Closing first browser window

When I load my first ASP.NET application page in the browser, I want to transform the browser window by removing toolbar, menus and status bar. As I can’t do that, I open another window without these controls, but then I cannot close the first window without the messagebox which warns the user that the window will be closed. Is there any possibility to close the first window without the messagebox, or to “clean up” the first window while loading ASP.NET page?