css menu problem only in firefox

Theme = Twenty Ten
URL = yoursocrates.com

In Appearance > Edit CSS I added this to add color to the menu items on hover:

#access li:hover > a,
#access ul ul :hover > a {
	background: #b80000;
	color: #fff;
}

It works fine in Safari and Chrome, but the submenu is a problem in Firefox. On hover the color changes and the submenu appears, but moving the mouse to the submenu makes it disappear again.