var ua = navigator.userAgent.toLowerCase(); 
//alert(ua);
/*If mac safari*/if (ua.indexOf('safari/') != -1 ){document.write('<link href="/css/macstyle.css" rel="stylesheet" type="text/css" media="screen" />');}
/*If mac firefox3*/if((ua.indexOf('firefox/') != -1) && ua.indexOf('macintosh') != -1 ){document.write('<link href="/css/macstyle.css" rel="stylesheet" type="text/css" media="screen" />');}