Just been looking at the css issue.
I think its down to IE and Firefox treating things like the "padding" and/or "margin" paremeters differently. I think one of them puts them inside the "width" you specify, and one outside.
I have had a play with the stylesheet, and found if you set the "thumbnail" class as follows, it looks fine in both browsers...
PADDING-RIGHT: 10px; PADDING-LEFT: 10px; FLOAT: left; PADDING-BOTTOM: 10px; MARGIN: 15px 19px; WIDTH: 122px; PADDING-TOP: 10px; HEIGHT: 130px; TEXT-ALIGN: center
Basically, before you had the "width" set to the same width as the image width, and then I think IE was adding the padding/margin to the inside of the divs...
Not 100% sure of the ins and outs, but the fix I've done seems to work for both browsers!