If Firefox baked in ad blocking, they would have to then deal with the financial incentive to make it worse. Sponsored ads, 'good' ads, government announcements, election propaganda... there is a slippery slope they are better off not getting on. A trusted 3rd party from the wider community seems a better option in many ways. The alternative is starting a web browser with a manifesto welded on that essentially states 'death to all advertising', and until that can be crowd funded I can't see that happening in today's world.

What I am surprised about is that none of the browsers or forks have created a specialist plugin API for adblocking and maybe other filtering. Provide what is needed and only that (keeping the surface tiny), and then evolve the general purpose API in the way they need. I don't think we need V2 of the API any more, except for keeping this one absolutely critical plugin working, do we?