I'm on a Mac using Mac OS Big Sur, 11.7.10. Videos will not play on Firefox, whether on Youtube, in social media, on websites, or whatever. Sometimes the video will play with no audio, sometimes I just getting a rolling wheel. I have other functionality issues that may be related. I don't want to close and restart all the time. I am considering changing to a new default browser over the issue. If I switch to Chrome or Safari, the videos play fine. Which seems like my answer.