If you don't think that's about advertising, then I guess they've managed to sneak "Firefox Suggest" in there without you noticing that its main purpose is to show you ads unless you take the time to find out how to opt out.
"Firefox Suggest results may also include contextual suggestions from the Web and occasional sponsored suggestions from Mozilla's partners, which are also on by default."
They extract sensitive data from the users, but simply promise not to keep it except in anonymized aggregate form. They talk about and acquire a venture that specializes in collecting such data for advertisers but promises to keep to it only in a super-secret encrypted computing enclave. It's the sort of thing Mitchell Baker often talked about wanting to do, in various interviews. They are aiming to turn Firefox into an ad platform.
I imagine they'll probably fail and give up eventually, but who knows how much more damage will have been done by then.