Firefox
Firefox is a web browser.
Installation
Most Linux and BSD distributions offer a firefox package. Some also offer a firefox-nightly package with the experimental development branch. The self-updater will be disabled.
On Windows, download directly from Mozilla's website. Firefox will self-update on launch.
Configuration
Behind-the-scenes configurations are made at about:config.
Interface Themes
The browser interface is customized through themes which can be installed either from Mozilla's registry or from a file.
Dark Mode
A web browser's support for dark mode is broken into two components: the browser interface and the web content.
Firefox tries to match a system preference for light and dark mode and enforce that over both components. In lieu of a recognizable configuration, Firefox defaults to light mode. If the user explicitly sets a dark-colored theme (such as the built-in 'Dark' theme), Firefox reads this as an explicit dark mode configuration.
If the browser interface is configured for dark mode (either implicitly or explicitly), it enforces that over web content as well (using prefer-color-scheme in the user agent). (See here for design rationale.) In order to force Firefox to use light mode for web content irrespective of browser interface theming, set privacy.resistFingerprinting]] to true in about:config`. (See here for design rationale.)