HOW TO ADD FACEBOOK CHAT ON FIREFOX SIDEBAR:

Look for Bookmarks on the top navigation. Select Organize Bookmarks…
STEP:1

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.