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It is possible that your security software (firewall, anti-virus) 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 install 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 *https://support.mozilla.org/kb/fix-problems-connecting-websites-after-updating ---- You can check if you can start Firefox in <u>[[Safe Mode|Safe Mode]]</u> by holding down the Shift/Options key. *https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration *https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes