Firefox advanced customization and configuration options

Firefox Firefox Last updated: 4 weeks ago

Firefox supports a wide range of customization options that are well-suited to all skill levels. The toolbar layout can be customized, numerous settings can be configured, and the Mozilla Add-ons directory contains a massive library of extensions and themes to add additional functionality and make Firefox reflect your own needs and personality.

Two other forms of advanced configuration allow even further customization: about:config preference modifications and userChrome.css or userContent.css custom style rules. However, Mozilla highly recommends that only the developers consider these customizations, as they could cause unexpected behavior or even break Firefox. Firefox is a work in progress and, to allow for continuous innovation, Mozilla cannot guarantee that future updates won’t impact these customizations.

Mozilla does not officially support adding custom style rules with a userChrome.css or userContent.css file, or using the Configuration Editor (about:config page) to modify preference settings.

If Firefox suddenly appears broken after an update, you may need to use the Refresh feature to restore Firefox to a default state while keeping important data. Alternatively, you can selectively reverse your advanced customization and configuration changes, as follows:

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