It's more that a lot of people really don't care one way or another, and will neither go out of their way to opt-in or opt-out.
Additionally, it's not that Mozilla just disregards user privacy here: differential privacy being used would mean that no user has to reveal their private information, but looking at all the data in aggregate would still allow Mozilla to gain useful information on how to make Firefox better.
Additionally, it's not that Mozilla just disregards user privacy here: differential privacy being used would mean that no user has to reveal their private information, but looking at all the data in aggregate would still allow Mozilla to gain useful information on how to make Firefox better.