As of Thunderbird 15, Thunderbird supports instant messaging and chat using IRC, Facebook, XMPP, Twitter, and Google Talk.
To use Chat, you must first create a new account (or configure an existing account) with an online instant messaging or chat provider. Thunderbird currently works with IRC, Facebook, XMPP, Twitter, and Google Talk.
In this example we will show IRC, but the process is very similar for Facebook, Twitter, Google Talk and XMPP.
At the top of the Thunderbird window, click on the File menu, then click New and then click Chat Account…:
For IRC, you will have to enter your IRC server name, e.g. irc.mozilla.org for Mozilla's IRC server.
For XMPP, you will also have to enter your XMPP server name.
For Facebook, your username can be found at: https://www.facebook.com/username/
Enter the password for the service.
This is not usually needed, so just click NextContinue.
Next, you will be presented with a Summary screen. Click Finish to finish the wizard and start chatting.
First make sure that you are online by going to your Chat Status and connecting:
Click on the Chat Tab next to the Write Tab to start and join conversations.
Like any other type of Thunderbird account (e.g. email and RSS), Chat is integrated with search.
Here's an example of email, Twitter, Facebook and Chat conversations being found by Thunderbird's global search: