> Everything can be disabled.

If it is enabled by default, then they are doing it wrong.

That's just your opinion. I do not mind sharing data with them by default because I know the data helps their long-term survival. Especially because I know I'm lazy (like most people are) so if it's opt-in I wouldn't bother turning things on.

> I do not mind sharing data

That's just your opinion. Mozilla should be very clear, up front, about what data they collect by default[1], so that users can make educated decisions about whether to allow it. This whole "we promise to protect everything (lol) we collect about you" PR stunt obscures the fact that they are collecting data from users by default.

1. They 'detail' it in the privacy policy, but 1) almost all end users will not see a link to it and 2) almost all end users will not consider that Mozilla is collecting data from them by default.

It should be noted that, though you personally may be consistent about this, most people would consider identical opt-in data sharing on the part of eg Chrome to be evidence of Google's dastardliness. I don't think it's unreasonable to expect Mozilla not to take user data by default if they're positioning themselves as privacy-oriented.