This can not realistically end up as a addon and also will not gain any traction as opt-in option, it needs to be opt-out. So it's either going to be abandoned or end up baked in.

So, unless a considerable part of the userbase is "throwing a tantrum", this will be yet another thing I have to remember to turn off on fresh installs.

Not fighting this kind of erosion tooth and nail at every step endangers the only viable, fully featured, alternative to the Googles browser. Yes, Mozilla needs to be held to a higher standard, the alternative is the inversion of what it stands for.

I have honestly no idea how one can look at this and go yeah, that seems like its in tune with our values.

The next question that follows is "who at Mozilla instigated this and why?". The mindset at Mozilla seems to have changed somewhat.

It might be opt-out, but it needn't necessarily send your data to a third party or even Mozilla if it ever does get baked in. They're also experimenting with finding ways to do machine learning client-side.