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