View source for About URI scheme

{{short description|Internal URI scheme}}
{{lowercase title}}
{{Multiple issues|{{more citations needed|date=September 2010||talk=}}
{{Overly detailed|date=March 2021}}
{{Update|date=May 2021}}}}
<!-- Note to editors — matching the empty style string for inline with "|=" is important!-->

'''about''' is an internal [[URI scheme]] (also known as a "[[Uniform Resource Locator|URL]] scheme" or, erroneously, "[[protocol (computing)|protocol]]") implemented in various [[web browser]]s to reveal internal state and built-in functions. It is an IANA [[URI scheme#scheme|officially registered scheme]], and is standardized.<ref>{{cite web|url=https://www.iana.org/assignments/uri-schemes/uri-schemes.xhtml|title=Uniform Resource Identifier (URI) Schemes|website=www.iana.org|access-date=2016-09-28}}</ref>

The most commonly implemented <code>about</code> URIs are <code>about:blank</code>, which displays a blank HTML document, and simply <code>about:</code>, which may display information about the browser. Some browsers use URIs beginning with the name of the browser for similar purposes, and many <code>about</code> URIs will be translated into the appropriate URI if entered. Examples are <code>opera</code> ([[Opera (browser)|Opera]]) or <code>chrome</code> ([[Google Chrome]]). An exception is <code>about:blank</code>, which is not translated.

In early versions of [[Netscape Navigator|Netscape]], any [[Uniform Resource Identifier|URI]] beginning with <code>about:</code> 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]], <code>about:</code> followed by a string of [[HTML]] (e.g. <code><nowiki>about:&lt;em&gt;hello world&lt;/em&gt;</nowiki></code>) 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 {{IETF RFC|2397}}. Still other versions of Netscape would return various phrases in response to an unknown <code>about</code> 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 [[Sketch comedy|skit]] on the TV show ''[[In Living Color]]'').<ref>{{cite newsgroup |url=https://groups.google.com/d/msg/comp.infosystems.www.browsers.mac/CqOPxiKDdl4/t_98xJalHwMJ |author=Dominik Hoffmann |date=1996-06-14 |title=Special Netscape URLs for cache diagnostics? |newsgroup=comp.infosystems.www.browsers.mac |access-date=2012-09-29}}</ref><ref>{{cite newsgroup |url=https://groups.google.com/d/msg/comp.infosystems.www.browsers.mac/jlXT_CEjXXw/OJniq4unjiEJ |author=Matthew Paul Thomas |date=2000-06-23 |access-date=2012-09-29 |title=Weird easter egg in NN 3.0 or 3.01}}</ref>
==Standardization==
In 2010, and onwards, there are efforts to standardize the <code>about</code> URI scheme, and define the processing requirements for some specific URIs, in the IETF Applications Area Working Group (APPSAWG).<ref>{{cite web |url=http://tools.ietf.org/wg/appsawg/ |title=Appsawg Status Pages |publisher=IETF}}</ref> In August 2012, it was published as an official [[Request for Comments]] as {{IETF RFC|6694}}. The <code>about</code> URIs that have since been defined and assigned by [[Internet Assigned Numbers Authority|IANA]] are listed below.<ref>{{cite web |url=https://www.iana.org/assignments/about-uri-tokens/about-uri-tokens.xhtml |title="about" URI Tokens |website=www.iana.org |access-date=2017-06-28}}</ref>

{| class="wikitable"
|-
!URI
!Purpose
|-
| '''about:blank'''<ref name="rfc">RFC 6694</ref>
|References 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. <code>&lt;!DOCTYPE html SYSTEM "about:legacy-compat"&gt;</code>.
|-
| '''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.<ref>{{cite web|url=https://www.w3.org/TR/css-values/#about-invalid|title=CSS Values and Units Module Level 3|website=www.w3.org|language=en|access-date=2017-06-28}}</ref>
|-
| '''about:html-kind'''
|Used as an identifier for kinds of media tracks.<ref>{{cite web|url=https://html.spec.whatwg.org/multipage/urls-and-fetching.html#about:html-kind|title=HTML Standard}}</ref>
|}

==Common==
{| class="wikitable"
|+ Common "about:" URIs
! rowspan="2" |URI
! colspan="6" |Purpose
|-
! [[Firefox]], [[SeaMonkey]], [[Mozilla Application Suite|Mozilla]]
! [[Google Chrome]], [[Chromium (web browser)|Chromium]]
! [[Konqueror]]
! [[Opera (web browser)|Opera]]
! [[Microsoft Edge|Edge]]
! [[Internet Explorer]]
|-
| '''about:'''
| {{N/A|Deprecated in [[Firefox 57]] (Firefox Quantum)}}
| Redirects to "chrome://version"
| Redirects to "about:konqueror"
| Redirects to "opera:about"
| Redirects to "edge://version"
| {{N/A}}
|-
| '''about:about'''
| Lists all the about: URLs <br /> (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"
| {{N/A}}
|-
| '''about:blank'''
| colspan="6" style="text-align:center;" | Shows a blank document
|-
| '''about:plugins'''
| Shows the filename, [[MIME type]], description, suffix, and status of all installed plug-ins
| {{N/A|Deprecated in Chrome 57}}<ref name=":0">{{Cite web|url=https://bugs.chromium.org/p/chromium/issues/detail?id=615738|title=Issue 615738: Deprecate "chrome :// plugins"|website=bugs.chromium.org|access-date=2022-03-28}}</ref>
| Shows the filename, [[MIME type]], description, suffix, and status of all installed plug-ins
| Redirects to "opera:plugins"
| {{N/A}}
| {{N/A}}
|-
| '''about:cache'''
| Shows information about the Cache Service.
| {{N/A|Deprecated in Chrome 66}}<ref name=":1">{{Cite web|url=https://bugs.chromium.org/p/chromium/issues/detail?id=811956|title=Issue 811956: Remove "chrome :// view-http-cache"|website=bugs.chromium.org|access-date=2022-03-28}}</ref>
| Redirects to "about:konqueror"
| Redirects to "opera:cache"
| {{N/A}}
| {{N/A}}
|-
| '''about:mozilla'''
| Shows a page from the fictional ''[[The Book of Mozilla|Book of Mozilla]]''. In some versions of Netscape, also replaced the meteors in the standard Netscape [[throbber]] with a large fire-breathing lizard.
| {{N/A}}
| Redirects to "about:konqueror"
| {{N/A}}
| {{N/A}}
| Shows a blank HTML document with a [[blue]] background. Removed in [[Windows XP]] [[Service pack|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 (web browser)|Chromium]] project, including [[Google Chrome]], [[Microsoft Edge]], [[Opera (web browser)|Opera]], and [[Vivaldi (web browser)|Vivaldi]].
{| class="wikitable"
|+ Chrome-specific "about:" URIs
!  URI<ref name="AboutLinks">{{cite web|url=https://code.google.com/p/chromium/wiki/AboutLinks|title=AboutLinks|access-date=19 September 2014|date=22 December 2010|publisher=Google Code|work=code.google.com/|url-status=dead|archive-date=12 September 2014|archive-url=https://web.archive.org/web/20140912052512/https://code.google.com/p/chromium/wiki/AboutLinks}}</ref>
!  Purpose
|-
| '''about:cache'''
| Deprecated in version 66<ref name=":1" />
|-
| '''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 <code>about:surf</code> (see below.)<ref>{{cite web |last1=Gunnell |first1=Marshall |title=36 Hidden Google Search Games and Easter Eggs |url=https://www.howtogeek.com/690469/36-hidden-google-search-games-and-easter-eggs/ |website=How-To Geek |publisher=LifeSavvy Media |date=26 September 2020}}</ref>
|-
| '''about:dns'''
| Displays the DNS records
|-
| '''about:flags'''
| Displays a page where experimental features can be configured by setting [[Feature toggle|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 "[[Series of tubes|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)<ref name=":0" />
|-
| '''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.<ref name="About protocol links">{{cite web|url=http://kb.mozillazine.org/About_protocol_links|title=About protocol links|access-date=19 September 2014|publisher=mozillaZine}}</ref>
{| class="wikitable"
|+ Mozilla-specific "about:" URIs
! rowspan="2" |URIs
! colspan="2" |Purpose
|-
! [[Firefox]]
! [[SeaMonkey]], [[Mozilla Application Suite]]
|-
| '''about:addons'''
| colspan="2" | 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
| {{N/A}}
|-
| '''about:bloat'''
| Displays BloatView output (disabled in release builds). Superseded by '''about:memory''' on Gecko 1.9.2.<ref name="mozdev leaks">{{cite web |url=https://developer.mozilla.org/en/Debugging_memory_leaks |title=Debugging memory leaks |publisher=Mozilla Developer Network |access-date=2010-08-10 |archive-date=2010-12-23 |archive-url=https://web.archive.org/web/20101223004238/https://developer.mozilla.org/en/Debugging_memory_leaks |url-status=dead }}</ref>
| {{N/A}}
|-
|'''about:bloat?new'''
| TBA
| {{N/A}}
|-
|'''about:bloat?clear'''
| TBA
| {{N/A}}
|-
| '''about:blocked'''
| Shows the [[malware]] protection page used when the browser identifies a page as not safe for viewing (Firefox 3+)
| {{N/A}}
|-
| '''about:buildconfig'''
| colspan="2" | Shows the arguments and options used to compile the build in use
|-
| '''about:cache'''
| colspan="2" | 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'''
| colspan="2" | Shows individual entries in memory
|-
| '''about:cache?device=disk'''
| colspan="2" | Shows individual entries on disk
|-
| '''about:cache?device=offline'''
| colspan="2" | Shows individual entries for offline viewing (Gecko 1.9+)
|-
| '''about:cache-entry'''
| colspan="2" | Shows information about a cache entry. Used in about:cache links. Requires parameters.
|-
| '''about:certerror'''
| colspan="2" | Shows the error page used when an [[Transport Layer Security|SSL/TLS]] certificate is untrusted or otherwise invalid
|-
| '''about:config'''
| colspan="2" | Shows an interface for viewing and setting a wide variety of configuration variables, many of which are not otherwise accessible through the [[graphical user interface|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.<ref>{{cite web |url= https://bugzilla.mozilla.org/show_bug.cgi?id=446704 |title=446704 - "This might void your warranty!" is not appreciated by corporate customers. |date=2008-07-22 |access-date=2014-07-07 |website=Bugzilla |publisher=Mozilla}}</ref> The message has a checkbox to turn it off.
|-
| '''about:crashes'''
| colspan="2" | Shows details of crashes submitted by Mozilla's crash reporter (Firefox 3+, SeaMonkey 2.0+)
|-
| '''about:credits'''
| colspan="2" | Shows a list of all those who contributed to Mozilla
|-
| '''about:devtools'''
| colspan="2" | Shows the welcome page used by Firefox Developer Tools
|-
| '''about:downloads'''
| colspan="2" | Shows a list of downloaded files
|-
| '''about:feeds'''
| colspan="2" | Shows the page used when clicking the rss feed icon in the address bar
|-
| '''about:healthreport'''
| colspan="2" | Shows the Firefox Health Report
|-
| '''about:home'''
| Shows the Firefox 4 default home page
| {{N/A}}
|-
|'''about:jetpack'''
| Shows an interface for viewing and setting the [[Jetpack (Firefox project)|JetPack extension]]
| {{N/A}}
|-
| '''about:licence'''
| colspan="2" | 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'''
| colspan="2" | Shows the [[Mozilla Public License]] (and the [[Netscape Public License]]) for the piece of software (Gecko 1.8+)
|-
| '''about:logo'''
| colspan="2" | Shows the logo used on the '''about:''' screen
|-
| '''about:memory'''
| colspan="2" | Shows memory usage (Firefox 3.6+)
|-
| '''about:mozilla'''
| colspan="2" | Easter egg, shows a verse from [[The Book of Mozilla]]
|-
| '''about:neterror'''
| colspan="2" | 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 [[Sideloading|sideload]] an add-on, a dialog box bearing this URI appears. asking for the user's explicit consent.
|{{N/A}}
|-
| '''about:newtab'''
| colspan="2" | Shows a grid of favourite and most-visited websites (Firefox 13+)
|-
| '''about:permissions'''
|Shows permissions for all sites on Firefox 6.0a1
| {{N/A}}
|-
| '''about:plugins'''
| colspan="2" | Shows installed, currently enabled plug-ins
|-
| '''about:preferences'''
| colspan="2" | 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
| {{N/A}}
|-
|'''about:reader?url='''
| Opens the specified URL in Reader Mode. For example, <code>about:reader?url=<nowiki>http://example.com</nowiki></code>.
| {{N/A}}
|-
| '''about:rights'''
| colspan="2" | Shows licensing information
|-
| '''about:robots'''
| Easter egg, beginning with March 8, 2008 trunk builds. The title of a window cites [[Klaatu barada nikto|the iconic phrase]] of ''[[The Day the Earth Stood Still]]''.<ref>{{cite web |url=https://bugzilla.mozilla.org/show_bug.cgi?id=417302 |title=Bug 417302 — about:robots |publisher=Mozilla Project Bugzilla}}</ref> The page's prose cites [[Isaac Asimov's Three Laws of Robotics|Isaac Asimov's first law of robotics]].
| {{N/A}}
|-
| '''about:sessionrestore'''
| colspan="2" | Shows an interface for viewing about last session.
|-
| '''about:startpage'''
| colspan="2" | In Ubuntu, shows the Ubuntu start page with the current search engine (if the "Ubuntu Firefox Modifications – ubufox" add-on is installed)
|-
| '''about:support'''
| colspan="2" | Shows troubleshooting information (Firefox 3.6+, SeaMonkey 2.1+)
|-
| '''about:sync-tabs'''
| colspan="2" | Shows list of tabs from other computers. Requires enabled synchronization.
|-
|'''about:tabcrashed'''
| Contains the text displayed when a [[Tabbed browser|tab]] crashes. Added in Firefox 25.
| {{N/A}}
|-
| '''about:webrtc'''
| colspan="2" | Shows an interface for [[WebRTC]] internals
|-
| '''about:welcome'''
| colspan="2" | Shows the welcome page used by Firefox
|}

==Opera (v1–15)==
In [[Opera (web browser)|Opera]], <code>about:</code> is an alias for the <code>opera:</code> scheme; therefore all these URIs also work with about prefixed. User [[JavaScript]] is disabled for all URIs in the <code>about:</code> or <code>opera:</code> schemes as a security feature. These pages can, however, be styled using local [[Cascading Style Sheets|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 <code>opera:about</code>.

{| class="wikitable"
|+ Opera-specific "about:" URIs
!  URIs
!  Purpose
|-
| '''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'''
| Shows a page that allows changing of numerous browser preferences, many of which cannot be accessed through the normal Preferences window (Opera 9.0 and newer)
|-
| '''opera:drives'''
| Shows the local drives of the host system
|-
| '''opera:history'''
| Shows the content of the browser history
|-
| '''opera:historysearch'''
| Shows the start page of internal search engine for the browser history (Opera 9.5 and newer)
|-
| '''opera:plugins'''
| Shows installed plug-ins. Opera 11 and newer allow individual plug-ins to be disabled from this page.
|-
| '''opera:button'''
| Defines a custom button as a set of Opera actions. (Note: This does not work directly, all button parameters as on CustomButtons need be specified.)
|-
| '''opera:help'''
| Shortcut to the help directory. This can be either local or external.
|-
| '''opera:debug'''
| Shows a page that allows changing of settings for remote debug of Opera via [[Opera Dragonfly]] (Opera 9.5 and newer)
|-
| '''opera:memdebug'''
| Shows debug information about memory usage (Opera 9.5 and newer)
|-
| '''opera:webstorage'''
| Shows the browser's [[Web storage|Web Storage]] (Opera 10.5 and newer)
|-
| '''opera:webdatabases'''
| Shows the browser's Web Storage databases (Opera 10.5 and newer)
|-
| '''opera:gpu'''
| Shows information about hardware accelerated graphics and GPU support
|-
| '''opera:cpu'''
| Displays CPU usage (Opera 12 beta and newer)
|}

==Internet Explorer (6–11)==
Internet Explorer about URIs are configurable in [[Microsoft Windows|Windows]]. It is therefore possible that some of the listed URIs will not work on a particular computer. For example, "[[The Book of Mozilla|about:mozilla]]" was removed in SP2 (although the page can still be found at "res://mshtml.dll/about.moz"). <!-- To configure about URIs, open the Registry Editor and browse to: "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\AboutURLs". --> These about URIs are sometimes used for spyware and adware, most notably in [[CoolWebSearch]], which made about:blank display advertisements.

Any <code>about</code> URI that is not recognized by Internet Explorer redirects to a page saying "Navigation to the webpage was canceled."

{| class="wikitable"
|+ Internet Explorer-specific "about:" URIs
!  URI
!Purpose
!Supported versions
|-
| '''about:home'''
|Displays the user's home page.
|6, 7, 9, 10, 11 (not 8)
|-
| '''about:desktopitemnavigationfailure'''
| rowspan="3" |Displays the "navigation cancelled" page.
| rowspan="3" |6–8
|-
| '''about:navigationcanceled'''
|-
| '''about:navigationfailure'''
|-
| '''about:noadd-ons'''
|Appears when add-ons are disabled to notify the users of a change in their web browsing experience.
|7–11
|-
| '''about:noadd-onsinfo'''
|Contains information about add-ons and what they do.
|7–11
|-
| '''about:offlineinformation'''
|Informs the user that the current page cannot be viewed offline. [[Internet Explorer 9]] and later do not support offline browsing.
|6–8
|-
| '''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.
|6–11
|-
| '''about:securityrisk'''
|Informs the user not to browse with the current security settings because they may be harmful to the computer.
|6–11
|-
| '''about:tabs'''
|Informs the user about [[tabbed browsing]]. Internet Explorer shows this page upon creating a new tab if the "Open home page for new tabs instead of a blank page" setting is enabled.
|7–11
|-
| '''about:inprivate'''
|Appears when the use initiates [[InPrivate Browsing]]; contains information about this feature.
|9–11
|-
| '''about:compat'''
|Displays a table of sites and the document rendering emulation mode configured for maximum  backward compatibility.<ref>{{cite web |url= https://docs.microsoft.com/en-us/internet-explorer/ie11-deploy-guide/what-is-enterprise-mode#enterprise-mode-and-the-enterprise-mode-site-list-xml-file |title=Enterprise Mode and the Enterprise Mode Site List (Internet Explorer 11 for IT Pros) |publisher=Docs.microsoft.com |access-date=2018-06-19}}</ref>
|11
|-
| '''about:newsfeed'''
|Displays Internet Explorer 11's signature start page. It contains a [[Microsoft Bing]] search bar at the top, followed by a customizable row of tiles pertaining [[Bookmark (digital)|bookmarked]] website, a row of news topic category selection links, and an infinitely scrolling news aggregation feed.
|11
|}

==Microsoft Edge Legacy (v20–44)==
The following applies to [[Microsoft Edge Legacy]] version 20 through 44. For newer Edge versions, see [[About URI scheme#Chrome and Chromium derivatives|the Chromium section]].
{| class="wikitable"
|+ [[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.
|}

==GNOME Web==
When [[GNOME Web]] (formerly Epiphany) used [[Gecko (software)|Gecko]] as its layout engine, all Firefox-specific <code>about:</code> URIs worked in it. After the adoption of [[WebKit]] as its layout engine, only the following URIs are supported.{{citation needed|date=November 2011}}

{| class="wikitable"
|+ GNOME Web-specific "about:" URIs
! URI
! Purpose
|-
| '''about:plugins'''
| Shows installed plug-ins.
|-
| '''about:memory'''
| Shows details about memory usage.
|-
| '''about:epiphany'''
| Displays the following message:<ref>{{cite web |url=//blogs.gnome.org/xan/files/2012/03/about-epiphany.png |title=Screenshot of Epiphany 3.4}}</ref>
{{quotation|{{Verse translation|lang=fr|''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 [[Epiphany (web browser)#Web Application Mode|Web Application Mode]], supported since release 3.2.<ref>{{cite web
|url        = https://git.gnome.org/browse/epiphany/plain/NEWS
|title      = ''NEWS'' file
|publisher  = The GNOME Project's [[Git (software)|git repository]]
|access-date = 2011-10-17
}}</ref>
|-
| '''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.
|}

==Netscape==
The about: URL originated in and has existed in all versions of [[Netscape]] browsers.  It was originally added as an [[Easter egg (media)|Easter egg]] to display information about the development team.<ref>{{cite web |url=http://www.montulli.org/lou/about_urls |title=A short history of the about: URL}}</ref>

Older versions of the [[Netscape]] browser have an <code>about:people</code> URI that was similar to <code>about:credits</code> above, but it would redirect to Netscape's active employee listing. In addition, <code>about:''username''</code>, where ''username'' is the username of a Netscape employee, would redirect to the Netscape homepage of the employee specified. For example, <code>about:jwz</code> would redirect to '''<nowiki>http://people.netscape.com/jwz/</nowiki>''' (not an active link).<ref>{{cite web |url=http://www.yikes.com/netscape/people.html |title=About: Netscape People |publisher=Yikes! |access-date=2006-04-21 |archive-url=https://web.archive.org/web/20060520022154/http://www.yikes.com/netscape/people.html |archive-date=2006-05-20 |url-status=dead }}</ref> 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|date=March 2010}}

Many other <code>about:</code> 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.<ref name="benoit">{{cite web |url=http://www.rigaut.com/benoit/CERN/about/ |title=This page is dedicated to Netscape Navigator 3.0b4 and followers, oops Mozilla 3.0b4 and friends! |access-date=2010-11-16 |archive-date=2020-10-24 |archive-url=https://web.archive.org/web/20201024233431/http://www.rigaut.com/benoit/CERN/about/ |url-status=dead }}</ref>

Some versions of Netscape would display the browser history for the <code>about:global</code> URI.<ref name="benoit"/>

==Others==
* In [[Konqueror]], any <code>about</code> URI except <code>about:blank</code> and <code>about:plugins</code> redirects to <code>about:konqueror</code>, which shows a friendly ‘start’ and navigation page.
* In [[Internet Explorer for Mac]] 5 was an offline [[Easter egg (media)|Easter egg]], accessible by typing ‘about:[[tasman (browser engine)|tasman]]’, showing the [[Acid1]] test with the text replaced by the names of the developers.<ref>{{cite web|url=http://www.eeggs.com/items/14448.html |title=Internet Explorer Easter Egg — IE5 Mac Team |publisher=The Easter Egg Archive |date=2000-06-19}}</ref>
* [[Safari (web browser)|Safari]] only recognizes <code>about:blank</code>.
* [[Microsoft Outlook]] supports an additional <code>outlook:today</code> URI, which shows the Outlook Today Screen. This screen shows messages, tasks and appointments; it is also accessible from Internet Explorer. Outlook recognizes <code>about:blank</code> too, but no other "about:" URIs.

==References==
{{Reflist}}

==External links==
*{{IETF RFC|6694}} - The "about" URI Scheme
*[http://kb.mozillazine.org/About_protocol_links About protocol links] in Mozilla and Mozilla Firefox.
*[https://lxr.mozilla.org/seamonkey/source/docshell/build/nsDocShellModule.cpp#138 about redirectors' source code]{{Dead link|date=June 2020 |bot=InternetArchiveBot |fix-attempted=yes }} in Firefox

{{URI scheme}}

[[Category:Web browsers]]
[[Category:Mozilla]]
[[Category:URI schemes]]