There are two apps for Mozilla, Opera and for Chrome that does the magic. I will recommend that you try both of them and see which one you like the most.
Recover Old FaceBook Chat:
This add-on will replace the new social chat window with the older one. You can download the Chrome extension by clicking here
Facebook Chat Sidebar Disabler:
This add-on performs the exact same operation but with a different style. This one works for smart phones like IPhone or android because it has an Opera version. After installing the add-on in order to toggle between old-style chat and new-style chat, use the Options menu in the buddy list.
Click here To Download the Opera Version
Click here To Download the Chrome Extension
