About: URI scheme

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about: is used as an internal URI scheme (also known as a "URL scheme" or, erroneously, "protocol") in various web browsers to display certain built-in functions and Easter eggs. 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 to opera:blank.

Contents 1 Common about: addresses 2 Mozilla-specific about: addresses 3 Opera-specific about: addresses 4 Internet Explorer-specific about: addresses 5 Konqueror 6 Epiphany 7 Netscape (historic) 8 External links 9 Notes and References

[edit] Common about: addresses

Common about: addresses

Addresses	Mozilla	Mozilla Firefox	Opera	Internet Explorer	Konqueror
about:	Shows version information and copyright information		Translated to "opera:about"		Translated to "about:konqueror"
about:about	Lists all the about: addresses		Translated to "opera: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
about:cache	Shows information about the Cache Service.		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.			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.

[edit] Mozilla-specific about: addresses

Mozilla-specific about: addresses

Addresses	Mozilla Suite	Mozilla Firefox
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: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:credits	Shows a list of all those who contributed to Mozilla
about:logo	Shows the logo used on the about: screen	about:logo is not available in Firefox
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)
about:mozilla	Shows a verse from the Book of Mozilla
about:neterror?e=error&u=url&d=desc	Shows the error page used when the browser could not access the requested path.

[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.

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.
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"). To configure about: addresses, open the Registry Editor and browse to: "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\AboutURLs". These about: addresses are sometimes used for spyware and adware, most notably in CoolWebSearch, which made about:blank display advertisements.

Address	Internet Explorer (SP2)
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: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.

In Internet Explorer 7, "about:Tabs" has also been included, and provides information about tabbed browsing. It is loaded by default when a new tab is created.

[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:

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) [2] [3]
• Some versions of Netscape would display the browser history for the about:global address

[edit] External links

• About protocol links in Mozilla and Mozilla Firefox.

[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.