About:config

What is about:config

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

Warning: Changing these values can, in rare circumstances, break Mozilla, 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, you can type "about:config" in the Location Bar. In Thunderbird, you could set your Mail Start page in the Options to "chrome://global/content/config.xul" (you can press a button when Bug 262626 is fixed).

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: strings.