Firefox Sanitize on Shutdown: Dialog and Wiped Data Types

This article provides a comprehensive overview of the "Sanitize on Shutdown" dialog in the Mozilla Firefox web browser. It explains the purpose of this built-in privacy feature, how it functions when you close the browser, and details the exact types of user data and history that can be selectively wiped automatically.

What is the Sanitize on Shutdown Dialog?

The "Sanitize on Shutdown" dialog—officially labeled in the modern Firefox user interface as the Settings for Clearing History dialog—is a privacy configuration tool. It allows users to dictate exactly what information Firefox should automatically erase every time the browser is closed.

Instead of manually clearing your history or constantly using Private Browsing mode, this feature lets you browse normally while ensuring your digital footprint is wiped clean at the end of every session. You can access this dialog by navigating to Firefox's Settings, selecting the Privacy & Security panel, scrolling to the History section, setting Firefox to "Use custom settings for history," checking the box for "Clear history when Firefox closes," and clicking the Settings... button next to it.

Data Types You Can Selectively Wipe

The dialog divides your personal information into two main categories: History and Data. You can toggle checkboxes next to the following specific data types to customize what gets deleted upon shutdown:

History

  • Browsing & Download History: Wipes the list of websites you have visited and the record of files you have downloaded. (Note: This does not delete the actual downloaded files from your computer's hard drive).
  • Active Logins: Clears any logins to websites that use HTTP authentication you have entered during your current session.
  • Form & Search History: Deletes text you have entered into website forms (like names, emails, or addresses for autofill) and queries you have typed into the Firefox search bar.

Data

  • Cookies: Erases small files stored on your computer by websites used to remember your login status, site preferences, and tracking status. Firefox allows you to set exceptions in the main privacy menu if you want to keep cookies for specific trusted websites while wiping the rest on shutdown.
  • Cache: Deletes temporary files, such as images, scripts, and web page parts, that Firefox saves to your computer to make previously visited websites load faster.
  • Site Settings: Resets website-specific permissions you have granted, such as allowing a site to use your camera, microphone, location, or send you pop-up notifications. It also clears custom zoom levels and character encoding preferences.
  • Offline Website Data: Removes large files stored by websites on your device that allow those web applications to function even when you are not connected to the internet.

Once you check the boxes for the desired data types and click OK (or Save Changes), Firefox will silently and automatically execute this sanitization process every time you quit the application.