Puoi fare cosi ( non testato con FF )

codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>
<head>
<title>Untitled</title>
<style type="text/css">
<!--
#object1 {position:absolute; visibility:show;top:0px; z-index:999;
          height:200px;width:200px;background-color:#ffffcc;border:1px solid blue}
-->
</style>

<script language=javaScript>

var movingMenuWidth = 0;
var menuNameColor   = "";
function setVariables(){
 if (navigator.appName == "Netscape") {
  v=".top=";dS="document.";sD="";y="window.pageYOffset"
 } else {
  v=".pixelTop=";dS="";sD=".style";y="document.body.scrollTop"
 } //  if (navigator.appName == "Netscape")
} // function setVariables()

function checkLocation(){
 object="object1";yy=eval(y);eval(dS+object+sD+v+yy);setTimeout("checkLocation()",10)
} // function checkLocation()

function menuHideShow(td, object1) {
 if (object1.style.left == movingMenuWidth+"px") {
  object1.style.left = 0;
	menuNameColor      = td.style.color;
	td.style.color     = 'yellow';
 } else {
  object1.style.left = movingMenuWidth;
	td.style.color     = menuNameColor;
 } //  if (object1.style.left == movingMenuWidth+"px")
} // function menuHideShow(object1)

</script>

</head>
<body>
<div id="object1" style="">
pippo
</div>












































































<script language="JavaScript" type="text/javascript">
<!--
movingMenuWidth = document.getElementById('object1').offsetWidth  * -1;
setVariables();checkLocation();
//-->
</script>

</body>
</html>