- You should have properly installed Java Plug-in (see http://www.javasoft.com/products/plugin/).
- Start Java Plug-in Properties (On Windows: Start/Settings/Control Panel/Java Plug-in).
- Check Enable debug on Advanced tab and press Apply.
- Convert your ".html" files to the format used by Java Plug-in (see http://www.javasoft.com/products/plugin/1.3/docs/htmlconv.html).
- Open html page with applet in Netscape/Internet Explorer.
- Open "Attach to VM" dialog from NetBean?'s toolbar or menu Debug. Enter the value from Java Plug-in/Connection Address field ("4025") to the "Name" input line in Attach to VM dialog and press OK.
- NetBeans debugger should be connected to the VM used by Netscape/IE now.
Java Plug-in threads and thread groups can be accessed from Debugger Window/Thread Group's tab and debugger should be ready to stop on breakpoints.
For details on applets, see the NetBeans IDE 4.1 Tutorial for Applets.
Source: NetBeans User FAQ