--- a/toolkit/themes/shared/in-content/common.inc.css
+++ b/toolkit/themes/shared/in-content/common.inc.css
@@ -648,16 +648,21 @@ xul|listbox xul|listitem[selected="true"
 /* Trees */
 
 xul|tree {
   -moz-appearance: none;
   font-size: 1em;
   border: 1px solid #c1c1c1;
 }
 
+xul|tree:-moz-focusring,
+xul|richlistbox:-moz-focusring {
+  border: 1px dotted #0095dd;
+}
+
 xul|listheader,
 xul|treecols {
   -moz-appearance: none;
   border: none;
   border-bottom: 1px solid #c1c1c1;
   padding: 0;
 }