From the ‘Opt-in by Default’ files:
Firefox 21 is now in Beta and it introduces a number of new features that will become generally available inside of the next 6 weeks.
At the top of the list is a new Health Reporting feature that Mozilla first publicly started talking about in September of 2012.
With the Health Report – users agree to send performance data to Mozilla. In return users get detailed information about their browser performance.
Oh but wait – users don’t have to explicitly agree to opt-into the data sharing.
According to Mozilla’s own documentation Data Sharing is on by DEFAULT.
While I understand this is all about improving performance for everyone and the information isn’t necessarily user-identifiable. I personally think that it’s hypocritical that Mozilla is pushing forward on new cookie and Do Not Track privacy policies on one hand and then automatically opting users in to share information about browser performance by default.
To be fair this is still in beta and users can opt out if they so choose. As a beta, Mozilla can still adjust the default policy before this is generally available too (and I’m hoping they do).