changing style on dropdown list boxes to not allow selection. a=rickg r=cmanske

layout/html/document/src/html.css

@@ -1294,6 +1294,7 @@ sourcetext { /* XXX should not be in HTML namespace */
 
 /* combobox dropdown list */
 :-moz-dropdown-list {
+  user-select: none !important;
   background-color:inherit;
   border: 2px inset rgb(153, 153, 153);
 } 

layout/style/html.css

@@ -1294,6 +1294,7 @@ sourcetext { /* XXX should not be in HTML namespace */
 
 /* combobox dropdown list */
 :-moz-dropdown-list {
+  user-select: none !important;
   background-color:inherit;
   border: 2px inset rgb(153, 153, 153);
 }