In my never ending quest to find the best tool to debug ajax applications, I came across a lot of cool extensions that you can add to Firefox to make it more ajax-debug-a-rific.

First, there's Venkman. It's a more or less advanced version of the Javascript console that comes with Firefox. If you're going to be using Venkman though, you might just want to jump straight to an extension called FireBug. This extension rules hard. It has a command line appearance that is able to list all javascript and CSS errors. More importantly though, it's able to show you the content of XMLHttpRequests. This makes it incredibly easy for AJAX debugging.

Finally, there is a tool called TamperData which lets you track and modify HTTP requests. Basically you can change the data that is sent to the webserver on the fly. It's kinda akin to an HTTP Proxy that some individuals use to probe for vulnerabilities in web software.

Here are the links for the three I just mentioned.