Facebook Chat is very essential in most users of Facebook. They can interact with each other easily and communicate with their friends in real-time. But recently Facebook had changed their chat system by replacing the chat bar with sidebar. This sidebar doesn't show all your online friends but only those people you often communicate with are the only visible which is very very annoying plus the big part of the page occupied by that sidebar... After couple of hours in searching, I found these wonderful add-ons and extensions that can help you revert to old chat of Facebook. Just download and install one of these add-ons or extensions according to your browser and refresh your Facebook.
For Firefox users, download this add-on.
For Chrome users, download this extension.
For Opera users, download this add-on.
-Source
Note: This is not a Greasemonkey script like the others
