css script doesn't work in FF

[darkdusky]

Hi I am using the following snippet in my website to have tabs along the top. The tabs change colour if the user is on a particular page. This works in IE, Chrome and Safari, but not FireFox.
Here is the relevant code:

<script type="text/javascript">

        function setActiveMenu() {
            var control = document.getElementById('tabid');
            var menuid = control.innerText;
            var menu = document.getElementById(menuid);
            menu.className = 'current';
        }

        window.onload = setActiveMenu;  
    
    
    </script>

This is the webpage where I got the sample:
http://www.dynamicdrive.com/style/cs...dd-color-tabs/