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Internal URI scheme
about is an internal URI scheme (also known as a "URL scheme" or, erroneously, "protocol") implemented in various web browsers to reveal internal state and built-in functions. It is an IANA officially registered scheme, and is standardized.[1]
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 RFC 2397. 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).[2][3]
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).[4] In August 2012, it was published as an official Request for Comments as RFC 6694. The about URIs that have since been defined and assigned by IANA are listed below.[5]
<!DOCTYPE html SYSTEM "about:legacy-compat">. about:srcdoc A reserved, though unresolvable, URI defined within HTML5 intended to be the URI navigated to within iframes whose content comes from the srcdoc attribute. about:invalid References a non-existent document with a generic error condition. Intended for the case where a URL is necessary, but it should not be resolveable.[7] about:html-kind Used as an identifier for kinds of media tracks.[8] Common "about:" URIs URI Purpose Firefox, SeaMonkey, Mozilla Google Chrome, Chromium Konqueror Opera Edge Internet Explorer about: Deprecated in Firefox 57 (Firefox Quantum) Redirects to "chrome://version" Redirects to "about:konqueror" Redirects to "opera:about" Redirects to "edge://version" — about:about Lists all the about: URLs
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[11] Purpose about:cache Deprecated in version 66[10] 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 withabout:surf (see below.)[12] 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)[9] 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.
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.[13]
Mozilla-specific "about:" URIs URIs Purpose 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 — about:bloat Displays BloatView output (disabled in release builds). Superseded by about:memory on Gecko 1.9.2.[14] — 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.[15] 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 path about:newaddon This 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:permissions Shows permissions for all sites on Firefox 6.0a1 — about:plugins Shows installed, currently enabled plug-ins about:preferences Shows the new preferences 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.[16] 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
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.
Internet Explorer about URIs are configurable in Windows. It is therefore possible that some of the listed URIs will not work on a particular computer. For example, "about:mozilla" was removed in SP2 (although the page can still be found at "res://mshtml.dll/about.moz"). These about URIs are sometimes used for spyware and adware, most notably in CoolWebSearch, which made about:blank display advertisements.
Any about URI that is not recognized by Internet Explorer redirects to a page saying "Navigation to the webpage was canceled."
The following applies to Microsoft Edge Legacy version 20 through 44. For newer Edge versions, see the Chromium section.
Microsoft Edge Legacy-specific "about:" URIs URI Purpose about:home Shows the content that would be shown if the home button were pressed about:flags Displays a list of Developer Setting and Experimental features about:start Shows the customizable (default) start page. about:config Redirects to about:flags about:tabs Shows the (default) new tab page. about:compat Shows the Enterprise Mode list (if configured) about:edge Shows the Edge logo. about:inprivate Shows the inprivate information tab. about:surf A surfing game easter egg.When GNOME Web (formerly Epiphany) used Gecko as its layout engine, all Firefox-specific about: URIs worked in it. After the adoption of WebKit as its layout engine, only the following URIs are supported.[citation needed]
Il semble que la perfection soit atteinte non quand il n'y a plus rien à ajouter, mais quand il n'y a plus rien à retrancher.
It seems that perfection is attained not when there remains nothing to add, but when there remains nothing to remove.
—
Antoine de Saint-Exupéry
It is a quote from Chapter 3 of Saint-Exupéry's memoir Terre des Hommes (titled Wind, Sand and Stars in its English translation by Lewis Galantiere).
about:applications Interface for managing the Web Application Mode, supported since release 3.2.[19] about:overview Displays a grid of thumbnails for the more visited websites. about:gpu Displays information about WebGL and hardware accelerated graphics. about:web Displays the browser and its engine information, same as about: about:incognito Displays information about incognito mode. Is a blank page in non-incognito mode.The about: URL originated in and has existed in all versions of Netscape browsers. It was originally added as an Easter egg to display information about the development team.[20]
Older versions of the Netscape browser have an about:people URI that was similar to about:credits above, but it would redirect to Netscape's active employee listing. In addition, about:username, where username is the username of a Netscape employee, would redirect to the Netscape homepage of the employee specified. For example, about:jwz would redirect to http://people.netscape.com/jwz/ (not an active link).[21] Not all employee pages were accessible through this scheme. Only developers who knew which file in the source tree and the encoding scheme used to obfuscate the directory of employee about entries could add their names.[citation needed]
Many other about: easter eggs existed, including the famous about:mozilla, and other less known ones that showed pictures of the Netscape mascot Mozilla in various foreign garb, such as about:deutsch showing Mozilla in Lederhosen.[22]
Some versions of Netscape would display the browser history for the about:global URI.[22]
about URI except about:blank and about:plugins redirects to about:konqueror, which shows a friendly ‘start’ and navigation page.about:blank.outlook:today URI, which shows the Outlook Today Screen. This screen shows messages, tasks and appointments; it is also accessible from Internet Explorer. Outlook recognizes about:blank too, but no other "about:" URIs.RetroSearch is an open source project built by @garambo | Open a GitHub Issue
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