Check if your firewall cause this : [https://support.mozilla.org/en-US/kb/configure-firewalls-so-firefox-can-access-internet?redirectlocale=en-US&redirectslug=Firewalls Configure firewalls so that Firefox can access the Internet] see also: [https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can Firefox can't load websites but other browsers can] thank you Please mark "Solved" the answer that really solve the problem, to help others with a similar problem.

try to uninstall avg (& include the "remove all user settings" option) & install it again afterwards if you suspect something has gone wrong with the configuration... or you could try a different antivirus program - [http://windows.microsoft.com/mse ms security essential]s is quite reliable and lightweight for example...