Using Firebug in IE, Opera, Safari

Most people know about Firebug, as a plugin to Firefox... but you can also debug javascript in other browsers with Firebug, by installing Firebug Lite.

http://www.getfirebug.com/lite.html

It's awesome to include a .js file, open up Internet Exploder, and use alot of the Firebug goodness to check browser compatibility. (after test, or prior to loading to your production webserver, simply comment out that line of .js and you won't take a hit when it comes to page load times).

Here is some more Firebug documentation and references from their site:
http://www.getfirebug.com/docs.html

Core Javascript & Ajax Development Links

...some handy references for all of us writing Javascript and Ajax apps (specifically with Prototype.js, but many of the links help writing and testing JS in general) Enjoy:

Core Javascript 1.5 Reference
http://developer.mozilla.org/en/docs/Core_JavaScript_1.5_Reference

Javascript Style Guide on Mozilla's Development Center:
http://developer.mozilla.org/en/docs/JavaScript_style_guide

Prototype Javascript Framework API docs:
http://www.prototypejs.org/api

Script.aculo.us Effects Library tag docs:
http://wiki.script.aculo.us/scriptaculous/tags/

Dan Webb's LowPro.js:
http://www.danwebb.net/2006/9/3/low-pro-unobtrusive-scripting-for-prototype

Joe Hewitt's Firebug plugin docs and download:
http://www.getfirebug.com/docs.html

https://addons.mozilla.org/en-US/firefox/addon/1843

Selenium:
http://www.openqa.org/selenium/

Firebug, Joe Hewitt; (high rez screencast from YUI Theater)

...Firebug is an unbelievable Javascript tool -- for creating, experimenting, and debugging Javascript. Check out Joe Hewitt's presentation: