JavaScript debugger needed.

Can anyone recommend a decent JavaScript debugger? What I need is something to find possible blind spots making it work it Internet Explorer or Opera, but not in Netscape Navigator or Phoenix.

I thought about adding type="application/x-javascript" to the external script line in HTML head, but after that edition, Internet Explorer started returning errors of the "object required" type. I guess it must be a problem with meeting some standards then. The script is very long, 70KB, so it's practically impossible to look through it and find it, especially because the line numbers supplied by IE error messages actually lead to empty lines (line 1272 is in the middle of a few empty lines, even). Perhaps it doesn't count empty lines as lines and thus in fact leads to completely different places than it appears to. The script is to be found here and the page using it is http://www.chevalier.szm.com/rptest.html. I've also created a large, over 130 KB page, including the script as an internal one. That page is http://www.chevalier.szm.com/nnrptest.html. Still doesn't work. Nor does it return any errors. As though it lead to a nonexistent function.

Thanks in advance for any help.