Firefox freezes, whenever I open a youtube video. The search on youtube still works fine. Youtube still works in Edge. Once it freezes, I can't kill the process (I tried Task manager, Process Explorer, Process Hacker, command prompt) and thus I can't restart Firefox. I can't delete the parent.lock file in my profiles folder, until I reboot. If I don't delete that file after a reboot, I still can't start firefox. I have tried to start in safe mode, which didn't help and I have reinstalled the newest version of Firefox, which didn't help either. I have deleted my cache and history multiple times throughout trying to fix this.

I was watching one youtube video, and then switched to another and then the problem started, so the first occurence seems random to me.