Firefox is only slow on Google. Fast on other sites

I have no specific idea what could cause this, but it might be related to Google using SPDY, so you might want to check if other SPDY enabled sites like Twitter have the same problem or if the problem stays when you disable SPDY in Firefox by opening about:config in the address bar and setting network.http.spdy.enabled to false. Testing with a new profile (by running firefox.exe -p) would also be interesting. If this does not help the problem is rather in a anti-malware product or similar, that hooks HTTP connections. A proxy also might cause problems. For more generic troubleshooting hints for Firefox see http://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems.