about URI scheme

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"about:blank" redirects here. For the spyware variant “aboutblank”, see CoolWebSearch § Variants.


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.

In early versions of Netscape, any URI beginning 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).[1][2]

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. Opera uses URIs beginning with opera for similar purposes, and many about URIs will be translated into an appropriate opera URI if entered; an exception is about:blank, which is not translated.

Note: In more recent versions of Internet Explorer, many of the following do nothing or have since been removed.

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).[3] In August 2012, it was published as an official Request for Comments as RFC 6694. Note that Opera ASA, the proponents, had long used and advocated alternative browser specific URIs.[4] The about URIs that are known to be defined for specific purposes are listed below.

URI Purpose
about:blank[5] Returns 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-compat A 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: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 A reserved, though unresolvable, URI defined within CSS Values and Units module, intended as a non-existent document with a generic error condition for use where a URI is necessary, but where no actual resource is desired.

Common about: URIs

Common about: URIs
URIs Mozilla / SeaMonkey Mozilla Firefox Google Chrome Chromium Konqueror Opera Safari Internet Explorer / Edge MSN Explorer
about: Shows version information and copyright information Translated to “chrome://version” Translated to “about:konqueror” Translated to “opera:about” Shows a blank page
about:about Lists all the about: URIs
(Firefox since version 4.0)		 Translated to “chrome://about”
Lists all the chrome: URIs
Works like “chrome://chrome-urls”		 Translated to “about:konqueror” Translated to “opera:about” Shows nothing but the text:“about”
about:blank[note 1] Shows a blank document
about:plugins Shows the filename, MIME type, description, suffix, and status of all installed plug-ins Translates to “chrome://plugins/”, works like Chrome Shows the filename, MIME type, description, suffix, and status of all installed plug-ins Translated to “opera:plugins”
about:cache Shows information about the Cache Service. Lists the URIs of pages stored within the cache, with each linking to view-cache:uri that provides more information about its content. Translated to “chrome://cache”, works like Chrome Translated to “about:konqueror” Translated 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. Translated to “about:konqueror” The Windows version of IE showed a blank HTML document with blue background color. Possibly a joke reference to the “Blue Screen of Death”. Removed in Windows XP SP2 but it can still be shown by typing “res://mshtml.dll/about.moz” instead.

Mozilla-specific about: URIs

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.[6]

Mozilla-specific about: URIs
URIs Mozilla Application Suite / SeaMonkey Mozilla Firefox
about:addons Shows installed addons, plugins, themes, and provides an interface for installing new addons. Firefox 4+, 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.[7]
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). It 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.[8]
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:downloads Shows a list of files you downloaded.
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 In the British English localised version, shows the content of about:license but with all occurrences of license used as a noun replaced with licence (see American and British English spelling differences). Not available in 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:newtab Shows a grid of your favorite 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:rights Shows licensing information.
about:robots Easter egg, beginning with March 8, 2008 trunk builds. The title of a window contains a citation from The Day the Earth Stood Still.[9]
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 addon Ubuntu Firefox Modifications – ubufox 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:webrtc Shows an interface for WebRTC internals.

Opera (Presto)-specific about: URIs

about is an alias for opera; therefore all these URIs also work with about prefixed. User JavaScript is disabled for all URIs in the about or opera URI schemes as a security feature. These pages can, however, be styled using local stylesheets.

None of these functions, except the opera:about combination, work in the Nintendo DS version of the Opera browser, the Nintendo DS Browser.

Opera-specific about: URIs
URIs Opera
opera:blank Maps to about:blank
opera:about Provides info about the browser and the configured paths.
about:opera Maps to opera:about
opera:cache Shows the content of the cache.
opera:config (Opera 9.0 and newer) Shows a page that allows changing of numerous browser preferences, many of which cannot be accessed through the normal Preferences window
opera:drives (Operating system specific) Shows the local drives of the host system.
opera:history Shows the content of the browser history.
opera:historysearch (Opera 9.5 and newer) Shows the start page of internal search engine for the browser history.
opera:plugins Shows installed plug-ins. Opera 11 and newer allow you to disable individual plug-ins from this page.
opera:button Defines a custom button as a set of Opera actions. (Note: This does not work directly, you need to specify all button parameters as on CustomButtons.)
opera:help Shortcut to the help directory. This can be either local or external.
opera:debug (Opera 9.5 and newer) Shows a page that allows changing of settings for remote debug of Opera via Opera Dragonfly
opera:memdebug (Opera 9.5 and newer) Shows debug information about memory usage.
opera:webstorage (Opera 10.5 and newer) Shows information Web Storage (see HTML5).
opera:webdatabases (Opera 10.5 and newer) Shows information Web Storage databases (see HTML5).
opera:gpu Shows information about hardware accelerated graphics and GPU support.
opera:cpu (Introduced in Opera 12 beta). Displays CPU usage.

Internet Explorer-specific about: URIs

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.

Note: Any about URI that is not recognized by Internet Explorer redirects to a page saying "Navigation to the webpage was canceled"

URI Internet Explorer 6 (SP2) Internet Explorer 7 Internet Explorer 8 Internet Explorer 9-11
about:home Displays the user's home page. No longer supported. Displays the user's home page.
about:blank Displays the blank page.
about:desktopitemnavigationfailure Displays “navigation cancelled” page. No longer supported.
about:navigationcanceled Displays “navigation cancelled” page. No longer supported.
about:navigationfailure Displays “navigation cancelled” page. No longer supported.
about:noadd-ons Displays information page when add-ons are disabled.
about:noadd-onsinfo Displays information page about the effects when you use add-ons.
about:offlineinformation Informs the user that the current page can not be viewed off line. No longer supported.
about:postnotcached Informs the user that the current page needs to refresh and any information entered in a form will have to be re-posted. The page has the title: "Webpage has expired"
about:securityrisk Informs the user not to browse with the current security settings because they may be harmful to the computer.
about:tabs Informs the user about tabbed browsing. It is also loaded when a new tab is created if the “Open home page for new tabs instead of a blank page” setting is enabled
about:inprivate Informs the user about InPrivate Browsing. It is loaded when InPrivate Browsing is initiated.

Edge-specific about: URIs

URI Microsoft Edge
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 a news-feed based on articles from MSN

Note: Any “about:” URI is accepted, but only returns a page with the message “Well, that didn’t work”.

Chromium-specific about: URIs

URI[10] Google Chrome
about:cache Shows the content of the cache.
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:dns Displays the DNS records
about:flags See about:labs
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.
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 Displays a page for testing features. 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.
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:

Note: Any “about:” URI is accepted, but only a page with a blank source is returned, as with the “about:blank” of other browsers. Similar to Safari.

Note: In Chromium “about:” is usually translated to a “chrome://” URL.

Konqueror

Note: Any about URI except about:blank and about:plugins redirects to about:konqueror.

URI Konqueror
about:konqueror Shows a friendly ‘start’ and navigation page

Epiphany

Lua error in package.lua at line 80: module 'strict' not found. Note: When Epiphany used Gecko as its layout engine, the general and Mozilla-specific about: URIs worked as in Mozilla Firefox. Since WebKit became Epiphany's layout engine, only these URIs are supported:[citation needed]

URI Epiphany
about:blank Displays the blank page.
about:plugins Shows installed plug-ins.
about:epiphany Displays the following message:[11] <templatestyles src="Template:Blockquote/styles.css" />

   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.[note 2]   

— Antoine de Saint-Exupéry   
about:applications interface for managing web applications, supported since release 3.2, to be removed in release 3.4.[12]

Netscape (historical)

  • 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.[13]
  • 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).[14]
  • 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.[15]
  • Some versions of Netscape would display the browser history for the about:global URI[15]

Internet Explorer for Mac OS 5 (historical)

In Internet Explorer for Mac 5 was an offline Easter egg, accessible by typing ‘about:tasman’, showing the Acid1 test with the text replaced by the names of the developers.[16]

Safari

Any about URI is accepted, but only a page with a blank source is returned, as with the about:blank of other browsers.

Microsoft Outlook

In Microsoft Outlook, an additional outlook:today URI was added, which showed the Outlook Today Screen (it shows messages, tasks and appointments and is also accessible from IE). Also, although about:blank is supported, anything else (including about:about) typed after about: would show that text as a web page in the browser.

Notes

  1. ↑ The term “about:blank” is also the generic name for a group of variants of the CoolWebSearch malware program group.
  2. ↑ It seems that perfection is attained not when there remains nothing to add, but when there remains nothing to remove.

References

  1. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ RFC 6694
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ 15.0 15.1 Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.

External links

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