Before the recent API purge, you could access public data from sites like Reddit and Twitter pretty easily too. I mean it's still easy now, just not free. The same thing used to be true for Facebook, but their API purge was several years ago and their data model made less data straightforwardly public.
Personally I'd rather have my public posts be straightforwardly public than the illusion of privacy provided by sites like Facebook. Maybe a lot of people can get away with treating messages to a private Facebook group as private a lot of the time, but it's simply a wrong mental model that will lead to wrong decisions. A message can either be private or be broadcast to an open-ended set of people - not both.
Firefox died long ago.
It was an engine fight, and Mozilla decided not to participate.