Open Pidgin (after installing of course; you can install Pidgin from the Ubuntu Software Center), and go to the Add accounts option (Accounts > Manage Accounts > Add). Now, select the protocol as XMPP, enter your username (mind you this is the username and not the email address), enter the password and select the domain as chat.facebook.com
Next, select the Advanced tab and disable the Require SSL/TLS option. Click on Add to finally activate it.
Thats it, if you're using Pidgin and want to use it as your preferred application. You may not read the rest of the post.
If however you're using Empathy, then keep reading.
After configuring Pidgin, the next time you launch Empathy, you will get a notification similar to this:
Now, simply click on the first option, i.e. Import my accounts details from Pidgin. And then select the accounts you want to import (just follow the on-screen instructions). And thats it.
(Of course adding the other accounts like google talk etc. is very easy on both Pidgin and Empathy. Just a bit of info though, this Empathy configuring which you needed to do, isnt needed at all in 10.04. The version of Empathy in 10.04 already has an option of adding account specifically for facebook.)
(Tip: If you dont get the notification from Empathy about importing accounts, remove all existing accounts from Empathy. The quit and restart Emapthy)
