The theme and general feel of the design is very nice. The positioning appears to be weird in FF, but you knew that.
About the content... I'm not really a fan of the submenus you have. It'd be a lot easier to use the page if you just put your links inside your boxes on the right side. It also breaks copy + paste.
I really like how your menu sidebar looks, but I think it would look better if it extended farther down the page. For that matter, I think the whole thing would look and function better if it used the full size of the page. Your header tree thing would work better if it was on the right extreme of the window.