Here is the generated code of the div which hide the jscookMenu with IE (not with Firefox).
<div style="position: relative; width: 1268px; height: 812px; top: 0px; left: 0px;" id="content"><!--Map Control Renderer Start (map1)-->
<script type="text/javascript" language="Javascript" src="/Project/js/esri_map.js"></script>
<div id="EsriMapCell_map1" style="width: 488px; height: 370px;">
<div style="overflow: hidden; width: 1268px; height: 812px;" id="MapDiv_map1"><div style="overflow: hidden; position: relative; width: 1268px; height: 812px;" id="MapControlDiv_map1">
<div style="position: absolute; left: 0px; top: 0px; width: 1268px; height: 812px; cursor: move;" id="MapGridDiv_map1">
<img style="border: 0px none ; margin: 0px; padding: 0px; position: absolute; left: 0px; top: 0px; width: 1268px; height: 812px; z-index: 1; opacity: 1;" class="esriMapImage" id="MapTile_map1_mapSource1_0_0"
src="/Project/mimedata;jsessionid=2EC77F099921C273D85AAC9EEF610EAC?wname=esriWebSession&id=map20142043&uniqueId=15">
<div style="border: 0px none white; overflow: visible; position: absolute; left: 0px; top: 0px; width: 1268px; height: 812px; background-color: transparent; z-index: 19;" id="MapGraphics_map1_gc"></div></div>
<img style="display: none; z-index: 99;" class="esriLoadingImage" src="images/loading.gif" id="MapLoading_map1"></div></div></div>
</div></div>
<input name="mapForm" value="mapForm" type="hidden">