I made this project for a hackathon with two of my buddies in 2016, taking 2nd out of 98 teams.
Back when I begrudgingly used facebook to chat to some friends, I came up with the idea of end to end encrypting facebook messages to those friends.
We wrote a basically transparent browser extension that let you encrypt facebook messages with RSA.
Facebook made it clear they didn't like what we were doing, and in the week after we won (and got a little news attention), started changing their html to make our kind of extension a lot harder.
Our extension worked great, but none of us used facebook enough to make it worth maintaining, and now you allegedly have facebook chats "end to end" encrypted by facebook itself.
There's surely no way that facebook could circumvent their own safeguards, right?