I'm not sure I understand what you mean but I only see one thing... doesn't fit with what you say about a background image though...
Those boxes where it says "September specials!" and "New Products!". They are run together in Moz but have a nice margin between them in IE. Is that what you mean?
If so, the "margin" is created by a BR tag. That doesn't give you the extra space in Moz. Delete the BR (and also a </b> that's on the loose there). Then use CSS. :)
Something like so should do it:
.item-contain { margin-bottom: 10px }
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