document.write('<link rel="stylesheet" type="text/css" href="'); 
var agt = navigator.userAgent.toLowerCase(); 

// Check for FireFox
if (agt.indexOf('gecko') != -1)
{
    document.write('firefox.css'); 
}
// Check for Chrome
else if (agt.indexOf('chrome') != -1)
{
    document.write('firefox.css'); 
}
// Check for IE
else if (agt.indexOf('msie') != -1)
{
    document.write('main.css');
}
// Default to IE (sorry Opera...)
else
{
    document.write('main.css'); 
}
document.write('" >');