Are there any changes made to network.http prefs?

• Open the about:config page via the location bar and do a search for network.http via the Search bar at the top of the about:config page.
  
• Reset all network.http related prefs that appear bold (user set) via the right-click context menu to their default values.

• http://kb.mozillazine.org/about:config

See also http://kb.mozillazine.org/Resetting_preferences

I did not reset becuase few minutes later after your reply, google started working well, but since yesterday the problem has returned. I do not know if I have to wait again or what? It has never happened when I had lower version of Mozilla Firefox.

please reset the preferences, cor-el has described - in particular network.http.keep-alive should be set to true!