@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);

#urlbar[level="high"] > .autocomplete-textbox-container
   { background-color: lightgreen !important; } 

#urlbar[level="low"] > .autocomplete-textbox-container
   { background-color: yellow !important; }

#urlbar[level="broken"] > .autocomplete-textbox-container
   { background-color: red !important; }