I'm sorry to be blunt, but it doesn't look good in Firefox. In Safari your menu is being stretched, but in Firefox the Make An Appointment option is being wrapped down.
You have 3 validation errors in your code. Line 67, 97 and 108, the align attribute does not exist for those elements.
You also have invalid CSS code at the beginning of that document with style2, style6 and style8. All CSS declarations need to have attribute:value; . In your case the values are not valid. 12 is not a valid font-size. When you declare font-sizes you need to have a unit of measure following them whether it is pt, px, em, etc. Same thing goes for a:hover on your other CSS document. A color needs to start with a "#" in front, otherwise the browsers will ignore the color.
To fix your div issue I would probably say to remove the outer margin. You already have padding within the cells, so it was like having double padding on the sides. Otherwise you will need to reduce the font-size for that area to make it work, unless you create a fixed or percentage-based width for the menu options thus forcing text to wrap within those containers.
Since you on Mac, check out the Safari development site at Apple: https://developer.apple.com/safari/
You might have to create a developer account (the basic level one is free). Tons of excellent info on Safari there. You can do much with that browser.
Firefox's dev center is at https://developer.mozilla.org/En Another excellent resource for another great brower.
IE , well IE's a mess. But I suppose we all must deal with it.. so... http://msdn.microsoft.com/en-us/ie/default.aspx
Just some "light" reading.