I don’t know.

I use it, but when I experimented with data synchronization using Firefox Sync, it simply doesn’t work, it is so unreliable and unpredictable that you can’t bet on it. It’s a real pity, because I wanted to use it for a cool thing, synchronizing data of one website, without having my own server for that website. It failed because Firefox Sync fails.

I recommend KDE Connect, it also has this function. :)
But sometimes I use this and sometimes I use that feature.

I have it too. The image randomly freezes or the entire playback freezes.
But also regular video (not live) has problems, for example it skips forward a few seconds at random moments.
I don’t know if this is something to report on bugzilla. It’s hard to report this because I would have to constantly record my screen while watching YouTube to catch the random moment when it happens.

I have uBlock and SponsorBlock. I’m on Arch Linux.