I have tested with and without that ome.iehacks.css and I do not see any difference in IE9. I am not sure about usage of that as is only IE9 specific https://github.com/openmicroscopy/openmicroscopy/blob/develop/components/tools/OmeroWeb/omeroweb/webgateway/templates/webgateway/viewport/omero_image.html#L37. Removing that file for now