There is a lot of useful information about Firefox hidden away behind the about: URL protocol. The most useful is the URL about:config, which displays preferences and settings that can be inspected and changed.

Available about: URLs depend on your specific Firefox version. Here is a complete list of URLs in the about: pseudo protocol:

about: page Description
about: Displays version and build information and links to the contributors, licensing information and build configuration
about:about Provides an overview of all about: pages available for your current Firefox version
about:accounts Page used by the Sync feature
about:addons Add-ons Manager
about:app-manager App Manager
about:buildconfig Displays the configuration and platform used to build Firefox
about:cache Displays information about the memory, disk, and appcache
about:checkerboard Switches to the checkerboarding measurement page, which allows to detect checkerboarding issues
about:compartments Displayed information about compartments; since Firefox 26, that information can be found in the "Other Measurements" section of about:memory.
about:config Provides a way to inspect and change Firefox preferences and settings
about:crashes Lists all crashes, which happened during the runtime of Firefox (in case the user enabled the crash reporter)
about:credits Lists all contributors to the Firefox project
about:customizing Switches to the customization page, which allows to customize Firefox' UI
about:debugging Switches to the Developer Tools debugging page, which allows you to debug add-ons, tabs and Service Workers
about:downloads Displays all downloads done within Firefox
about:healthreport Displays performance information of Firefox (in case the user enabled the health report)
about:home Start page of Firefox when opening a new window
about:license Displays licensing information
about:logo Firefox logo
about:memory Provides a way to display memory usage, save it as report and run the GC and CC
about:mozilla Special page showing a message from "The Book of Mozilla"
about:networking Displays networking information
about:newtab Start page when opening a new tab
about:performance Displays memory and performance information about Firefox subprocesses/add-ons/tabs
about:plugins Displays information about installed plugins
about:preferences Firefox settings (also available through Firefox menu > Options)
about:privatebrowsing Start page when opening a private window
about:profiles Display and manage Firefox profiles
about:reader Indicates a web page has Firefox Reader View turned on. See Firefox Reader View for clutter-free web pages
about:rights Displays rights information
about:robots Special page showing notes about robots
about:serviceworkers Displays currently running Service Workers
about:sessionrestore Session restoration (displayed after a Firefox crash)
about:support Troubleshooting information (also available through Firefox menu > ? (question mark) > Troubleshooting Information)
about:sync-log Displays a synchronization protocol related to the Sync feature
about:sync-progress Page displayed after the Sync feature got set up
about:sync-tabs Lists tabs available for synchronization related to the Sync feature
about:telemetry Displays telemetry data collected and sent to Mozilla while Firefox is running (in case the user enabled telemetry)
about:webrtc Information about WebRTC usage
about:welcomeback Information page displayed after Firefox is reset

These URLs are defined in docshell/base/nsAboutRedirector.cpp within the kRedirMap array.  The array maps most of the URLs, like config to URLs in the chrome: pseudo protocol, such as chrome://global/content/config.xul.  The about location information is duplicated in docshell/build/nsDocShellModule.cpp.

Note: You must access about: protocol pages by typing them into the address bar. Attempts to navigate through window.location will throw —  Error: Access to 'about:addons' from script denied.

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Last updated by: noritersand,