Microsoft decided to turn on DNT by default in Windows 8 / MSIE 10, which led to a violation of the DNT standard and a complicated debacle which rendered the whole thing pointless. It was a silly idea and an even sillier outcome, but that does not make the ideal itself silly.

> They won't stop

Then we can rip this out later, or submit a patch to opt everyone out. I trust Mozilla to accept such a patch much more than I do Google. It's not irreversible, it's an ongoing negotiation.

> Thought experiment:

Your thought experiment ignores the rationale Mozilla provided. I think ideally we would be notified on first upgrade / out of box that we are opted in to sharing our preferences with advertisers in a limited way, with a nice obvious "Opt out" button in that notification. That way, legitimate advertisers get the limited conversion rate information they desperately want from enough people who aren't interested one way or the other, and those who are diametrically opposed to the entire concept are perfectly able to turn it off before their first browsing action.

But I also don't think they'd build an interface this extensive for what they describe as a limited test run against a handful of allow-listed sites for exploratory and standards-determining reasons. I would have liked to at least see a heads-up upon the activation of this system in those cases, since that seems easy enough to build for a test run.