It may also be relevant that Meta is recently upsetting people in Europe for tracking and targeting people in spite of Europe's data protection rules [1].
My guess (and this is just speculation at this point) is that Meta and Mozilla think they're being clever and getting away with some "private" ad tracking and are underestimating how much damage they're doing to Mozilla's reputation.
I doubt the Anonym tech has been built into Firefox yet, but it's clear that the corporate strategic direction is to bet on some concept of "acceptable ads" like Google did in the 90s.
[0] https://www.adexchanger.com/privacy/mozilla-acquires-anonym-...
[1] https://www.reuters.com/technology/digital-rights-activists-...