Doing Java development in Eclipse, I have learned how wonderful it is to have a good debugger. I had wished for something similar for the browser, to help debug HTML and Javascript. My desires have been answered as Firebug. Go to the Firebug home page and just browse through the list of features. It is a wonderful tool and a great debugger that runs as a plug-in to the Firefox browser. Being able to figure out what someone else’s code is doing by identifying the Ajax calls and looking at the HTTP requests and responses and headers has saved me a lot of time. If you are doing anything that is browser-based, Firebug is a must-have. And being free, there is no excuse not to have it.