Web Developer Extension for Firefox is an extremely useful add-on for Firefox that allows web developers to analyze the compete structure of the page, including elements like CSS style sheets, forms, cookie data, ID and Class details, Java Scripts, images and much more. It also allows you to edit the current style sheet of the page and see the effects in real-time, load a user defined style sheet, or disable styles altogether. The extensive outlining options allow you to visualize the CSS and HTML elements of the page by outlining tables, DIVs, frames or any other element that you define. You can also view form input data along with field names and values and manipulate forms for testing. Other features include links to online code validations, browser window resizing, source viewer with syntax highlighting and more.