Editing configuration

Mozilla applications are highly customizable, and there are a number of standard ways to change their appearance and behaviour. Basic settings can be changed using the application's dialog boxes. The main Options or Preferences dialogs can be reached from the "Tools" or "Edit" menus. (See menu differences in Windows, Linux, and Mac.) This article describes methods for more advanced configuration.

Modifying preferences—adding, removing and setting

To make more advanced changes to the application’s behaviour—in particular, if you have been instructed to “set a preference”—you should either edit the user.js file, or use the about:config interface. Note that whilst it is often quicker to use about:config, editing the "user.js" file has the advantage of portability: your preferences will never be overridden, and they can be transferred to a different profile, or backed up for safe keeping.

Modifying appearance

To modify the way in which Web pages and e-mails are displayed, you should edit the userContent.css file. To modify the appearance of the application itself, you should edit the userChrome.css file.

How to edit configuration files

The ChromEdit extension provides a convenient way of editing configuration files. If instead you choose to edit your configuration files using your own text editor, you should consult the Manual editing advice.

Troubleshooting

If you experience problems when editing configuration files, consult the Troubleshooting article.

External links

• The Stylish extension provides an alternative way to change styles. It does not use userContent.css or userChrome.css, and changes take effect without restarting the application.
• Extensions and themes provide many additional features and allow you to change the way your application looks.
• Editing Configuration Files at Firefox Help
• Editing Configuration Files at Thunderbird Help