Jello wrote:

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 a debugger, an error console, command line, and a variety of fun inspectors.

Visit the FireBug website for documentation, screen shots, and discussion forums:

http://www.joehewitt.com/software/firebug/

A quick overview of FireBug's features:

* JavaScript debugger for stepping through code one line at a time
* Status bar icon shows you when there is an error in a web page
* A console that shows errors from JavaScript and CSS
* Log messages from JavaScript in your web page to the console (bye bye "alert debugging")
* An JavaScript command line (no more "javascript:" in the URL bar)
* Spy on XMLHttpRequest traffic
* Inspect HTML source, computed style, events, layout and the DOM

Works with:
Firefox 1.5 - 3.0 ALL

I was very frustrated doing AJAX/AHAH development until I found this tool.

No doubt.

Firebug lets me inspect any part of the DOM I want, and it lets me look at the XMLHttpRequest and its response.

Its true, this plugin lets you dig down into the DOM in a way that other plugins like Web Developer or Venkman won't allow. I particularly like the way you can enter the DOM either by pointing directly at the element on the page or start from the root node in the DOM browser and work your way down. From there you really do have the entire DOM to work with, not simply a tree of HTML elements and attributes.

Pretty damned cool.

I must agree. This is worth checking out if you're doing JavaScript development, especially if you've been feeling somewhat limited by the capabilities of other plugins.