In addition to the changes that can be made in the Options window, Firefox can further be customized by editing certain configuration files. This page describes how to access and change these file.

Table Of Contents

• about:config
• Configuration Files
• Locate your profile folder
• userChrome.css
• userContent.css
• user.js

about:config

Many of the tips and tricks mentioned on this site require you to use about:config. To access about:config, type about:config in the Location bar, and press EnterReturn. This will display a list of used preferences, as well as a search bar at the top.

Double-click on a preference to change its value. To do add a new preference, open the context menu (right-click) on any existing preference, go to the New menu, and select the type of preference.

Configuration Files

Some tips and tricks require that you edit configuration files manually. There are three files you should know about:

userChrome.css

Used to change the appearance of the browser.

userContent.css

Used to change the appearance of web pages.

user.js

Used to change various preferences.

All these files are plain text files you need to create in your profile folder and can be edited using a standard text editor, such as Notepad on Windows, TextEdit on Mac, and gedit or kate on Linux.

Locate your profile folder

Before the configuration files are presented, you should know how to find your profile folder, which is where Firefox saves all your settings on your hard drive. To locate your profile folder, see How to find your profile.

userChrome.css

This file sets the display rules for various elements in the Firefox user interface and is located in the sub-folder called chrome in your profile folder. This file does not exist by default, so you need to create it before you can start adding your preferences. There's an example file that exists by default, called userChrome-example.css. You can just rename that file by removing the -example part.

userContent.css

This file sets the display rules for web content and is located in the sub-folder called chrome in your profile folder. As with userChrome.css, this file does not exist by default, so you need to create it before you can start adding your preferences. As with userChrome.css, there is an example file that exists by default, called userContent-example.css. Basically, you can just rename that file by removing the -example part.

user.js

This is the main preferences file for Firefox and is located in your profile folder. The file does not exist by default, so you need to create it before you can start adding your preferences. In almost all cases, edits made using the user.js can be done via about:config, which is the recommended method.