Its the problem with browser compatibility.IE - WorksFF 15 and FF3.6 doesnot work as expected.
In edit mode we need to have separate CSS as we do the content authoring in desktop browser (IE or FF). But there is no method I found till now to replace this edit mode CSS with actuall CSS (in preview or final HTML) as we donot want it tobe included in the final HTML. Due to performance issue we cann't keep unnecessary files in the actual HTML, inspite what so ever the size it is.