There is a ability, iirc for extensions to use your Mozilla Sync account for storing settings. However it´s up to each extension developr to include this.

how are you watching YouTube without ads?

My controversial way (probably will be downvoted) is with Premium to support content creators i enjoy.

But to answer your question; My understanding is Brave Browser (despite WebKit) and AdGuard with Safari also removes ads.

Thanks for keeping the community updated and for all the work you put into maintaining it!