sounds like it just uses ublocks lists.
though it doesn’t seem to work as well as ublock, the ad slots are still there with just the ad missing so there’s a giant ugly blank spot.
Probably because they don't leverage cosmetic filtering yet: https://docs.rs/adblock/latest/adblock/struct.Engine.html#me...
I'd imagine that's the reason it's not enabled by default, they're not finished fully implementing it in Firefox yet.