this generally is a result of your css coding. Making a consistent look across ie & FF is often frustrating and requires some additional work. The guys at AC have been able to do a lot of these corrections for us in the past until we brought someone on internally with this type of cross browser compatibility experience. If you still need help (after getting a quote from AC to fix css, which I suggest) send me a private message; my team may be able to help.
-Brian