http://javascript.about.com/library/blbrsdet.htm

codice:
function whichBrs() {
var agt=navigator.userAgent.toLowerCase();
if (agt.indexOf("opera") != -1) return 'Opera';
if (agt.indexOf("phoenix") != -1) return 'Phoenix';
if (agt.indexOf("firefox") != -1) return 'Firefox';
if (agt.indexOf("safari") != -1) return 'Safari';
if (agt.indexOf("msie") != -1) return 'Internet Explorer';
if (agt.indexOf("netscape") != -1) return 'Netscape';
if (agt.indexOf("mozilla/5.0") != -1) return 'Mozilla';
}