Could you try Firefox's Safe Mode? That's a standard diagnostic tool to bypass interference by extensions (and some custom settings). More info: Diagnose Firefox issues using Troubleshoot Mode.

If Firefox is running, you can restart Firefox in Safe Mode using

Help > Restart with Add-ons Disabled

(If Firefox is not running, you can start Firefox in Safe Mode by holding down the Shift key when double-clicking the Firefox icon.)

In the small dialog that should appear, click "Start in Safe Mode" (not Reset)

Any difference?

Also, do bookmarks work? And/or does the search bar (the one to the right of the address bar) work?

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