FireBug
Sloshing around in rails and playing with AJAX is fun and all, but we hit a roadblock the other day when trying to view the html source of AJAX rendered components. You can't just hit cntrl-u in Firefox to see the source. After some googling, FireBug is the tool that rocks.
Not only is this helpful for debugging web applications, but it'll help when performing web assessments. I particularly liked the feature which highlights the elements on the html page when you select the corresponding code in the FireBug console.FireBug lets you explore the far corners of the DOM by keyboard or mouse. All of the tools you need to poke, prod, and monitor your JavaScript, CSS, HTML and Ajax are brought together into one seamless experience, including an error console, command line, and a variety of fun inspectors.
