Conditional Comments to butcher it up for IE9. Without seeing all the HTML and CSS, I can't even begin to guess whether it's a basic incompatibility problem that can't be worked around or just some code you wrote that won't work in both 9 and earlier versions. But using conditional comments will fix the problem, if in a very inelegant way. (But then, the inelegance is really Microsoft's, in choosing to march to the tune of a different plumber.)