removed
     // under a "menupopup" item. That is basically a wrapper for the contents
     // of a "menu" node.

--- a/widget/tests/Makefile.in
+++ b/widget/tests/Makefile.in
@@ -87,16 +87,18 @@ ifeq ($(MOZ_WIDGET_TOOLKIT),cocoa)
                test_bug428405.xul \
                test_bug466599.xul \
                test_bug485118.xul \
                test_bug522217.xul \
                window_bug522217.xul \
                test_platform_colors.xul \
                test_standalone_native_menu.xul \
                standalone_native_menu_window.xul \
+               test_bug586713.xul \
+               bug586713_window.xul \
                $(NULL)
 endif
 
 ifeq ($(MOZ_WIDGET_TOOLKIT),windows)
 ifneq ($(OS_ARCH), WINCE)
 _CHROME_FILES  += taskbar_previews.xul \
 		window_state_windows.xul \
 		taskbar_progress.xul \

new file mode 100644
--- /dev/null
+++ b/widget/tests/bug586713_window.xul
@@ -0,0 +1,83 @@
+<?xml version="1.0"?>
+
+<!-- ***** 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 Native Menus Test code
+   -
+   - The Initial Developer of the Original Code is
+   - Mozilla Corporation.
+   - Portions created by the Initial Developer are Copyright (C) 2010
+   - the Initial Developer. All Rights Reserved.
+   -
+   - Contributor(s):
+   -   Josh Aas <josh@mozilla.com>
+   -
+   - 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 ***** -->
+
+<?xml-stylesheet href="chrome://global/skin" type="text/css"?>
+
+<window id="bug586713_window"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        width="300"
+        height="300"
+        onload="onLoad();"
+        title="Bug 586713 Test">
+
+  <menubar id="nativemenubar">
+    <menu id="foo" label="Foo">
+      <menupopup>
+        <menuitem label="FooItem0"/>
+      </menupopup>
+    </menu>
+  </menubar>
+
+  <script type="application/javascript"><![CDATA[
+    function ok(condition, message) {
+      window.opener.wrappedJSObject.SimpleTest.ok(condition, message);
+    }
+
+    function onTestsFinished() {
+      window.close();
+      window.opener.wrappedJSObject.SimpleTest.finish();
+    }
+
+    var fooCallCount = 0;
+    function foo() {
+      fooCallCount++;
+      let instruction = document.createProcessingInstruction("xml-stylesheet", 'href="chrome://foo.css" type="text/css"');
+      document.insertBefore(instruction, document.documentElement);
+      if (fooCallCount == 2) {
+        ok(true, "If we got here we didn't crash, excellent.");
+        onTestsFinished();
+      }
+    }
+
+    function onLoad() {
+      foo();
+      setTimeout(function() foo(), 0);
+    }
+  ]]></script>
+</window>

new file mode 100644
--- /dev/null
+++ b/widget/tests/test_bug586713.xul
@@ -0,0 +1,34 @@
+<?xml version="1.0"?>
+<?xml-stylesheet href="chrome://global/skin" type="text/css"?>
+<?xml-stylesheet href="chrome://mochikit/content/tests/SimpleTest/test.css"
+                 type="text/css"?>
+<window title="Native menu system tests"
+  xmlns:html="http://www.w3.org/1999/xhtml"
+  xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+
+  <title>Native menu system tests</title>
+  <script type="application/javascript" 
+          src="chrome://mochikit/content/MochiKit/packed.js"></script>
+  <script type="application/javascript"
+          src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js" />
+
+<body  xmlns="http://www.w3.org/1999/xhtml">
+<p id="display"></p>
+<div id="content" style="display: none">
+  
+</div>
+<pre id="test">
+</pre>
+</body>
+
+<script class="testbody" type="application/javascript">
+<![CDATA[
+
+SimpleTest.waitForExplicitFinish();
+window.open("bug586713_window.xul", "bug586713_window", 
+            "chrome,width=600,height=600");
+
+]]>
+</script>
+
+</window>