What is less clear is: to what extent is Facebook the press? The press, in 1789, could not send you push notifications. It was not gamified with the intent of increasing user engagement. It was not interwoven with a person's private communications with their friends. It did not encourage users to build "profile pages" on which they hang their reputations and opinions. Someone might have seen you reading The Federalist Papers, but everything else was up to you.
Any of these provides a legal avenue to regulate Facebook without cheapening the broad freedoms prescribed to actual publishers. James Madison never dreamed that a Senator would send messages to his constituents that make their phones buzz when they aren't being looked at. In my unvarnished opinion, that's not freedom of the press, it's something else.