Hi, I don't know about the others, but at the moment I have no way to use Facebook messages on UT.
And what about creating an app based on libpurple libraries?
It had occurred to me before, but I knew it would be a lot of work.
Something like this:
https://github.com/Michal-Szczepaniak/Morsender
Libpurple can do a lot of protocols, including Facebook:
https://developer.pidgin.im/wiki/ThirdPartyPlugins