Creating and Editing user.js

Creating and Editing user.js

By default, Firefox does not have a user.js file. This file must be created by the user. There is neither a way to create the user.js file from Firefox, nor does Firefox update a user.js file. The user.js file is really the final say for preferences; it is processed last and its contents override prefs.js. (Firefox does update prefs.js based on the contents of user.js.) Because Firefox automatically updates and modifies prefs.js, Mozilla recommends (and I concur) that you not modify prefs.js. Instead it suggests adding those preferences you wish to set or modify in user.js.

There are two ways to create your user.js file. The first way, and perhaps the easiest, is to simply use a basic text-based editor (such as Window's notepad program).

The second way is to copy the file prefs.js to your user.js. (Just don't rename it, you must copy!) Change whatever items in your new user.js file as necessary, and delete any extraneous lines to clean up the file. When modifying user.js, use care to observe the syntax of the file, and add any comments necessary so that should you later go back to the file, you will be able to remember why you made a certain change.

The user.js file is covered in Chapter 4, "Managing Profiles."

An excellent reference for preferences that are set in prefs.js and user.js may be found at http://preferential.mozdev.org/preferences.html. This web page documents virtually every settable preference for Firefox. (However, additional extensions and plug-ins might have settings that will not be documented at this location.)