"Must visit from" javascript wont work in IE...

I have obtained the following script which only lets a page load if the visitor has been to the previous page, if they haven’t it sends the visitor to the appropriate page. However, it only works in Mozilla. Can anyone help me adapt this script to work in Internet Explorer?

<SCRIPT LANGUAGE="JavaScript" > 
<!-- Begin
var requiredfrom = "http://domain.com/somepage.htm"; //  required prev. page
if (document.referrer.indexOf(requiredfrom) == -1) {
alert("You must logon first...");
window.location=requiredfrom;
}
//  End --> 
</script>

Cheers,
NuGG