You may need to reinstall the latest Firefox version to recover from a system restore. Using "System Restore" can cause your Firefox installation to get corrupted because not all files are restored (only files in a white-list), so be cautious with using System Restore.<br /> You need to (re)install software that was affected.<br /> Remove the Firefox program folder (C:\Program Files\Mozilla Firefox\) before reinstalling a freshly downloaded Firefox copy to do a clean install. ----- A possible cause is security software (firewall) that blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program. Remove all rules for Firefox and the plugin-container 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 and the updater process. See: *https://support.mozilla.org/kb/Server+not+found *https://support.mozilla.org/kb/Firewalls