The real use of this property is to access its visible property.
window.menubar.visible
If it is visible, the property returns true. It returns false if the bar is not visible.
<html>
<script language="JavaScript">
<!--
document.writeln('<h3>Browser Chrome Status</h3>')
document.writeln('Menu Bar: ' + window.menubar.visible + '<br>');
document.writeln('Tool Bar: ' + window.toolbar.visible + '<br>');
document.writeln('Location Bar: ' + window.locationbar.visible + '<br>');
document.writeln('Personal Bar: ' + window.personalbar.visible + '<br>');
document.writeln('Scroll Bars: ' + window.scrollbars.visible + '<br>');
document.writeln('Status Bar: ' + window.statusbar.visible + '<br>');
document.close();
-->
</script>
</html>