I can try to break down your code for you, which might help lend some understanding.
I think what you have here:
Is referencing your "mm_menu.js" file, which is loaded here:
Then I believe you reference a function within that .js file by initializing the function here:
Last but not least, this activates your menu:
If you'd open your .js file, you'll probably see a function in there called MM_nbGroup('out'); which is doing the mouse out switch.
Anyway, just a stab in the dark, I don't have or use Fireworks, but that's what seems to be happening.
Nice site, btw. Very tactile.
This is probably counting how many people are coming to your site, at least it seems like that by the way it's implemented at the bottom of your page:
what is this?