There's a popup that YouTube has started showing these days that tells you "AdBlockers are illegal. Stop using them" or something to that effect. This blocks that popup from appearing.
Somehow I still haven't seen that message despite also using uBlock and Firefox. Perhaps I'm just further down the line and Google will eventually come for me too, but I wonder if my DuckDuckGo and Privacy Badger extensions may also have something to do with it.
I keep getting that pop-up, I have had ublock installed for years. I haven't done anything special to unlock and just refresh the page and it goes away.