Blinking text: JavaScript+CSS

[Koobi]

Hi guys,
This is for a colleague of mine.

I'm not too familiar with JavaScript so i thought I'd ask here.
The problem is, we are trying to make some text blink every 500ms and this is the code I use:

[code]
<script type="text/javascript"><!--
function changeColour(elementId)
{
    var interval = 500;
    var colour1 = "#00f", colour2 = "#f00";
    if(document.getElementById)
    {
        var element = document.getElementById(elementId);
        element.style.color = (element.style.color == colour1) ? colour2 : colour1;
        setTimeout("changeColour('" + elementId + "')", interval);
    }
}
//--></script>
[/code]

this doesn't seem to work on Firefox for Linux.

I was hoping you could help me out with this.

Thanks for your time.