The first thing I would do is fix the validation errors as any one of them could trip Firefox up.
Especially the section concerned as you have an invalid structure than Firefox may be ignoring.
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You have wrapped anchors around block elements which is invalid (ouside of html5) and has been known to cause browsers to render things incorectly. The anchor should be set to display:block and the inner p elements should be changed to a inline element such as a span although you can still style them to behave like block elements etc.
My debugging always starts with step 1:
1) Validate the page and rule that out as a cause
2) Isolate the problem
3) Fix it