I took the screen shots of all three environments and here is what I got for heights (using Photoshop):
Cute Editor:
Div (including borders): 332px;
Div (without borders): 326px;
IE 6:
Div (including borders): 338px;
Div (without borders): 332px;
FireFox 1.5
Div (including borders): 338px;
Div (without borders): 332px;
Which is exactly what I described, and exactly what the three screen shots show.