about: URI scheme

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about: is an internal URI scheme (also known as a "URL scheme" or, erroneously, "protocol") in various web browsers to display certain built-in functions. It is not an officially registered scheme, and has no standard syntax.

In early versions of Netscape, any address beginning about: which wasn't recognised 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 was 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: address, 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).

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 not work:


[edit] Common about: addresses

Common about: addresses
Addresses Mozilla/SeaMonkey Mozilla Firefox Opera Internet Explorer Konqueror Safari Google Chrome MSN Explorer
about: Shows version information and copyright information Translated to "opera:about" Translated to "about:konqueror" Shows version information and copyright information Shows a blank page
about:about Lists all the about: addresses Translated to "opera:about" Translated to "about:konqueror" Shows nothing but the text:"about"
about:blank[1] Shows a blank HTML document
about:plugins Shows the filename, MIME type, description, suffix, and status of all installed plug-ins Translated to "opera:plugins" Shows the filename, MIME type, description, suffix, and status of all installed plug-ins Shows the filename, MIME type, description, suffix, and status of all installed plug-ins
about:cache Shows information about the Cache Service. Translated to "opera:cache" Translated to "about:konqueror" Lists the URIs of pages stored within the cache, with each linking to view-cache:uri that provides more information about the page
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. 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. Translated to "about:konqueror"

[edit] Mozilla-specific about: addresses

Mozilla-specific about: addresses
Addresses Mozilla Application Suite / SeaMonkey Mozilla Firefox
about:bloat Displays BloatView output (disabled in release builds).
about:blocked Shows the malware protection page used when the browser identifies a page as not safe for viewing. (Firefox 3-specific).
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. New to products based on Gecko 1.9 or later.
about:cache-entry Shows information about a cache entry. Used in about:cache links. Requires parameters.
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)
about:crashes Shows details of crashes submitted by Mozilla's crash reporter (since Firefox 3).
about:credits Shows a list of all those who contributed to Mozilla
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)
about:license Shows the Mozilla Public License (and the Netscape Public License) for the piece of software. (Only in products based on Gecko 1.8 or later)
about:logo Shows the logo used on the about: screen
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:plugins Shows installed plug-ins.
about:robots Easter egg, beginning with March 8th, 2008 trunk builds.[2]
about:rights Shows licensing information.

[edit] Flock-specific about: addresses

Beginning in Flock 0.9, Flock introduced a feature called My World, a place where the user's favorites, RSS feeds and favorite media can be found.

Address Flock
about:myworld Shows the My World page.
about:tutorial Shows the Flock tutorial page.

[edit] Opera-specific about: addresses

about: is an alias for opera:, therefore all these addresses also work with about: prefixed. User JavaScript is disabled for all addresses 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 about:blank combination, work in the Nintendo DS version of the Opera browser, the Nintendo DS Browser.

Opera-specific about: addresses
Addresses 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 Shows the local drives of the host system.
opera:history Shows the content of the browser history.
opera:plugins Shows installed plug-ins.
opera:button Defines a custom button as a set of Opera actions. (Note: This does not appear to work in Opera 9.5 --and possibly from an even earlier version-- upward.)
opera:help Shortcut to the help directory. This can be either local or external.

[edit] Internet Explorer-specific about: addresses

Note: Internet Explorer about: addresses are configurable in Windows. It is therefore possible that some of the listed addresses don't work. For example "about:mozilla" was removed in SP2 (although the page can still be found at "res://mshtml.dll/about.moz"). These about: addresses are sometimes used for spyware and adware, most notably in CoolWebSearch, which made about:blank display advertisements.

Address Internet Explorer 6(SP2) Internet Explorer 7 Internet Explorer 8
about:DesktopItemNavigationFailure Displays "navigation cancelled" page.
about:Home Displays the user's home page.
about:NavigationCanceled Displays "navigation cancelled" page.
about:NavigationFailure Displays "navigation cancelled" page.
about:NoAdd-ons Displays information page when add-ons are disabled.
about:OfflineInformation Informs the user that the current page can not be viewed off line.
about:PostNotCached Informs the user that to refresh the current page, information entered in a form will have to be re-posted.
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.

[edit] Google Chrome-specific about: addresses

Address Google Chrome
about:cache Shows the content of the cache.
about:crash Displays "Aw, snap!" crash notification page.
about:credits Displayes the list of free and open source software used in the browser, and their associated copyright licences.
about:dns Displays the DNS records
about:histograms Displays histograms
about:internets 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.
about:memory Displays the process manager
about:network Provides an interface for monitoring the network usage and performance statistics
about:plugins Shows installed plug-ins.
about:stats Displays statistics about processes. At the top of the page, it states "Shhh! This page is secret!"
about:shorthang Hangs the tab's process, making it become unresponsive. This is designed for testing the hanging protection
about:version Displays version information, same as about:

[edit] Konqueror

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

Address Konqueror
about:konqueror Shows a friendly 'start' and navigation page

[edit] Epiphany

Since Epiphany uses Gecko as its layout engine, the general and Mozilla-specific about: addresses work as in Mozilla (or Mozilla Firefox, depending on which branch of Gecko is used).

Additionally, about:epiphany yields a quote attributed to Antoine de Saint-Exupéry:

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.

Antoine de Saint-Exupéry

Translated as: It seems that perfection is attained not when there remains nothing to add, but when there remains nothing to remove, this can be seen as a rejoinder to critics who claim that the browser's (and the GNOME desktop's) focus on usability has led to a lack of features.

[edit] Netscape (historic)

  • Older versions of the Netscape browser have an about:people URL 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) [3] [4].
  • Not all employee pages were accessible through this scheme. Only developers that 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:deutsche showing Mozilla in Lederhosen.
  • Some versions of Netscape would display the browser history for the about:global address

[edit] Safari

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

[edit] Microsoft Outlook

In Microsoft Outlook, an additional outlook:today URI was added, which showed the Outlook Today Screen (it shows messages, tasks and appointments). 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.

[edit] External links

[edit] Notes and References

  1. ^  The term "about:blank" is also the generic name for a group of variants of the CoolWebSearch malware program group.
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