Owl - Dark Background is a Firefox add-on designed to improve the online reading experience by transforming webpages into a dark mode. This tool is particularly beneficial for users who spend extended periods on their computers, helping to reduce eye strain caused by bright backgrounds and harsh color contrasts. With Owl, users can enjoy a darkened background paired with lighter text, making content easier to read and navigate.

The add-on offers several features including syntax highlighting for code snippets and the ability to quickly toggle the dark mode using the Shift + Alt + D shortcut. Users can choose between two themes, the Classic and the new Inversion theme, disable the add-on on specific websites, and set it to activate automatically upon Firefox startup. Additionally, it allows for easy management of themes on a site-by-site basis, providing a customizable browsing experience.