How does one go about debugging javascript?

Do you use firebug and run your page through your localhost?

If javascript is part of an ASP.NET application, I have found that the breakpoints in a .js file in Visual Studio seem to be ignored.

The problem I see is that the ASP.NET application which uses javascript code has too versions -- a published and a debug version. The Debug version is located within my group of folders under the localhost. Also, when I launch the program through Visual Studio, it defaults to IE. Is there some way I can have it launch a different browser that will allow for javascript debugging?

Is there a step-by-step description somewhere?

Javascript seems to be very popular. I imagine a debugger is in use. So, what is it and how can you use it if your javascript is already part of an web site/page?