1. Make sure you are running Firefox 17. You can check your version of Firefox in the “About Firefox” section.
  2. In your Firefox browser, go to this link: https://www.facebook.com/about/messenger-for-firefox. Click the “Turn On” button (You will have to login to your Facebook account).

That’s it. You should see a few Facebook icons appearing at your menu bar and the sidebar will appear with your Facebook friends.

Turning the Facebook messenger off

To turn it off, simply click the “Facebook” icon and select “Remove from Firefox”.

Enjoy!