I have ad blockers and anti-tracking extensions, but they don’t do anything against this new feature because it’s the browser itself doing it.
I don’t think that’s the case. If you have e.g. uBlock, the API for this new feature won’t be called, even if enabled, according to Colin (developer for Multi-Account Containers) in the Mozilla General matrix chat. I’d lean towards trusting Colin over you, here.
And, please, don’t bother Colin over this. I only mention him because if I didn’t, I just know some people would downvote without even bothering to ask for a source, despite never providing any source for the opposite themselves.
I get your point, and your frustration, but please don’t talk so confidently about things you aren’t actually certain of.