I see the problem, and even on viewing initially in Firefox there seems to be a minor issue with the text alignment.
I also note that there's been some modification of the search field's CSS which may have come from use of a plugin, or from direct customization.
If you've added a form plugin, could you deactivate it temporarily, refresh and see if the problem still exists?
Just to explain why IE and not the others... IE does not recognize some CSS3 and HTM5, so it sometimes behaves quite differently than other browsers. Once we can identify the source, we can find a cure.