Privacy: We've heard of it.

I am a big fan of irony. I find it delicious that Firefox recommends that the way to 'protect your privacy' is to 'Join Firefox', thereby immediately sharing your email address to the world, and agree to a 'privacy policy' which promises to essentially collect every bit of information it possibly can and share it essentially to every corner of the Internet. Step one? Immediately pass your email address on to a 'partner' that will share it with anyone they wish.
By default, Firefox collects and shares any and all data available from anywhere it can, including "data that identifies you or is otherwise sensitive to you" from an unlimited number of third and fourth parties.
Data is sent to third parties, each of which has its own privacy policy. Each in turn confesses to acquiring anything they can, storing it, and further sharing it on to fourth parties. Third parties are not limited to, but explicitly include:
Pocket Recommendations, Adzerk, Google, Adjust, Leanplum, 'search partners', your search provider, SalesForce, Firefox connected services (Lockwise, Monitor, Notes Send, Firefox Screenshots and Sync), and Mozilla.