Mozilla's funding comes almost exclusively from Google.
Many plugins have been written to protect Firefox users from having their personal info being collected by Google. If Mozilla put the users' interests first, it would include some of these plugins in their official version of Firefox. But they don't. Their top priority is getting funding from Google.
Further, they use their trademark policy to make it problematic for redistributors to add privacy features.
Users should choose the version of Firefox that serves their needs. Mozilla's official version is the weakest in terms of privacy protection, so users should avoid it.