@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);
#searchbar [empty="true"]:not(:hover) .searchbar-engine-button {
visibility: hidden !important;
}
#searchbar [empty="true"]:not(:hover) .search-go-button{ 
display: none !important; 
}
#searchbar [empty="true"]:not(:hover)
{
color: transparent !important;
}