Web Forms :: NavigationMenu Dropdown Submenu Not Visible In IE & Chrome?

After launching my first ASP.NET site (www.oldfutures.com), I have noticed that the dropdown menus of my NavigationMenu web server control don't appear in Internet Explorer or Google Chrome... however, they show up and work fine in Firefox. Looking at the page source I found the following line that I think might be responsible:

.ctl00_NavigationMenu_0 { background-color:white;visibility:hidden;display:none;position:absolute;left:0px;top:0px; }

I have noticed that all of the menu items with submenus include a tag for ".ct100_NavigationMenu_0", and all of the submenus don't appear as they should. They simply appear white, and none of the options of the submenus function. The problem is that I don't know where that code is being generated from. I can't find any settings where that is set up. It must be generated by ASP.NET 3.5, but I don't know where from, nor how to change it. Is this line indeed the problem? If so, how do I fix it? Is there some other line in there that is the problem? I've been trying to figure this out for a while and feel like I'm beating my head against a wall. Could anyone take a quick look at my site and see if you can figure it out, or at least point me in the right direction?