Eliminating Prompt, when using command to close a browser window

Hey!

I am using this command to close a window in flash ms 2004:

MyButton.onRelease = function ()
{
getURL("javascript:window.close();");
}

But when , I click the button that executes this command, it prompts a window asking me if I’m sure I want to close the browser. How can I eleminate this prompt?