Firebug is a browser add-on that allows us to analyze the inner components of a web page, such as table elements, CSS classes, and frames. It also has the ability to show us DOM objects, error codes, and request-response communication between the browser and server.

In the previous recipe, we saw how to look into a web page's HTML source code and found a hidden input field that established some default values for the maximum size of a file. In this recipe, we will see how to use the browser's debugging extensions, in this particular case, Firebug for Firefox, or OWASP Mantra.