Cross-posting my comment from the post you cross-posted (and possibly created your account just to post?)
After reading about the actual feature (more), this seems like an absolutely gigantic non-issue. Like most anti-Mozilla stories end up being.
The whole thing is an experimental feature intended to replace the current privacy nightmare that is cross-site tracking cookies. As-implemented it's a way for advertisers to figure out things like "How many people who went to our site and purchased this product saw this ad we placed on another site?", but done in such a way that neither the website with the ad, nor the website with the product, nor Mozilla itself knows what any one specific user was doing.
The only thing I looked for but could not find an answer on one way or the other is if Mozilla is making any sort of profit from this system. I would guess no but actually have no idea.
There are definitely things that can be said about this feature, like that users with pre-existing installs should have been asked to have it turned on (for optics alone, apparently), or that its mission of replacing tracking cookies is unlikely to succeed. But the feature itself has virtually no privacy consequences whatsoever for anybody.
I'm absolutely convinced there's a coordinated anti-Firefox astroturfing campaign going on lately.