@Schouten_B I do not agree that this system is "completely different" from Google's. It is hard to tell because Firefox has disclosed less information than Google has (perhaps there is another document with technical details somewhere else) but my initial read of the information I have is that Google's "Ad Lab"/"Ad Privacy" comprises three reporting features and Firefox has implemented a specific one of them wholesale, apparently (per their statement) with an eye to formalizing it as a standard.
@mcc I believe that is because the list of sites enrolled is not set, but any site can request a token to participate. I.e. it is open, but with some additional safeguards.
I believe the currently enrolled sites are available publicly, but I'd need to check.