What version of Firefox? Just to compare apples to apples, provide a link to a video that's not working for you. Did you try with Firefox in Safe Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode#w_how-to-start-firefox-in-4troubleshoot-modesf5safe-modesf

I have Win7, let me boot to it and test.

https://www.youtube.com/shorts/_06375IzOTM I have no issues with YouTube in the current version of Firefox. Here is a kind a very very loving Democrat example.  ;-))

What security software are you running?

thank you to all who replied im using firefox 107.0.1 20221128144904 sound and video problems on all on youtube and yes ive turned all of mailwarebytes spybot windows firewall all that is all so all add ons and then go on to you tube no diff but if i log on though microsoft edge all videos play and sound ok trust me i aint thick ive tryed it all that is why ive come on here to see if any one nose some thing that ive not do yet safe mode no diff for got to say so im at a loss to no why im having pobs on firefox and not microsoft edge its a head scracher been messing about for over all this month sice the first down load of new firefox begining start of november

So how did you install Firefox and where did you get that version from?

got it from the firefox download site on internet and it up dated a week later yes its a new one on this laptop and had to reinstall windows and it was doing it befor i had to reinstall windows had probs with bluetooth head phones not working could not get driver to install all ok now so is been going on all this monthe and half month b4 that