the *REAL* fix for misbehaving drop-down lists. turns out z-index property value was incorrect in the style system itself. r=rods

layout/html/document/src/html.css

@@ -1504,6 +1504,7 @@ select:-moz-dropdown-list {
 /* combobox dropdown list visible */
 select[-moz-dropdown-active]:-moz-dropdown-list {
   visibility: visible;
+  z-index: 2147483647;
 }
 
 :-moz-anonymous-block {

layout/style/html.css

@@ -1504,6 +1504,7 @@ select:-moz-dropdown-list {
 /* combobox dropdown list visible */
 select[-moz-dropdown-active]:-moz-dropdown-list {
   visibility: visible;
+  z-index: 2147483647;
 }
 
 :-moz-anonymous-block {