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 RFC2397. 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]
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).[4] In August 2012, it was published as an official Request for Comments as RFC6694. The about URIs that have since been defined and assigned by IANA are listed below.[5]
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. <!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]
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 XPSP2. (The blue page can still be seen at "res://mshtml.dll/about.moz" instead.)
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.)[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.
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.[13]
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.
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
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.
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.
None of these functions, except the opera:about combination, work in the Nintendo DS Browser, which is an Opera derivative.
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 (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 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."
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
Displays the "navigation cancelled" page.
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.[17]
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 bookmarked website, a row of news topic category selection links, and an infinitely scrolling news aggregation feed.
11
Microsoft Edge (v20–44)
The following applies to Microsoft Edge version 20 through 44, which Microsoft dubs "the legacy Edge." For newer versions, see the Chromium section.
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 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]
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 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]
Others
In Konqueror, any about URI except about:blank and about:plugins redirects to about:konqueror, which shows a friendly ‘start’ and navigation page.
Microsoft Outlook supports an additional 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.
