since libpurple doesn't support facebook chat anymore, the only alternative (apart from going to www.messenger.com in your browser) is now bitlbee with custom-built https://github.com/jgeboski/bitlbee-facebook (using the mobile facebook-api) and the stand-alone client https://github.com/Aluxian/Facebook-Messenger-Desktop which is a wrapper for a html-viewer opening that www.messenger.com, packaged up for debian. (something similar to the latter is also available for internet-explorer11 at http://www.neowin.net/forum/topic/1253174-messenger-the-windows-desktop-messenger-client/ where you probably can request the c# sourcecode -- if you want to create your own version or compare sourcecode for checking copyrights.)
Created attachment 418562 [details]
Bitlbee-facebook does not have an official release yet. I attached an ebuild that builds the plugin from github repository. It works for me with bitlbee-3.4.1 version.
Created attachment 423212 [details]
The first release of bitlbee-facebook is out. This is an ebuild for it.
Created attachment 427544 [details]
CCing bitlbee maintainers, are you interested in maintaining this package?
otherwise, I will proxy-maintain it.
also CCing upstream FYI, no action is required (unless you also want to proxy-maintain)
Go for it!
Created attachment 431728 [details, diff]
Created attachment 446426 [details, diff]
fix upstream metadata, Manifest
The bug has been closed via the following commit(s):
Author: Petr Vaněk <email@example.com>
AuthorDate: 2017-11-17 17:06:02 +0000
Commit: David Seifert <firstname.lastname@example.org>
CommitDate: 2017-11-17 18:38:44 +0000
net-im/bitlbee-facebook: New ebuild
Package-Manager: Portage-2.3.13, Repoman-2.3.3
net-im/bitlbee-facebook/Manifest | 1 +
.../bitlbee-facebook/bitlbee-facebook-1.1.2.ebuild | 38 ++++++++++++++++++++++
.../bitlbee-facebook/bitlbee-facebook-9999.ebuild | 38 ++++++++++++++++++++++
net-im/bitlbee-facebook/metadata.xml | 24 ++++++++++++++
4 files changed, 101 insertions(+)