The little I've read bout this says that maintaining MV2 might be something as well.
If other chromium based browsers didn't have this issue, that would be great, but likely in time Youtube won't support browsers that don't have MV3. Probably still have some time though.
The google money isn't any great gotcha. It's wrong of them to have grown to be so dependant but so what? All it means is that some day the funded development will stop, just like all the forks are already.
Let them take google money for as long as it flows. You can switch to librewolf at any time if FF itself ever actually goes bad in any critical way. But there's not a lot of reason to do so until the minute that actually happens. Go ahead and take the funded work and updates as long as it exists.
Switched to Firefox yesterday, I suggest you do the same.