They are collecting "certain personally identifiable information" and moreover:
"We may employ third party companies and individuals to facilitate our Service, to provide the Service on our behalf, to perform Service-related services or to assist us in analyzing how our Service is used."
This kind of behaviour is unacceptable for any privacy conscious person. If you want to collect any user data you should make it opt-in. Most Firefox users care about their privacy - that's the prime reason they use it.