Well, I might be very late in this topic. There are thousands of articles in the web regarding this issue. But why I'm re posting this because most of them are too tough to understand and devoid of screen shots. Here is the simplest method to get old facebook chat tool back. Then, let's move on. I have the trick for both google chrome and mozilla firefox.



In Google Chrome, its really easy task to install the script to
enable the Old facebook chat. Just Click the Following link to install
Script. CLICK HERE TO GO TO DOWNLOAD SCRIPT PAGE. In the Script page Click ‘INSTALL’ button which is in the Top Right side of the page.





Now the Install Popup will appear, in that box CLICK ‘INSTALL’ and now the Script is Installed.





Now the Script is Installed. Now Close the Existing Facebook page and
Open the Facebook again. You can See your Old Favorite Chat is
available. If you cant see the old facebook chat, Clear the cache and
open the facebook. Anytime you can remove this script from extension
menu of the Google chrome to get the New sidebar chat box.

How to Install Old Facebook Chat Script in Mozilla Firefox

In Mozilla Firefox, First we need to install Grease Monkey Add-on
before installing the Old Facebook Script. So Open the Firefox and go to
Download page of the Grease Moneky Add-on from the following link. Click here to go to Gease Monkey Add-on Download page. In the Download page Click ‘Add To Firefox’ button.