According to the specification.
Authors specify the style and location of generated content with the :before and :after pseudo-elements. As their names indicate, the :before and :after pseudo-elements specify the location of content before and after an element's document tree content. The 'content' property, in conjunction with these pseudo-elements, specifies what is inserted.
:before and :after should only work on the element which can act as a container of content. <input> cannot contain any content so it should not support those pseudo-elements. Chrome supports because it does not follow the spec (or bug?).
