function BrowserInfo()
{
    var ua = navigator.userAgent.toLowerCase();
    var s;
     (s = ua.match(/msie ([\d.]+)/)) ? this.ie = s[1] :
     (s = ua.match(/firefox\/([\d.]+)/)) ? this.firefox = s[1] :
     (s = ua.match(/chrome\/([\d.]+)/)) ? this.chrome = s[1] :
     (s = ua.match(/opera.([\d.]+)/)) ? this.opera = s[1] :
     (s = ua.match(/version\/([\d.]+).*safari/)) ? this.safari = s[1] : 0;
 }
 var MyBrowser = new BrowserInfo();
 
//示例
// if (MyBrowser.firefox)
// {
//     var 版本 = MyBrowser.firefox; 
// }