diff --git a/js/tests/e4x/Regress/regress-407323.js b/js/tests/e4x/Regress/regress-407323.js
new file mode 100755
index 00000000000..6ff6c353c13
--- /dev/null
+++ b/js/tests/e4x/Regress/regress-407323.js
@@ -0,0 +1,67 @@
+/* -*- Mode: java; tab-width:8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+
+/* ***** 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 JavaScript Engine testing utilities.
+ *
+ * The Initial Developer of the Original Code is
+ * Mozilla Foundation.
+ * Portions created by the Initial Developer are Copyright (C) 2007
+ * 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 ***** */
+
+gTestfile = 'regress-407323.js';
+
+var summary = 'XML, XMLList, QName are mutable, Namespace is not.';
+var BUGNUMBER = 407323;
+var actual = '';
+var expect = '';
+
+printBugNumber(BUGNUMBER);
+START(summary);
+
+var obj           = {};
+var saveQName     = QName;
+var saveXML       = XML;
+var saveXMLList   = XMLList;
+var saveNamespace = Namespace;
+
+QName = obj;
+TEST(1, obj, QName);
+
+XML = obj;
+TEST(2, obj, XML);
+
+XMLList = obj;
+TEST(3, obj, XMLList);
+
+Namespace = {};
+TEST(4, saveNamespace, Namespace);
+
+END();
diff --git a/js/tests/js1_5/Regress/regress-407323.js b/js/tests/js1_5/Regress/regress-407323.js
new file mode 100755
index 00000000000..d07f9966179
--- /dev/null
+++ b/js/tests/js1_5/Regress/regress-407323.js
@@ -0,0 +1,75 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* ***** 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 JavaScript Engine testing utilities.
+ *
+ * The Initial Developer of the Original Code is
+ * Mozilla Foundation.
+ * Portions created by the Initial Developer are Copyright (C) 2007
+ * 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 ***** */
+
+var gTestfile = 'regress-407323.js';
+//-----------------------------------------------------------------------------
+var BUGNUMBER = 407323;
+var summary = 'XML, XMLList, QName are mutable, Namespace is not.';
+var actual = '';
+var expect = '';
+
+
+//-----------------------------------------------------------------------------
+test();
+//-----------------------------------------------------------------------------
+
+function test()
+{
+  enterFunc ('test');
+  printBugNumber(BUGNUMBER);
+  printStatus (summary);
+ 
+  var obj           = {};
+  var saveQName     = QName;
+  var saveXML       = XML;
+  var saveXMLList   = XMLList;
+  var saveNamespace = Namespace;
+
+  QName = obj;
+  reportCompare(obj, QName, summary + ': QName');
+
+  XML = obj;
+  reportCompare(obj, XML, summary + ': XML');
+
+  XMLList = obj;
+  reportCompare(obj, XMLList, summary + ': XMLList');
+
+  Namespace = {};
+  reportCompare(saveNamespace, Namespace, summary);
+
+  exitFunc ('test');
+}