> There was a time when users of Facebook and users of Google Talk were able to chat with each other and with people from self-hosted XMPP servers This is fals

> There was a time when users of Facebook and users of Google Talk were able to chat with each other and with people from self-hosted XMPP servers This is false. While it's true that Google Talk did adopt XMPP for a time, Facebook never did. They ran a little client bridge so that people could sort-of use third-party clients, but you could never communicate between Google Talk and Facebook users over XMPP.