Layer script not working in Firefox

[ericaalicen]

I'm not very javascript savvy, but it seems to me that firefox should work like ns6 from other postings I've looked at. Any ideas how to make this work in Firefox?

<SCRIPT LANGUAGE="JavaScript">

<!-- Begin
var ie4 = (document.all) ? true : false;
var ns4 = (document.layers) ? true : false;
var ns6 = (document.getElementById && !document.all) ? true : false;
function hidelayer(lay) {
if (ie4) {document.all[lay].style.visibility = "hidden";}
if (ns4) {document.layers[lay].visibility = "hide";}
if (ns6) {document.getElementById([lay]).style.display = "none";}
}
function showlayer(lay) {
if (ie4) {document.all[lay].style.visibility = "visible";}
if (ns4) {document.layers[lay].visibility = "show";}
if (ns6) {document.getElementById([lay]).style.display = "block";}
}
function writetolayer(lay,txt) {
if (ie4) {
document.all[lay].innerHTML = txt;
}
if (ns4) {
document[lay].document.write(txt);
document[lay].document.close();
}
if (ns6) {
over = document.getElementById([lay]);
range = document.createRange();
range.setStartBefore(over);
domfrag = range.createContextualFragment(txt);
while (over.hasChildNodes()) {
over.removeChild(over.lastChild);
}
over.appendChild(domfrag);
}
}
// End -->
</script>


<SPAN ID="a" style="position:absolute;visibility:hidden;"><img src="images/aboutusfrt.jpg" width="222" height="287" alt="" border="0"></SPAN>


<a href="about.htm" onmouseover="document.about.src='images/nav2_about_on.gif';showlayer('a');" onmouseout="document.about.src='images/nav2_about_off.gif';hidelayer('a');"><img src="images/nav2_about_off.gif" width="152" height="24" alt="" border="0" name="about"></a>