Firefox & Mac Browser Errors

I have recently developed a website using WordPress for my restaurant The Black Crow. http://www.theblackcrow.com/wordpress/ the layout is a .css variation of the blix theme.

It looks great in IE on the PC but the navigation section at the top below the header completely falls apart in Fire fox PC & on the MAC browsers Safari and IE.

The navigation squishes together an is no longer legible.

Can you please advise as to how I might remedy this problem.

Thanks for the insights.