This looks like bug 222482. See bug 222482 comment 2
Actually, we just went ahead and made it impossible to show the hidden input, because people apparently don't stop and think about what their CSS rules mean...
In Firefox 3.5.3 setting the display property of the INPUT element to a value like 'block' or 'inline-block' will cause hidden inputs to be displayed
Right; bug 436046 is fixed in the Firefox 3.6 alpha and later.