If it doesnt start you can try to reinstall, but when you are DO NOT check to delete personal info.

If a reinstall doesn't work, try to create a new profile using the profile manager.

• Profile Manager - Create, remove or switch Firefox profiles
• Recovering important data from an old profile

Also make sure your firewall/AV is not blocking Firefox.

• Firefox won't start - find solutions

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 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

• https://support.mozilla.org/kb/fix-problems-connecting-websites-after-updating