Adium already has a built-in support for Facebook Chat. You may add Facebook Chat to Pidgin as generic XMPP service.
To configure your jabber client use the following recommended settings:
Protocol: XMPP or Jabber
Username:
Domain: chat.facebook.com
Jabber ID: @chat.facebook.com
Password:
Enter the following server info, as requested:
Port: 5222
Server: chat.facebook.com
Use SSL/TLS: no
Allow Plaintext Authentication: no
When you connect to Facebook account you'll see your Facebook friend groups in roster.
Friend groups (friend lists) can be edited only from Facebook site, not from the XMPP client.
Only your confirmed friends can contact you through Facebook Chat.
Currently, Facebook Chat does not support SSL and message encryption, but supports secured authentication using MD5.
For information about integraitng with Facebook Chat see here.