About:config

about:config is a special location that lists all application preferences (read from "prefs.js" and "user.js"), many of which are not present in Options/Preferences dialog. Preferences can also be changed here.

Warning: Changing these values can, in rare circumstances, break Mozilla Suite, Firefox, or Thunderbird or cause strange behavior. Only edit these preferences if you know what you are doing.

Opening about:config

In Firefox and Mozilla Suite, you can type "about:config" in the Location Bar.

In Thunderbird, use AboutConfig extension. (See also Bug 262626.)

There's a version of AboutConfig extension compatible with Nvu here.

References

• A brief guide to Mozilla preferences
• MozillaZine Tutorial for about:config — Step by step guide with screenshots.
• Preferential extension — An about:config-like extension that has some extra features (documentation for some of the preferences, for example).
• List of preferences and what they do.
• About:config entries — MozillaZine KB's list of preferences and what they do.
• About protocol links — other about: pages.