I can easily set breakpoints in embedded JS functions, but I don\'t see any way of accessing external JS scripts via Firebug unless I happen to enter them during a debug ses
After you place a break point in them, you can also call them by name in the firebug console, and see the output of (or step through) any intermediate functions. This can help when the main entry point calls many other helper functions, and you are really just concerned with how these helpers are working.
That being said, I don't knwo anything about ASP.Net validators, so its possible this doesn't apply.
Place debugger; in your external script file on the line you want to break on.
Clicking on the line number in the left hand margin should create a break point for you (a red circle should appear).
All loaded scripts should be available from the firebug menu - click where it says the name of the current file should show a drop down with all files listed.
Putting the "debugger;" line also does the trick for the Chrome debugger.
To view and access external JavaScript files (*.js) from within Firebug: