Same problem here, began immediately after booting and updating to 150. Other websites running normally. Cleared history and cache, currently in troubleshooting mode, but no Facebook. Just a blank page.

Thank you both and reporting, we are tracking the issue here: https://github.com/webcompat/web-bugs/issues/217280

Hack that worked for me:

Open about:config, search for security.tls.version.max and change it from 4 to 3.

Just tried that and yes it does solve my problem. No idea why though.

Because something sitting between the browser and Facebook's delivery edge doesn't like the connection using the most modern protocols — while using a fallback one connects correctly. (Flipping this pref basically disables some necessary prerequisites right away for the HTTP/3 to even happen.)

Is it possible that you use some antivirus or security software, like Bitdefender?

I do indeed use Bitdefender, but that doesn't explain why Facebook always worked well until that time in the afternoon when Firefox updated to 150 and why it continued to work with other browsers with no problem. But the small change suggested above did solve the problem, so it must be a change in Firefox that caused the problem.

Hi all, this issue should be resolved with the next Firefox update. Meanwhile, disabling BitDefender or turning off its traffic filtering features may help.

For reference, see bug 2034178 (particularly, this comment). Long story short, an implementation of a new HTTP/3 feature was introduced in v150, which BitDefender wasn't ready for. As a result, BitDefender's traffic filtering corrupts server responses that use this feature (which is the case with Facebook).

I'm sorry, but I really don't see turning off my virus protection as a safe way to solve this problem. The suggestion by dbert721 above has solved the issue for the moment.