I don't know how far we got with it, but one of the ideas was to serve a generic bundle of ads, and then select which ones to display locally, based on an entirely private, client-side analysis of the browser's history. Now, that probably shouldn't have been on the new tab page, and probably not in Firefox at all, but if ads are going to be the way we fund the Internet, then that sounded like the best possible outcome: better targeting without remote tracking. Heck, even Brave ran with the idea for a while: https://brave.com/about-ad-replacement/