I like Mattermost client, it's way better than anything else out there.
I want to manage my Facebook messages inside Mattermost client, and I want to connect to an IRC which has nothing to do with my corporation.

So I want to mess my private life with work, but I would be very happy about this.

There were trials, for example, libpurple with Pidgin chat client. But Pidgin is like using windows live messenger in 2020.

I know Facebook Messenger has no public protocol for that, so I'm not requesting to implement that, but provide, for example, IRC, libpurple protocols to let community hack facebook into Mattermost.