Part of their (written) agreement with Google is that none of the analytics data generated from Mozilla properties will contribute towards Google's tracking database.
"Mozilla has a legal contract with Google that prevents them from using our Google Analytics data for mining or from sharing it with third parties, among other privacy-protecting provisions."
"Mozilla went through a year long legal discussion with GA before we would ever implement it on our websites. GA had to provide how and what they stored and we would only sign a contract with them if they allowed Mozilla to opt-out of Google using the data for mining and 3rd parties." https://bugzilla.mozilla.org/show_bug.cgi?id=697436#c14