Overview of Preferences

Most of Mozilla's behavior is customizable either through CSS or through preferences.

Browse the Edit->Preferences dialog now and then after you update to a new Mozilla version; some interesting new prefs show up from time to time.

But only a small fraction of preferences are exposed in the Preferences dialog.  There's a lot more you can customize, if you want to.

• about:config.  Double-click on a pref line to edit it: this will change it in your running Mozilla, but may not save it.
  
• user.js: Preferences saved here will not be overwritten by Mozilla, and will override anything in prefs.js.  user.js lives in your profile directory; you will have to create this file the first time you use it; you don't have one by default.