<!DOCTYPE html> <html> <!-- https://bugzilla.mozilla.org/show_bug.cgi?id=1221421 --> <head> <meta charset="utf-8"> <title>Test for Bug 1221421</title> <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script> <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/> <script type="text/javascript"> var x = document.documentElement.style; x.__proto__ = [1, 2, 3]; var res = 0; for (var h = 0; h < 5000; ++h) { res += x.length; } is(res, 15000, "length getter should return array length"); </script> </head> <body> <a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1221421">Mozilla Bug 1221421</a> </body> </html>