I think you’re right and that I’ve horribly misunderstood how this data is collected and used. According to their yearly report, mozilla’s advertising revenue is explicitly not drawn from user data and is only related to tiles and default search engine sponsorships. The fact that they are not selling this information is heartening and it inspires confidence that they have not flipped on the ad money spigot.
But we’re there any better platforms that people were using? The problem was that all the alternatives were doing next tot nothing for countering disinformation. Twitter was the best of a bad situation.