Apparently there seems to be a problem on Firefox when you want to specify a size for a
file-upload box (which is an HTML input control of type "file"). If you just specify the width as style tag it will (surprisingly ;) ) work with IE but for some reason not with Firefox.
The solution to this problem is to specify a "size" attribute like:
<input type="file" id="someId" name="someName" size="10"/>