Everybody has a Facebook account these days and they share their personal life with their friends and family on it – including events, pictures and videos. When you login to your Facebook account in Firefox (or any browser), you stay logged in for multiple sessions until you manually logout. If you forget to logout, then your account can be used by someone you share your computer with. To prevent this, you should always log out of your Facebook account each time after using it. But if you are a Firefox user, then you can set it to automatically log out of your Facebook account using the Facebook Auto-Logout add-on.
The Facebook Auto-Logout add-on logs you automatically out of Facebook when you close Firefox or if you have not opened Facebook for a specified period of time – default time being one minute. This add-on removes all Facebook cookies, resulting in your automatic logout. This also makes your Facebook presence hidden from other sites which use the Facebook like button. Because your Facebook cookies are removed, they cannot trace your web browsing behavior using these tracking cookies.
You can download this add-on from the Mozilla Firefox website. The add-on does not require you to restart your Firefox browser. After the add-on is installed, you can open the Add-ons Manager by selecting Tools → Add-ons from the menubar. Alternatively, you can also use the keyboard shortcut Ctrl + Shift + A to open it. Here you can configure the settings for the Facebook Auto-Logout add-on.
In the settings, you can choose automatic updates for this add-on, whether to show notification of logging out from Facebook and the time period (in seconds) of inactivity on your Facebook page after which it would automatically log you out. By default, this inactivity period is 60 seconds, but you can increase it to a suitable value based on your preference. I have set this value to be 6000 seconds (or 10 minutes).
Now you can open Facebook in Firefox browser and login to your account. If you close the Facebook tab, then after the pre-specified time period of inactivity you would be automatically logged out. You would see a notification pop-up in the bottom-right corner of Firefox window as shown.
Although you can manually logout from Facebook each and every time to prevent any inadvertent access to your Facebook account by someone else, yet it is a much safer to set Firefox to automatically log you out. This way you know that you would be logged out as soon as you close the browser, even if you forget to logout. You can download and install this add-on from https://addons.mozilla.org/.