Debug CSS is a lightweight extension designed for Mozilla Firefox that enhances web development by adding outlines to all elements on a webpage. This tool is particularly useful for developers looking to identify how different elements interact and affect the layout. By simply holding the Ctrl key and hovering over any element, users can view detailed information about the element along with its CSS values, making it easier to troubleshoot layout issues during development.

Installation is straightforward; users can toggle the extension on or off by clicking the icon or using the keyboard shortcut Alt+Shift+C. Debug CSS simplifies the process of visualizing elements on a page by applying a unique outline color to each element, differing from the standard red outline that can be added through traditional CSS. This feature allows for a clearer understanding of element positioning and interactions.