AJAX Lesson #2 - Javascript debugging

Lesson #2 that I have learned with Javascript is that you need to be able to debug your javascript.  Get some good javascript debugging tools?  Microsoft had the script debugger at one time.  I never liked the Interdev or VS.NET javascript debugging, but I didn't work with them much.  I believe that Netscape had a pretty good javascript debugging tool at one time.  I'm going to go check the mozilla site for a javascript debugger.  Can you recommend a javascript debugger?

Wally