With a page as simple looking as that, there is no reason why you need to use absolute positioning. Without absolute positioning, elements are very unlikely to overlap. If you want to keep absolute positioning, one trick is to use the !important hack:
FF will follow the 325px positioning and IE will use the 305px one. Unfortunately, Opera (the other pc browser) will follow the 325px style but renders more like IE. Not too many folks use Opera though. Yet, another reason to avoid absolute and relative positioning. Save those for special cases. Use padding and margins, widths and heights to get the spacing you desire.