Mozilla is a global, not‐for‐profit organization dedicated to improving the World Wide Web. They have an international community of developers who contribute to open-source software.

Mozilla’s most popular open-source project is Firefox, the second most used web browser globally. Its most recent release, Quantum, includes new styles, features and ways for users to customize the appearance of the browser.

Users are reluctant to switch internet browsers once the browser has been personalized to their liking. Previously, themes only had the ability to alter the appearance of the default toolbars and tabs.

Our Dark Theme Darkening increases the customizability of Quantum to include menus, popups, settings pages, loading indicators, sidebars, icons and added theme transitions. Additionally, Google Chrome themes can now be imported directly into Firefox.

The default Dark Theme is updated to reflect the new additions. Extending theme support in the browser gives theme developers more power to express their creativity, and gives users more surface area on which to enjoy themes.

In the screenshots to the right, one can see the current un-themed sidebar and settings page in the background, while the foreground shows the same content themed.

Our Dark Theme Darkening is implemented using CSS and JavaScript, and impacts hundreds of millions of users.