From MozillaZine Knowledge Base
There are a few special URLs, which begin with about:, that you can type into the Location Bar. (In Thunderbird, which has no Location Bar, or in SeaMonkey, you can also use them as "Mail Start Page".)
- about: — The same page as "Help -> About" (except that, on some applications, Help → About is a much smaller popup).
- about:about — Lists all these about: URLs (Mozilla Suite/SeaMonkey or Firefox 4 and newer only).
- about:addons — The "new" addons manager, in trunk builds dated 2010-05-11 or later.
- about:blank — A blank page. Useful for setting as your homepage.
- about:bloat — Displays BloatView output (disabled in release builds).
- about:buildconfig — Reveals details about your Mozilla build options.
- about:cache — Displays cache statistics and disk cache directory location.
- about:cache?device=memory — Lists memory cache entries.
- about:cache?device=disk — Lists disk cache entries.
- about:cache-entry — Shows information about a cache entry. Used in about:cache links. Requires parameters.
- about:config — GUI for modifying user preferences. (Also accessible in Thunderbird by means of the "Config Editor" button in the "Advanced" Preferences).
- about:crashes — List of Breakpad crash reports, with links and datestamps. Only in products based on Gecko 1.9 or later (Firefox 3, Thunderbird 3, SeaMonkey 2).
- about:credits — The list of contributors to the Mozilla projects.
- about:data — opens the Data Manager which shows per-site data and permissions. This is part of SeaMonkey 2.x and available as a Firefox extension.
- about:downloads — new on Firefox 20. (Also in recent versions of SeaMonkey. Jökulsárlón Download Manager may be required.)
- about:home — Firefox Start Page
- about:healthreport — new on Firefox 21 (bug 718066, bug 719484). Also accessible via "Help -> Firefox Health Report".
- about:kitchensink — Was never included in Mozilla for the reasons listed in bug 122411 ("Mozilla does not have a kitchen sink"). You can install an extension that adds it though :)
- about:licence and about:license — both show 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 — Displays the application logo (Mozilla Suite, SeaMonkey, and Firefox 3).
- about:memory shows the memory usage of Firefox starting in Firefox 3.6 (Windows) and Firefox 4 (Linux). Implemented in bug 515354
- about:mozilla — The famous Book of Mozilla
- about:newtab — the default new tab page since Firefox 13.
- about:permissions shows and manages the permissions as also shown in Tools → Page Info → Permissions. Implemented starting with Firefox 6 (bug 573176)
- about:plugins — Lists all your plugins as well as other useful information.
- about:robots — Easter egg, see bug 417302. Beginning with March 8th, 2008 trunk builds, it's now available on Firefox 3.0b5.
- about:support — Starting in Firefox 3.6 (bug 367596) and SeaMonkey 2.1a trunk builds based on Gecko 1.9.3a (bug 518607). Displays information such as Application Basics (version, link to open the profile folder, link to about:plugins and about:buildconfig), Extensions, Modified Preferences and, starting in Firefox 4, Graphics information (bug 587102). Also accessible via "Help -> Troubleshooting information".
- about:telemetry — new on Firefox/Thunderbird 19 and SeaMonkey 2.16 (bug 661881)
Certain extensions add a few additional about: URLs.