Quick review how a silverlight application work in browser
1. The user requests the HTML entry page in the browser.
2. The browser loads the Silverlight plug-in. It then downloads the XAP file that contains your application.
3. The Silverlight plug-in reads the AppManifest.xml file from the XAP to find out what assemblies your application uses. It creates the Silverlight runtime environment and then loads your application assembly (along with any dependent assemblies).
4. The Silverlight plug-in creates an instance of your custom application class (which is defined in the App.xaml and App.xaml.cs files).
5. The default constructor of the application class raises the Startup event.
6. Your application handles the Startup event and creates the root visual object for your application.