Can show us what you are talking about and provide links so that we can try and replicate the issue?

Mainly my personal Google Photos page, no videos will play but will play in all other browsers. Here is a link to an Amazon product video and they won't play either.

https://www.amazon.com/Icotec-Night-Stalker-Hunting-Gear/dp/B07K8W3LMD/ref=sr_1_53?dchild=1&keywords=coyote+call&pd_rd_r=0a6c1799-3e9b-4ab8-af6c-71c6e83291c1&pd_rd_w=XIvLZ&pd_rd_wg=WY5JL&pf_rd_p=0ec05f25-9534-48fe-9c3e-40b89957230e&pf_rd_r=18BX5W6WYNTPNERZRS1J&qid=1610539850&sr=8-53

It works for me. see screenshot Did you try safe mode?

Safe Mode would be a good test.

Also, Firefox on Windows 7 uses Media Foundation, Microsoft's media components, to play H.264/MP4 video. I have a copy of the old YouTube test page. Does this show your Firefox will play H.264/MP4 videos:

https://www.jeffersonscher.com/sumo/html5-video.html

(The results we want are "supported" or "probably".)