I used FB Messenger over XMPP for the last handful of years before it was shut down using Pidgin and I'm pretty sure that's how it worked. You could talk to peo

I used FB Messenger over XMPP for the last handful of years before it was shut down using Pidgin and I'm pretty sure that's how it worked. You could talk to people on different networks but you needed your own FB account to talk on Messenger and you couldn't do group chats cross-network. GTalk and self-hosted XMPP could federate and you only needed one account and conversations could span servers.