How do I set up my Facebook account in Pidgin?

You need facebook username to use with pidgin as well as empathy. Select protocol to facebook in pidgin add account

On username section enter just username i.e. facebook.com/USERNAME will take you to your facebook public page. If you don't have one you should get it.

Facebook has stopped this service for more see: http://www.omgubuntu.co.uk/2015/04/facebook-chat-api-empathy-pidgin-stop-working

For those of you who want to use Facebook Chat in Pidgin, there's a new plugin which makes this possible, called purple-facebook For more information see this: http://www.webupd8.org/2015/08/use-facebook-chat-in-pidgin-with-purple.html

I can confirm this also, I went to my facebook page and went into General account settings and found the user name that facebook assigns. It is the long line with the http:// the only thing you need is the part where it has your name in it towards the end. I copy and pasted that into the part in pidgin where it ask for the user name and applied. Whola working pidgin that shows facebook im contacts. Hope this helps someone... Peace....

Adapted from @vasandharaj's link, to be persisted here, because it simply works, although FB announced the end of xmpp support by 30th of April 2015 (pidgin-im.de, german) and now it's the 6th of May 2015 and I connected right now for the first time.

Setup Facebook Chat in Pidgin (using Jabber/XMPP)

1. In Pidgin go to "Accounts" and select "Manage Accounts". On the Basic tab enter the following info:

• Protocol: XMPP
• Username: [your Facebook username, check your account setting for your profile URL]
• Domain: chat.facebook.com
• Resource: Pidgin
• Password: [your Facebook password]
• Local alias: [your name]

2. Click the Advanced tab, enter the following info:

• Connection Security: encrypt connection if available.
• Connect port: 5222
• Connect server: chat.facebook.com

Ok, that's it. You can chat with your friends with Pidgin-IM.