function mainWindow(){
    var mainwindow = window.QueryInterface(Components.interfaces.nsIInterfaceRequestor)
    .getInterface(Components.interfaces.nsIWebNavigation)
    .QueryInterface(Components.interfaces.nsIDocShellTreeItem)
    .rootTreeItem
    .QueryInterface(Components.interfaces.nsIInterfaceRequestor)
    .getInterface(Components.interfaces.nsIDOMWindow);
    return mainwindow;
}