in the screen.css file, add position re;ative to the #footerMainNav and #sitemapNav classes, and give a low z-index to the #sitemapNav and a high z-index to the #footerMainNav:
#fullWidthFooter #footerWrapper #footerNavigation #footerMainNav {
height: 30px;
position: relative;
z-index: 999;
}
#fullWidthFooter #footerWrapper #footerNavigation #sitemapNav {
clear: left;
height: 30px;
position: relative;
z-index: 1;
}