This is sort of unfortunate news to me, as I take this as a sign that they won't do adblocking by default. I think this is a mistake; users want ads to be blocked. Especially on mobile, where it's more important from a perf perspective. Brave has ads blocked, Opera has ads blocked. If Firefox wants to follow the lead and be a privacy focused company like they say, then they need to block ads.
I may be in the minority, but I've never used an ad blocker. Content makers need to make a living and cutting off their ad revenue seems sleazy. That said, they may have gone too far with tracking and other excessive bloat that I might just start using one.
As soon as I can pay for the content instead, I do it.
Ads is just another way to pay... if it's too bloated (thus too expensive) you just don't get it, or go find something less bloated (aka less expensive), that's it.