Our latest 1.4 release allows you to do that:
Yo Dawg, I herd you like secure messengers, so I put a secure messenger in your secure messenger so you can message securely while you message securely.
I briefly thought that this was a demo of briar tunneling via facebook messenger / WhatsApp. Now I'm a little bit disappointed.
(In many countries, Facebook has deals with mobile providers that makes access to only their services significantly cheaper than Internet access, so if someone can come up with a way to use it for secure messaging, that'd be really helpful.)
Fosstodon is an English speaking Mastodon instance that is open to anyone who is interested in technology; particularly free & open source software.