I think it's pretty clear, the checkbox reads: "Allow websites to perform privacy-preserving ad measurement."
Nowhere does this explicitly state that Mozilla receives non-anonymous information from the user. If anything, they do their damnedest to obfuscate this fact.
But yes, I am shocked that they did not notify their users, and I am even more shocked that they use the excuse of being too confusing, especially after the collection of pop-ups I have found them display on far more trivial things in the past.
It sells browsing and search history
But only if you use the extension. Mozilla doesn't collect that data w/o the extension being installed. If I opt-in (or not opt-out) to the PPA feature, that data will not go to that subsidiary, nor will it be associated with me in any way
Mozilla FakeSpot is Mozilla. Their privacy policy specifically states that data can be transferred to their parent company, and it also states that data is sold to advertisers. On the other side, Mozilla's privacy policy says that "Firefox temporarily sends Mozilla your IP address, which we use to suggest content based on your country, state, and city. Mozilla may [read: will] share location information with our partners"...
I'm not a lawyer, so I don't even know if Mozilla considers Mozilla FakeSpot to even be a partner or just a core component of the company.
Mozilla isn't an advertiser. Google and Brave are.
Mozilla now owns a subsidiary that sells geolocation and browsing history information to advertisement companies. Mozilla now owns a subsidiary that processes advertisements. Mozilla's Firefox browser now contains a data aggregation and reporting utility that's turned on by default.
If that's not an ad company, what is? Brave is one too.