Softminer.net

Usually firefox has some extensions for debugging javascript.

to debug javascript in visual studio asp.net 2008 do the following steps:

Enable client-side script debugging in Internet Explorer
1.Open Microsoft Internet Explorer.
2.On the Tools menu, click Internet Options.
3.On the Advanced tab, locate the Browsing section, and uncheck the Disable script debugging check box, and then click OK.
4.Close Internet Explorer.

In your JavasSript function add the keyword debugger .
like this

debugger;

This causes VS.NET to switch to debug mode when it runs that line.

Run your ASP.Net application in debug mode.

PS: SLint.VS is Add-In for Visual Studio that provides errors in JavaScript during compiling enabling you to spend less time in browser catching bugs and typos.

http://www.codeplex.com/jslint