Hola
aqui te dejo un codigo
<script LANGUAGE="JavaScript">
function pantallaCompleta(pagina) {
ventanita=window.open(pagina, '', 'fullscreen=yes, scrollbars=auto');
}
window.opener = top;
</script>
</script>
<title></title>
</head>
<body onLoad="pantallaCompleta('http://masnatacion.com')">
</body>
</html>