Firefox

Opt-in is only meaningful if users can make an informed decision. I think explaining a system like PPA would be a difficult task. And most users complain a lot about these types of interruption.

In my opinion an easily discoverable opt-out option + blog posts and such were the right decision.

So you see, because the users can't meaningfully give informed consent, their consent is therefore uh... [checks notes] not necessary.

Bullshit. Everyone knows that it's because if you actually ask someone "do you want to be creepy tracked, less-creepy tracked, or not tracked?" they'll pick "not" every time.