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.

I'd imagine that's the reason it's not enabled by default, they're not finished fully implementing it in Firefox yet.

Probably because they don't leverage cosmetic filtering yet: https://docs.rs/adblock/latest/adblock/struct.Engine.html#me...