If you don't want Firefox to pause the video when you turn off the screen, just switch to desktop mode. Also... you should use something like Newpipe instead...

Firefox on iOS is pretty lame. No ad blocker and no extensions.

Desktop mode on Android's Firefox doesn't require extension... if it's not available on I-Phone, it might be soon because I think that they are starting to allow alternate browser engines.

Sounds like a great reason to not use iOS.

Nah, Orion for iOS works great with built-in ad blocking and Firefox+Chrome extensions support, and the satellite SOS helps my family with peace of mind (I had to be helicoptered out of Nevada a few years ago). It's is way less bulky and less expensive than the inReach I used to carry.

It's funny, the videos continuing to play when the screen is off, is actually a non-feature for me most of the time because it makes using the back button to get away from a video link you clicked on impossible, you end up having to click back 2-3x and then still hit the x on the little embedded video. The music is already a separate app, they should allow you to disable the background play in the normal app and have it enabled on the music app. Which maybe they do now that I think about it, but I believe when I had checked previously it was a universal setting tied to your google account, not the apps.