Check the connection settings. *Tools > Options > Advanced > Network : Connection > Settings *https://support.mozilla.org/kb/Options+window+-+Advanced+panel If you do not need to use a proxy to connect to internet then try to select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly. See "Firefox connection settings": *https://support.mozilla.org/kb/Firefox+cannot+load+websites+but+other+programs+can You can check for problems with preferences.<br /> Rename or delete the prefs.js file and possible numbered prefs-##.js files and a possible user.js file to reset all prefs to the default value. *http://kb.mozillazine.org/Preferences_not_saved *http://kb.mozillazine.org/Resetting_preferences