Какая разница что открывать в Фулскрин, и чужое и своё окно откроются одинаково просто, вот так:
<html>
<head>
<title>SomeDocument</title>
<meta http-equiv="Content-Type" content="text/html; charset=windows-1251">
<script language="JavaScript">
<!--
function SomeFunction(Ie,other){
x=screen.availWidth;
y=screen.availHeight;
target = parseFloat(navigator.appVersion.substring(navigator.appVersion.indexOf('.')-1,navigator.appVersion.length));
if((navigator.appVersion.indexOf("Mac")!=-1) &&(navigator.userAgent.indexOf("MSIE")!=-1) &&(parseInt(navigator.appVersion)==4))
window.open(other,"sub",'scrollbars=yes');
if (target >= 4){
if (navigator.appName=="Netscape"){
var SomeFunction=window.open(other,"SomeFunction",'scrollbars=no','width='+x+',height='+y+',top=0,left=0');
SomeFunction.moveTo(0,0);
SomeFunction.resizeTo(x,y);}
if (navigator.appName=="Microsoft Internet Explorer")
window.open(Ie,"SomeFunction","fullscreen=yes");
}
else window.open(other,"sub",'scrollbars=yes');
}
//-->
</script>
</head>
<body bgcolor="#FFFFFF" text="#000000">
<a href="#" onClick="SomeFunction('IndexII.htm','IndexII.htm')">Go fulscreen!</a>
</body>
</html>