You would think the answer is "Of course!" After all, you pay good money to smart designers to make sure it does.
So, I was nearly incredulous when I discovered that the Clos du Val website didn't work properly in either Chrome or Firefox.
It works fine in Internet Explorer (IE), though.
Here are the screen shots (click the thumbnail to see full size).
Chrome (menu is visually busted, although it does "work"):
Firefox (menu is not visible at all, which means you can't navigate):
Internet Explorer 8 (why do people think there's a problem?):
Nowadays, it's quite easy to install all three browsers on your system (unlike the old days, when IE seemed to go out of its way to make other browsers malfunction), so even if your web designer says everything works, you can (and should) check for yourself.
The moral of the story is "trust but verify." I'm sure Clos du Val has been happily thinking that everything is fine with their website. In reality, somewhere between 20 and 50 percent of their visitors aren't able to access it as intended.