A possible cause is security software (firewall,anti-virus) 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 *http://kb.mozillazine.org/Browser_will_not_start_up ---- If you can't uninstall Firefox then you can delete the Firefox program folder manually from your hard drive. *C:\Program Files\Mozilla Firefox\ *C:\Program Files (x86)\Mozilla Firefox\ *http://kb.mozillazine.org/Installation_directory *http://kb.mozillazine.org/Uninstalling_Firefox Download a fresh Firefox copy and save the file to the desktop. *Firefox 16.0.x: http://www.mozilla.org/en-US/firefox/all.html Do NOT remove personal data when you uninstall your current Firefox version, because all profile folders will be removed and you will also lose your personal data like bookmarks and passwords from profiles of other Firefox versions. ---- *http://kb.mozillazine.org/Profile_folder_-_Firefox *http://kb.mozillazine.org/Profile_backup *http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall