i've had this site up for awhile, and suddenly today that front page tabbed area is all skewed in firefox. Same thing happening on the french version of the site http://www.brysonfarms.com/francais/
(both these are joomla 1.5) and same thing for a fresh install at http://www.brysonfarms.com/seeds
(i was just about to create a ecommerce part of the site).
For me it's also happening with your demo