* "Clear the Cache": Tools > Options > Advanced > Network > Offline Storage (Cache): "Clear Now" * "Remove the Cookies" from sites that cause problems: Tools > Options > Privacy > Cookies: "Show Cookies" ---- Start Firefox in [[Safe Mode]] to check if one of the add-ons is causing the problem (switch to the DEFAULT theme: Tools > Add-ons > Themes). * Don't make any changes on the Safe mode start window. See: * [[Troubleshooting extensions and themes]] ---- Another possible cause is security software (firewall) that blocks or restricts Firefox without informing you about that, possibly after detecting changes (update) to the Firefox program. Remove all rules for Firefox from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process. See: * [[Server not found]] * [[Firewalls]]