Facebook Chat is not working in Empathy and other third-party desktop instant messaging client such as Pidgin starting from April 30 2015. This is prior to XMPP API from Facebook is turned off. As you may know, Facebook is using custom XMPP API to develope their Facebook Chat feature until it upgraded to their own product. Altough it is still not clear, the new replacement for XMPP API is not announced. For you that use pidgin or empathy and need to get desktop support for Facebook Chat, you can just logged in to facebook website and start using their messaging service directly via web. Or, if you're using smartphone, you can use "Facebook Messenger" app. All that is being lost is the ability to chat to them through unofficial apps such as Empathy, Pidgin and Kopete.