I remember using something in Netscape that was able to debug JavaScript code in webpages, must have been in 2000 or so, maybe in Netscape 4. Don't remember if

I remember using something in Netscape that was able to debug JavaScript code in webpages, must have been in 2000 or so, maybe in Netscape 4. Don't remember if it was built in or not. Anyone remember what it was called?