By default, the self-logout time is 60 seconds. However, you can change back to another time as you like. To do so, type about: config in Address bar to Firefox, click I'll be careful, I promise! If the message appears. Next, type extensions.fbautologout into the Filter box to make two settings for Facebook Auto-Logout appear. You double-click on extensions.fbautologout.delay line and then type the number of seconds to logout automatically into the Enter interger value dialog box, click OK . To not show the notification in the corner of the screen every time you log out of Facebook, double-click the extensions.fbautologout.notify line to convert the value in the Value column from true to false .
Download the Facebook Auto-Logout utility for Firefox here .