Hehe, did you just use the sample javascript code mozilla giving you?
(not saying you're taking false credit or anything, but it looks exactly the same)

<script language=javascript><!--
function addEngine(name,ext,cat)
{
if((typeof window.sidebar=="object")&&(typeof window.sidebar.addSearchEngine=="function"))
{
window.sidebar.addSearchEngine("http://www.stevengibbons.com/tfl/"+name+".src","http://www.stevengibbons.com/tfl/"+name+"."+ext,name,cat);}
else
{
errorMsg(name,ext,cat);}
}
//-->

</script>