The Eternal IE vs FF struggle

Alright, after days of grueling battle I’ve finally got a DHTML/CSS menu that’s truly crossbrowser and capable for business.

(yes, I gave up on a true CSS menu when I discovered that Dropdowns and Tables don’t mix - ouch!
NOTE TO SELF: The next site will be 100% CSS driven.)

So, I’ve got this menu and it’s pretty good…
except FF is throwing one single pixel into the mix that’s throwing off my chi!
The background on the dropdown is one pixel to big - it’s overlaying the border?!?!?

Check it: www.cuush.com

Can anyone enlighten my humbled mind with the fix for this?
I’ve tweaked everything on the sheet to no avail (including the !important hack on the width).
I’m stumped - and the stumpgrinder’s broken.