This video will show you how to connect Facebook Messenger to Pidgin IM by installing third party plugins. This particular video will show you how to install to the portable apps version although desktop users can follow along as well. Facebook has apparently dropped XMPP support so this is a verified work around.
Pidgin
http://www.pidgin.im/
Jgeboski's GitHub (Plugin Download)
https://github.com/jgeboski/purple-facebook/wiki/Installing-on-Windows
Facebook Username
https://www.facebook.com/username
