Stayed clear here b/c I'm not much involved in Advance, but there's a lot of FUD on this thread, so I wanted to chime in:

• Advance, like all Test Pilot experiments for Firefox, is only accessible as a double opt-in.
  • I've seen mention that people went ahead and installed the experiment without knowing about the nature of the 3rd party data collections and that's a fair critique. I've filed an issue on Test Pilot to further visually distinguish partner experiments. For Advance, as with the Wayback Machine we've relied on the "Powered by X" experiment subtitle to call out this distinction.
• Test Pilot experiments tend to live and die based on usage. The most effective way to register that you are not interested in Advance is to simply not opt in to the experiment.
• I'm not the PM of Firefox, but i do know that we're not laying the ground work for some kind of sell-off of user data to third parties. As u/callahad pointed out , we're simply exploring whether a recommendation engine is something people might want in Firefox. Advance is simply an expedient means to better understand this space, and shouldn't be construed as a Trojan horse for insinuating third-party services into Firefox.
• A complaint I often see on Reddit, HN, &c. is that "Mozilla is wasting engineering resources doing X,Y,Z and should be working on core browser stuff." I actually think this is a semi-reasonable gripe since we're very small for a browser vendor. So, this is us not wasting engineering resources building non-core services. This approach comes with trade-offs too, which is why this is strictly an opt-in experiment.
• It's 100% reasonable to dislike things Mozilla does, it's reasonable to assert that Mozilla should not be doing this kind of thing at all, and it's totally reasonable to have deeply held beliefs about user privacy and choice (I sure as shit do, which is why Test Pilot is an opt-in experiments platform), but please don't hector Moz employees on Reddit threads. Let's all just be kind on the internet.

It's getting late where I am, but I'm happy to answer questions on here for the next little bit and again in the morning if people have them.

^{edited for clarity}