Seems like every day there’s a cool new Firefox add-in to aid in development. The latest is Firebug. This cool utility lives in the browser’s statusbar, monitoring each page you visit for problems. It reports what you tell it to report: JavaScript exceptions, CSS errors, XML errors, and more! It even peeks in on XMLHttp requests so you can see exactly what is going to and coming back from the server. Want to learn more about a particular element? Click the Inspect Element button, click on the element in question, and FireBug provides you with its raw code, all style sheet information, and all the JavaScript properties and methods for it.

Currently, it’s only available for Firefox 1.5 and higher, so you’ll need to upgrade your browser if you haven’t already. But still, this little gem can help you with your debugging in ways you never thought possible.