var userAgent = navigator.userAgent.toLowerCase();
var is_op = (userAgent.indexOf('opera') != -1); //is opera
var is_saf = (userAgent.indexOf('safari') != -1); //is safari
var is_ie = (userAgent.indexOf('msie') != -1 && (!is_op) && (!is_saf)); //is internet explorer
var is_nn = (userAgent.indexOf('netscape') != -1); //is netscape
var is_moz = ((navigator.product == 'Gecko') && (!is_saf)); //is mozilla