They say they have to default to opt-in because otherwise users will not enable this type of data collection. That, in my opinion, should be the #1 indicator that users DO NOT want this collection happening in the first place. They default to opt-in because they know most people won't opt-out, either because they forget, aren't aware that it is happening, or various other reasons.

I'm okay with them collecting any data they want to so long as it is opt-in (because I never will). Mozilla is slowly eroding their original, core values.