I'd recommend approaching this problem from the other end.
Copy your current IE-only stylesheet to a global stylesheet, and put the IE stylesheet into a conditional comments block. Fix the site for Firefox using the global stylesheet, and then use the IE-only stylesheet to fix the site for IE.
Eg:
<link href="/css/global.css" rel="stylesheet" type="text/css" />
<!--[if IE ]>
<link href="/css/ie-only.css" rel="stylesheet" type="text/css" />
<![endif]-->