Double check your syntax. FireFox is more forgiving of errors than IE when it comes to the CSS code. For example:
[sourcecode language="css"]background:transparent url(images/check.gif)no-repeat 0 6px;[/sourcecode]

Will work as intended within FireFox but not IE even though there is no space between the URL declaration and the “no-repeat” parameter. Change that code to:
background:transparent url(images/check.gif) no-repeat 0 6px;
And it will work fine all around.