The first picture is IE, the second picture is Firefox. Both of these are on Windows.
The problem is that the blue box is big and puffy in Firefox, and not so in IE.
Does anybody whose CSS knowledge is better than mine tell me how to make those look closer alike? I don't really care whether the blue box is puffy or thin (I slightly prefer the puffy box, but I'm more concerned about making them look similar.)
The page in question is the page linked in my prior entry and here.