titlebar = { yes | no | 1 | 0 }
Specifies whether to display a Title Bar for the window. The default is yes.
Internet Explorer 5.5 and later.
This feature is no longer supported. The Title Bar remains visible
unless the fullscreen sFeature is active.
Thus, you need:
fullscreen = { yes | no | 1 | 0 }
Specifies whether to display the browser in full-screen mode. The default is no. Use full-screen mode carefully. Because this mode hides the browser's title bar and menus, you should always provide a button or other visual clue to help the user close the window. ALT+F4 closes the new window.
For full details read here:
Window.open Method[
^]