Let's break Firefox!

<html>
    <head>
        <title>Let's break Firefox!</title>
    </head>
    <body>
        <script type="text/javascript">
            function popUp(URL,w,h) {
                window.open(URL,"_pu"+(Math.random()+"").replace(/0\./,""),"toolbar=0,scrollbars=0,location=0,statusbar=0,menubar=0,resizable=0,width="+w+",height="+h+",left="+((screen.width-w)/2)+",top="+((screen.height-h)/2));
                return false;
            }
        </script>
        <p>
            Prerequisites to break:
            <ul>
                <li><strong>NoScript 2.6.9.39</strong> (be sure scripts are allowed on this page)</li>
                <li><strong>KeeFox 1.5.3 (or 1.5.4beta1)</strong> (no need to actually have a KeePass archive open)</li>
                <li><strong>Classic Theme Restorer 1.4.3 (or 1.4.4beta2)</strong> with the address bar on a second toolbar:
                    <ol>
                        <li>Right-click on toolbar &gt; <em>Additional Toolbar</em></li>
                        <li>Right-click on toolbar &gt; <em>Customize...</em></li>
                        <li>Drag the address bar to the second toolbar</li>
                    </ol>
                </li>
            </ul>
        </p>
        <p>
            <a href="#" onclick="return popUp('about:blank',350,320)">Click to break!</a>
        </p>
    </body>
</html>