User Agent

you should think in a more specific user agent,I advice you this :
Mozilla/5.0 (Macintosh; U; Macintosh; en-US; Valve Steam GameOverlay/1383158641; ) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.166 Safari/
or 
another more general UA could be :

Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727)

Best regards.