Follow The Steps
Step 1 Look for Bookmarks on the top navigation. Select
Organize Bookmarks…
Step 2 Click New Bookmark... tab and enter the following:
* Name: Facebook Chat
* Location: http://www.facebook.com /presence/popout.php
* Check Load this bookmark in sidebar.
Step 3 Launch the Firefox sidebar, click Facebook Chat and
start chatting with your Facebook contacts within
Firefox.
That's it! Enjoy