thindenim
As I mentioned earlier, specifying the width of the subnavbar li helps with this situation.
See
IY e-solutions -girlznight test
where I have mocked up the menu. Style info is at top of page.
Two additions to your style (and addition of wrapping <u></ul>)
Using float:left does not work in FireFox as you need to specify the height of subnavbar <u>. Unfortunately, this also limits the number of menu items that you could have, unlike your option which would, if you wished allow a third layer.
Cheers
Ian