about is a URI scheme, implemented in various web browsers to reveal internal state and built-in functions. It is an IANA officially registered scheme, and is standardized.
The most commonly implemented about URIs are about:blank, which displays a blank HTML document, and simply about:, which may display information about the browser. Some browsers use URIs beginning with the name of the browser for similar purposes, and many about URIs will be translated into the appropriate URI if entered. Examples are opera (Opera) or chrome (Google Chrome). An exception is about:blank, which is not translated.
In early versions of Netscape, any URI beginning with about: that wasn't recognized as a built-in command would simply result in the text after the colon being displayed. Similarly, in early versions of Internet Explorer, about: followed by a string of HTML (e.g. about:<em>hello world</em>) would render that string as though it were the source of the page — thus providing a similar (though more limited) facility to the data: URI scheme defined by . Still other versions of Netscape would return various phrases in response to an unknown about URI, including "Whatchew talkin' 'bout, Willis?" (a catch phrase from the TV show Diff'rent Strokes) or "Homey don't play dat!" (from a recurring skit on the TV show In Living Color).
Standardization In 2010, and onwards, there are efforts to standardize the about URI scheme, and define the processing requirements for some specific URIs, in the IETF Applications Area Working Group (APPSAWG). In August 2012, it was published as an official Request for Comments as . The about URIs that have since been defined and assigned by IANA are listed below.
URIPurpose about:blankRFC 6694References a blank HTML document with the media type text/html and character encoding UTF-8. This is widely used to load blank pages into browsing contexts, such as iframes within HTML, which may then be modified by scripts. about:legacy-compatA reserved, though unresolvable, URI defined within HTML5 intended for use in the DOCTYPE designed for compatibility with some legacy authoring tools, such as XSLT, which may not be capable of outputting the more common, shorter alternative that lacks both the PUBLIC and SYSTEM identifiers. <!DOCTYPE html SYSTEM "about:legacy-compat">. about:srcdocA reserved, though unresolvable, URI defined within HTML5 intended to be the URI navigated to within iframes whose content comes from the srcdoc attribute. about:invalidReferences a non-existent document with a generic error condition. Intended for the case where a URL is necessary, but it should not be resolveable. about:html-kindUsed as an identifier for kinds of media tracks.
Common + Common "about:" URIsURIPurpose Firefox, SeaMonkey, Mozilla Google Chrome, Chromium Konqueror Opera Edge Internet Explorer about: Redirects to "chrome://version" Redirects to "about:konqueror" Redirects to "opera:about" Redirects to "edge://version" about:about Lists all the about: URLs (Firefox since version 4.0) Redirects to "chrome://about"; Lists all the chrome: URIs (Works like "chrome://chrome-urls") Redirects to "about:konqueror" Redirects to "opera:about" Redirects to "edge://edge-urls" about:blank Shows a blank document about:plugins Shows the filename, MIME type, description, suffix, and status of all installed plug-ins Shows the filename, MIME type, description, suffix, and status of all installed plug-ins Redirects to "opera:plugins" about:cache Shows information about the Cache Service. Redirects to "about:konqueror" Redirects to "opera:cache" about:mozilla Shows a page from the fictional Book of Mozilla. In some versions of Netscape, also replaced the meteors in the standard Netscape throbber with a large fire-breathing lizard. Redirects to "about:konqueror" Shows a blank HTML document with a blue background. Removed in Windows XP SP2. (The blue page can still be seen at "res://mshtml.dll/about.moz" instead.)
Chrome and Chromium derivatives The following applies to all web browsers that derive from the Chromium project, including Google Chrome, Microsoft Edge, Opera, and Vivaldi. + Chrome-specific "about:" URIs URI Purpose about:cache Deprecated in version 66 about:crash Crashes the current rendering process. (This causes the "Aw, snap!" crash notification page to be displayed.) about:credits Displays the list of free and open source software used in the browser, and their associated licenses. about:dino Displayed when the browser cannot connect to the target URL, this page contains an Easter Egg: Pressing the Space Bar key starts the _Dino_ minigame, which involves making a dinosaur jump over obstacles. Microsoft Edge doesn't feature this page, having replaced it with about:surf (see below.) about:dns Displays the DNS records about:flags Displays a page where experimental features can be configured by setting feature flags. about:gpu Displays information about WebGL and hardware accelerated graphics. about:histograms Displays histograms about:inducebrowsercrashforrealz Crashes the Google Chrome browser. This is designed for developers to test what happens when the Google Chrome browser crashes. Additionally, crashes Chromebooks entirely due to them running on Google Chrome. about:internets On particular versions of Windows, displays a page entitled "Don't Clog the Tubes!" which renders a page with an animation of the Microsoft Windows "3D Pipes" screensaver. Does not work on Windows Vista due to the pipes screen saver no longer being supported for releases after the 2.0.169.1 release. about:kill Same as about:crash, but with a violet background color and the message "He's Dead, Jim!" Occurs when the OS runs out of memory or the browser is killed by an external cause, such as the OS shutting down. about:labs Moved to about:flags in Chrome Dev channel 8.0.552.11 about:memory Displays the process manager about:net-internals Provides an interface for monitoring the network usage and performance statistics about:plugins Shows installed plug-ins (Deprecated in Chrome 57) about:sandbox Shows which sandbox protection mechanisms are currently enabled. about:shorthang Hangs the tab's process, making it become unresponsive. This is designed for testing the hanging protection. about:stats Displays statistics about processes. At the top of the page, it states "Shhh! This page is secret!" about:version Displays version information, same as about:
The above list is not exhaustive; for a full list, see about:about URI.
Firefox Many of these can also be used in Thunderbird, by setting them as the "Mail Start Page". Also, some extensions define additional about: URIs not listed here. + Mozilla-specific "about:" URIsURIsPurpose Firefox SeaMonkey, Mozilla Application Suite about:addons Shows installed addons, plugins, themes, and provides an interface for installing new addons (Firefox 4+ and SeaMonkey 2.1+) about:app-manager Shows the Firefox OS Simulator (Removed in Firefox 36) about:bloat Displays BloatView output (disabled in release builds). Superseded by about:memory on Gecko 1.9.2. about:bloat?new TBA about:bloat?clear TBA about:blocked Shows the malware protection page used when the browser identifies a page as not safe for viewing (Firefox 3+) about:buildconfig Shows the arguments and options used to compile the build in use about:cache Shows information about the Cache Service. Number of entries, location of cache, size of cache, etc. for both memory and disk cache. about:cache?device=memory Shows individual entries in memory about:cache?device=disk Shows individual entries on disk about:cache?device=offline Shows individual entries for offline viewing (Gecko 1.9+) about:cache-entry Shows information about a cache entry. Used in about:cache links. Requires parameters. about:certerror Shows the error page used when an SSL/TLS certificate is untrusted or otherwise invalid about:config Shows an interface for viewing and setting a wide variety of configuration variables, many of which are not otherwise accessible through the GUI (options panels).
The known earliest use of about:config dates back to Netscape 4.x, where it was not possible to edit the settings from the browser.
about:config settings first became modifiable in Mozilla Application Suite.
On first use, about:config displays a message which tells the user that the settings might void the warranty and they can be "Harmful to the stability, security, and performance of this application." The message about voiding one's warranty is a joke, as Mozilla Firefox ships without a warranty of any kind. The message has a checkbox to turn it off. about:crashes Shows details of crashes submitted by Mozilla's crash reporter (Firefox 3+, SeaMonkey 2.0+) about:credits Shows a list of all those who contributed to Mozilla about:devtools Shows the welcome page used by Firefox Developer Tools about:downloads Shows a list of downloaded files about:feeds Shows the page used when clicking the rss feed icon in the address bar about:healthreport Shows the Firefox Health Report about:home Shows the Firefox 4 default home page about:jetpack Shows an interface for viewing and setting the JetPack extension about:licence The equivalent of about:license in the British English localizations of Firefox. (See American and British English spelling differences). Not available since Firefox 4. about:license Shows the Mozilla Public License (and the Netscape Public License) for the piece of software (Gecko 1.8+) about:logo Shows the logo used on the about: screen about:memory Shows memory usage (Firefox 3.6+) about:mozilla Easter egg, shows a verse from The Book of Mozilla about:neterror Shows the error page used when the browser could not access the requested pathabout:newaddonThis URI is not registered. However, when the user tries to sideload an add-on, a dialog box bearing this URI appears. asking for the user's explicit consent. about:newtab Shows a grid of favourite and most-visited websites (Firefox 13+) about:permissionsShows permissions for all sites on Firefox 6.0a1 about:plugins Shows installed, currently enabled plug-ins about:preferences Shows the new preferences page about:profiles Shows the profile management page. about:privatebrowsing Can be used to switch to private browsing mode. It shows a message indicating that Firefox will not remember any history for the current session. Note: It does not show URI on the address bar about:reader?url= Opens the specified URL in Reader Mode. For example, about:reader?url=http://example.com. about:rights Shows licensing information about:robots Easter egg, beginning with March 8, 2008 trunk builds. The title of a window cites the iconic phrase of The Day the Earth Stood Still. The page's prose cites Isaac Asimov's first law of robotics. about:sessionrestore Shows an interface for viewing about last session. about:startpage In Ubuntu, shows the Ubuntu start page with the current search engine (if the "Ubuntu Firefox Modifications – ubufox" add-on is installed) about:support Shows troubleshooting information (Firefox 3.6+, SeaMonkey 2.1+) about:sync-tabs Shows list of tabs from other computers. Requires enabled synchronization.about:tabcrashed Contains the text displayed when a tab crashes. Added in Firefox 25. about:webrtc Shows an interface for WebRTC internals about:welcome Shows the welcome page used by Firefox
Opera (v1–15) In Opera, about: is an alias for the opera: scheme; therefore all these URIs also work with about prefixed. User JavaScript is disabled for all URIs in the about: or opera: schemes as a security feature. These pages can, however, be styled using local stylesheets.
Despite using an Opera derivative, the Nintendo DS Browser does not support any of the following functions; the Nintendo DSi Browser, however, does support opera:about.