For me this is fighting over semantics. It doesn’t really matter if it’s legally piracy or not since nobody is gonna go after you for it either way. It’s about whether what you’re doing is moral or the intended way. You can use adblocker, but then you’re just freeloading. Fact of the matter is that nothing is free and everything needs compensation when at scale. You can rightfully claim that YouTube shoves too many ads and that it’s a monopoly so it abuses it’s position, but at the end of the day you’re using the service without compensating for it, so you’re stealing at least something.
The problem is that browsers aren’t profitable. Mozilla need a revenue source other than donations, and that’s why they’re trying to make another product that’ll stick. They need to make money somehow. If Google stops paying them because of the antitrust lawsuit, Mozilla will probably disappear in a few months.