About:
- The title of this article is incorrect because of technical limitations. The correct title is about:.
- For other uses, see About:Blank (disambiguation).
about: is used as an internal "protocol" or "URL (or URI) scheme" in various web browsers to display certain built-in functions and Easter eggs. It is not an officially-registered scheme.
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. And in early versions of Internet Explorer, about: followed by a string of HTML (e.g. about:<b>hello world</b>) would render that string as though it was the source of the page - thus providing a similar (though more limited) facility to the data: URL defined by RFC 2397.
The most commonly implemented about: URLs are about:blank, which displays a blank HTML document, and simply about:, which displays information about the browser. Opera uses URLs beginning opera: for similar purposes, and many about: URLs will be translated into an appropriate opera: URL if entered; an exception is about:blank, which is not translated to opera:blank.
| Contents |
Common about: addresses
| Addresses | Mozilla | Mozilla Firefox | Opera | Internet Explorer |
|---|---|---|---|---|
| about: | Shows version information and copyright information | Translated to "opera:about" | ||
| about:about | Lists all the about: addresses | Translated to "opera:about" | ||
| about:blank | 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" | ||
| about:cache | Shows information about the Cache Service. | Translated to "opera:cache" | ||
| about:mozilla | Shows a page from the fictional Book of Mozilla. | This showed a blank HTML document with blue background color. Possibly a joke reference to the "blue screen of death". Removed in Windows XP SP2. | ||
Mozilla-specific about: addresses
| Addresses | Mozilla | 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 | |
Internet Explorer-specific about: addresses
Note: Internet Explorer about: addresses are configurable. 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 Cool Web Search, which made about:blank turn into a page with overpriced products.
| 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. |
Other about: URLs
- Older versions of the Netscape browser used to have an about:people link that was similar to about:credits above, and about:jwz will even redirect to the homepage of one of the application's authors, Jamie Zawinski [1].
External links
- About protocol links in Mozilla and Mozilla Firefox.