- Enable Script Debugging (both IE and Other) in Internet Explorer.
- Disable friendly HTTP messages in Internet Explorer.
- Enable Display a notification about every script error in Internet Explorer.
- Start your WebBrowser-embedded application without debugging (Ctrl-F5).
(Posted here so I don't forget the steps.)
(This was abstracted from many sources including Silverlight 4 Tools for Visual Studio 2010 Debugging Overview.)