Facebook made their ‘Facebook chat’ protocol all awesome and nice today by adding support for the Jabber/XMPP protocol. This means you can have facebook chat in Pidgin, Empathy, etc without the need for buggy third-party plugins! Hoorah!
In theory the same steps should work on Empathy.
Osliner posted the following steps for Empathy in the comments: -
Login ID: firstname.lastname@example.org
No encryption, and everything else is empty or default.
Make sure when you click “Add” in Empathy, that you then select “Reuse existing account” (Thanks to Karl)