possible MenuBar bug - request for confirmation

Hello,

In my application I'm having this problem with MenuBar not being displayed properly on Firefox (13.0 at the moment of writing). I would prefer to get a confirmation from another person before filling in a bug report. Could you please test this sample code on your Firefox?

To reproduce this problem you have to move your mouse cursor to the "four" item without going through "three" first, in other words you can't approach it from the top. So move your mouse cursor to "five" and then up to "four". I have also noticed that it is somehow related to the number of items in MenuBar i.e. adding or removing some items can "fix" the problem. With default white background these artefacts are barely visible.

Here is the sample code:

Window mainWindow = new Window("MenuBarBug");
setMainWindow(mainWindow);
        
VerticalLayout rootLayout = new VerticalLayout();
rootLayout.addStyleName(Reindeer.LAYOUT_BLUE);
rootLayout.setSizeFull();
mainWindow.setContent(rootLayout);
        
MenuBar menuBar = new MenuBar();
rootLayout.addComponent(menuBar);

final MenuBar.MenuItem file = menuBar.addItem("File", null);
file.addItem("one", null);
file.addItem("two", null);
file.addItem("three", null);
final MenuBar.MenuItem sub = file.addItem("four", null);
file.addItem("five", null);

sub.addItem("A", null);
sub.addItem("B", null);
sub.addItem("C", null);
sub.addItem("D", null);
sub.addItem("E", null);

Please note that it affects Firefox only and you have to move your mouse in a specific way.