In Firefox 3.6.4 and later the default connection settings have been changed to "Use the system proxy settings".<br /> See "Firefox connection settings" in [[Server not found]] You can find the connection settings in Tools > Options > Advanced : Network : Connection<br /> If you do not need to use a proxy to connect to internet then select No Proxy ---- A 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]]