about 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.
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
| 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]
| 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.
| 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 the customizable (default) start page. |
| about:tabs | Shows the (default) new tab page. |
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
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:
| URI | Epiphany |
|---|---|
| about:blank | Displays the blank page. |
| about:plugins | Shows installed plug-ins. |
| about:epiphany | Displays the following message:[11]
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] |
| 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:peopleURI that was similar toabout:creditsabove, 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:jwzwould 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.
- 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:globalURI[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
Only about:blank is accepted, all other about: URIs trigger default address bar behavior (e.g. a Google search).
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
- ↑ The term “about:blank” is also the generic name for a group of variants of the CoolWebSearch malware program group.
- ↑ It seems that perfection is attained not when there remains nothing to add, but when there remains nothing to remove.
References
- ↑ Dominik Hoffmann (1996-06-14). "Special Netscape URLs for cache diagnostics?". Newsgroup: comp.infosystems.www.browsers.mac. Retrieved 2012-09-29.
- ↑ Matthew Paul Thomas (2000-06-23). "Weird easter egg in NN 3.0 or 3.01". Retrieved 2012-09-29.
- ↑ "Appsawg Status Pages". IETF.
- ↑ "Web Specifications supported in Opera 6". Opera.
- ↑ RFC 6694
- ↑ "About protocol links". mizillaZine. Retrieved 19 September 2014.
- ↑ "Debugging memory leaks". Mozilla Developer Network.
- ↑ "446704 - "This might void your warranty!" is not appreciated by corporate customers.". Bugzilla @ Mozilla. 2008-07-22. Retrieved 2014-07-07.
- ↑ "Bug 417302 — about:robots". Mozilla Project Bugzilla.
- ↑ "AboutLinks". code.google.com/. Google Code. 22 December 2010. Retrieved 19 September 2014.
- ↑ "Screenshot of Epiphany 3.4".
- ↑ "NEWS file". The GNOME Project's git repository. Retrieved 2011-10-17.
- ↑ "A short history of the about: URL".
- ↑ "About: Netscape People". Yikes!.
- 1 2 "This page is dedicated to Netscape Navigator 3.0b4 and followers, oops Mozilla 3.0b4 and friends!".
- ↑ "Internet Explorer Easter Egg — IE5 Mac Team". The Easter Egg Archive. 2000-06-19.
External links
- RFC 6694 - The "about" URI Scheme
- About protocol links in Mozilla and Mozilla Firefox.
- about redirectors' source code in Firefox
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