Script Runner is a Firefox add-on tailored for web development that allows users to customize their browsing experience by adding custom JavaScript and CSS to websites. With a user-friendly interface, it enables easy management of scripts specific to individual sites, ensuring they are automatically applied during each visit. Additionally, users can create global scripts that function across all websites, streamlining the customization process and making web interactions smoother.

This add-on also simplifies access to the console through its convenient dropdown menu, allowing users to input and save their JavaScript or CSS codes effortlessly. This feature is particularly beneficial for both developers and casual users aiming to enhance their web experience. Overall, Script Runner is a practical tool for anyone looking to personalize their Firefox browsing experience.