I've still got to figure out why the left table isn't getting pushed up to the top, I could've sworn I had that working at one point. Probably broke it getting Opera to work on the
right table...
Your home link isn't in an actual list, you should probably just remove the <li></li> tags from around it, since it's making a floating bullet in Firefox (looks fine in Opera, which is probably why you didn't notice it).

Well, that was simple. I forgot
vertical-align: top; in td.content. Open ff4snes.css and add the line, like this:
td.content{
width: 75%;
height: 100%;
vertical-align: top}Should solve that issue. Now I remember, I originally had vertical-align on the table itself, rather than the table cells that draw the content and menu. When I was fighting with Opera I must've figured out that it was just pushing the table to the top, rather than their content, and pulled it from there and stuck it in the menu. I just forgot to add it to the content class.
Also, I can't validate your page anymore. I think your copyright symbol in the footer is to blame, actually. Replace it with
© and see if that works:
Validator