layered masking of screen using css and iframe

this works for mozilla---
<div id="searchPanelCursorDiv" style="background-color: #D0D0D0; border: 0 none; height: 100%; left: 0; margin: 0; opacity: 0.5; padding: 0; position: fixed; top: 0; width: 100%; z-index: -200;"></div>