On my note 4 (Android 6.0.1) i'm using firefox 143.0.3 (Build #2016117407) and youtube stopped working (wheel turns then gives an error) . First i thought it's was the adblock so i disabled but that didn't fix it. So i used a proxy that also didn't worked. Then i used another browser (chrome, opera mini) and they worked. I didn't change any settings. I installed an addon User-Agent Switcher to change firefox desktop version which also didn't worked.

Edit: Opened only HTTPS mod in the options and did a full shutdown of the phone and now it works. I think youtube or someone else changed something and only HTTPS fixed that, not tech savvy enough to find why.