In short, Internet Explorer is a sub par browser when compared to Firefox and Chrome. We do our best to make sure our menus are functional in Internet Explorer, but there are some instances our menus do not look perfect in IE.
Currently our menus are built to work with Internet Explorer 8,9, and 10. We have dropped support for Internet Explorer 6 and 7 a while back due to the lack of proper support for CSS. Internet Explorer has come a long way in the last couple years towards properly supporting CSS standards, but even IE 8 and 9 still have some poor support for some of the newer CSS options.
That being said, if your menu is not displaying correctly in internet explorer, try some of the solutions below:
IE Quirks Mode
Add this little bit of code somewhere between your HEAD tag.
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1" />