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When you sign in to your account without selecting the "Keep me logged in" option (never use it on a shared computer or unknown location), Facebook will create a series of cookies set to automatically expire "at the end of the session": if you close the browser tab and don't use Facebook for an hour or two, going back to any page of the site later on will require you to log back in. If you check the checkbox to automatically sign in, you won't be asked to login for a full month. Regardless of how you login, you have full control over when the web browser "forgets" you - by manually signing out! Facebook even includes an option to remotely logout web browsers and mobile devices (an awesome setting in case you forgot to logout at work, school, the public library, or on any public computer to which you don't have access right now!)
Security Tip: you don't need to logout whenever you step away from your computer! Just quickly lock your machine with the keyboard shortcut that corresponds to your operating system:
• Windows (all versions) - hold down thekey and press L (as in "
Lock"!)
• Mac OS X - hit Cmd+Option+Eject or Cmd+Option+Power.
• Linux (most distributions) - press Ctrl+Alt+L (here too, remember "L" as in "Lock"!)
Quick Steps to sign out of your Facebook account:
If you check the option to automatically login to Facebook, a cookie is created for this particular web browser, instructing Facebook to bypass the sign-in form altogether. This cookie will remain active until it expires (exactly a month later), or until you manually clear your cookies. But manually signing out will delete that cookie.
To manually sign out, click on the dropdown arrow (top right corner of the page), and choose "Log Out" from the menu.
Within a second or two, you'll be redirected to the Facebook homepage, completely logged out. You'll see the blank login form at the top, and the sign up form in the bottom right corner. If you try to navigate to any profile page on Facebook, you'll be prompted to log back in (you can still see basic profiles, but cannot interact in any way with your account).
Note: if other tabs were opened to another page on Facebook.com in the same browser, they won't be closed. However, if you try to click on a link or button on any of these pages, or refresh them, you'll get the "Facebook Login" screen, asking you to log back in. To be safe (avoid having others using your computer be able to potentially see your account information, close all tabs!)
To sign out from the mobile version of the Facebook website (located at "m.facebook.com"), just click on the menu button in the top left corner of the page (it's a triple horizontal bar). Then, scroll all the way to the bottom of the list and tap on the "Log Out" link.
Depending on the web browser you are using on your phone or tablet, closing the browser tab once you've signed out is a good idea (for faster browsing speeds, some browsers "cache" the previous pages you visited, and reload them from a copy kept in memory - closing the tab ensures that no-one can use that feature to view pages after you've logged out!)
In the official Facebook app for iOS (iPhone, iPad, iPod touch - shown on screenshot) and Android (Kindle Fire, Nexus, etc.), tap on the "More" button in the lower right corner, scroll to the bottom, and tap on "Log Out".
Whenever you change your Facebook account password, you'll have the option of logging out all other web browsers and devices from your account once the new password takes effect: this is extremely useful if you suspect that someone else is using your account, or if you forgot to manually sign out of Facebook from a shared or public computer (but you can leave other devices logged in of course). 
While Facebook doesn't include an "automatic logout" option per se, remember that if you sign in without checking the "Keep me logged in" checkbox, you'll be automatically logged out within a couple of hours after you finished using Facebook - and that will happen whether the browser is currently running or not - just make sure to close Facebook browser tabs when you are done. There is also an extension for Chrome called "Facebook Auto Logout
" (shown on the screenshot), which allows you to set a timer: once the duration you chose elapses, you will automatically be logged out of Facebook. Unfortunately -or not, depending on how your goals- you cannot pause, cancel, or edit the timer once it has started. Even exiting and re-launching the browser won't work! You can download this extension from here. The very same add-on (also called "Facebook Auto Logout
") for Firefox is no longer available, for some reason.
Caution: to make pages load faster, and exactly as they were when you left them, some browsers will automatically restore the current login session in an inactive tab when you switch back to it - even if the browser was restarted in the meantime. Even if your browser doesn't do this, extensions you installed might have introduced that functionality. What means two things: if you want to make sure that you are logged out, click on the "Log Out" link in the dropdown (or remotely sign out that browser / device if you no longer have access to it).
Firefox has a fun extension whose sole purpose is to remove the "Log Out" option from the Settings menu. This is very useful if roommates or family members also using your computer keep signing you out whenever they check their own account! (A later tutorial will show you how to check multiple Facebook accounts from the same computer.) While using Firefox, you can install that extension from here. The only downside is that you have to disable the add-on if you actually want to log off Facebook! Unfortunately, neither Chrome nor Internet Explorer seem to have a similar add-on. This extension, by the way, is a simple explanation for the common "missing Logout button" problem!
Your Facebook login history keeps track of the most recent web browsers and devices that have logged into your account (or are still logged into it). You can manually force-logout any device from that screen: click on the dropdown arrow (top right corner of the screen), and select "Settings". In the next page, select "Security" on the left. The last section is labeled "Where you're logged in
": click on it to reveal the recent activity log.
Your login history is divided into device types: "Desktop
" (includes PCs, Macs, and laptops), "Facebook for Android
", "Facebook for iPad
", "Facebook for iPhone
", etc. Click on any white block to show a list of browsers or devices, with the date at which each of them logged into your account. To logout all devices, click on the corresponding "End Activity" link - this will terminate active sessions, but will not prevent signed-out devices from logging back in (see the "caution" note below). 
Force-logged-out devices are removed from your login history, and the count is updated: 
Session expired - please log in again" error message, just like the one on this iPhone app screenshot →
Even if you've signed out, there are two ways someone can log back in if they have access to your computer: by using the stored username and password saved inside your web browser, or by using a "password manager" you may have installed on your PC / Mac. We'll show you how to remove any traces from your login from the most popular web browsers. As you can tell from the screenshot, your login AutoComplete data remains even after logging out. For password managers, please check the documentation for that particular piece of software.
Here are the steps to erase your "remembered" login (Facebook or otherwise!) from Internet Explorer (Windows), Mozilla Firefox (Windows, Mac OS X, and Linux), and possibly in Google Chrome and Safari, depending on your operating system and the extensions you may have installed.
Double-click inside the "Email or Phone" field (where you normally type your username). Browsers will also show that list if you hit the Down arrow key on your keyboard, while the insertion point is blinking in the text field (typing the first letter works too!)
Tip: exiting a mobile Facebook app (e.g., the iPhone app) won't automatically sign you out. You can either remote-logout a device (see next section), or find the Logout function from within the mobile application (its location depends on the third-party app you are using - see the steps below for the official Facebook app).
Side info: this or similar extensions won't prevent you from signing out off Facebook, they'll just hide that button. If you cannot logout, check any JavaScript and/or cookies settings that may have changed in your browser since you last logged in. Also know that logging out only affects the current web browser: if you are signed in with other browsers (on this computer or another), make sure to manually logout from those as well (or use the remote logout option, discussed next!)
Caution: if any device you don't recognize is signed into your account, or has signed into it in the past, logging it out won't fix the problem. This means that someone was able to access your account, so you absolutely need to change your Facebook password - as soon as possible! The next time that tablet or smartphone loads the Facebook app, the user will see a "Delete key (Del). That email address or phone is has now been permanently forgotten by the web browser - if that browser had a password associated with that username, the password will be erased from the browser as well.Caveat: depending on your browser settings, logging into your Facebook account with that same username may "re-add" that combo to the remembered logins. To avoid that, disable auto-complete or the "remember password" feature from your web browser.