Ciao,

navigator.userAgent

ES:

codice:
<script type="text/javascript">
browsername=navigator.userAgent;
if (browsername.indexOf("Firefox")!=-1) {
document.write("USI FIREFOX")
}
if (browsername.indexOf("MSIE")!=-1) {
document.write("USI MSIE")
}
</script>
Massimo.