//alert(navigator.userAgent);
if(navigator.appVersion.indexOf("Mac") != -1)
{
    if(navigator.userAgent.indexOf("Safari") != -1)
    {
        document.write("<link href=\"_css/SiteStyles_mac_safari.css\" rel=\"stylesheet\" type=\"text/css\"></link>");
    }
   else if(navigator.userAgent.indexOf("Firefox") != -1)
    {
        document.write("<link href=\"_css/SiteStyles_mac_firefox.css\" rel=\"stylesheet\" type=\"text/css\"></link>");
    }
}