diff -r 000000000000 -r 6474c204b198 js/src/tests/ecma_3/Array/regress-390598.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/tests/ecma_3/Array/regress-390598.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,40 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+
+//-----------------------------------------------------------------------------
+var BUGNUMBER = 390598;
+var summary = 'Override inherited length of Array-like object';
+var actual = '';
+var expect = '';
+
+
+//-----------------------------------------------------------------------------
+test();
+//-----------------------------------------------------------------------------
+
+function test()
+{
+  enterFunc ('test');
+  printBugNumber(BUGNUMBER);
+  printStatus (summary);
+ 
+
+  function F() {} 
+  F.prototype = []; 
+
+  // override inherited length from the prototype.
+  expect = 10;
+  var x = new F(); 
+
+  print('x = new F(); x instanceof Array: ' + (x instanceof Array));
+
+  x.length = expect;
+  actual = x.length;
+
+  reportCompare(expect, actual, summary);
+
+  exitFunc ('test');
+}