Actually, you can specify with the moz-radius or something operater to round the corners.... so you can use that as an IE only CSS style, and then use the moz-round or something to do that in Mozilla.
Use the following to hide from IE:
Code:
/* Hide Following Code From IE/Mac \*/
/* */
To hide from IE/Win you have to use the selector class (* or >) so you have to specify the parent element...