Debug does not work in Silverlight project
Even if you run the Silverlight project in debug mode from Visual Studio, debugger does not attach to the process of your browser. Why? Because I was using Firefox!
At least, Silverlight team could pop-up a notification window which says "you should use IE to debug your project". Come on, I lost 20 minutes for this.
Therefore, for the ones who cannot debug Silverlight projects, try to debug it with IE. (mine works with IE 9 and does not work with Firefox 3.6)