Index: wp-includes/css/media-views.css
===================================================================
--- wp-includes/css/media-views.css	(revision 22985)
+++ wp-includes/css/media-views.css	(working copy)
@@ -65,6 +65,10 @@
 	-webkit-appearance: textfield;
 }
 
+.media-frame :-moz-placeholder {
+   color: #a9a9a9;
+}
+
 /* Enable draggable on IE10 touch events until it's rolled into jQuery UI core */
 .ui-sortable,
 .ui-draggable {
Index: wp-admin/css/wp-admin.css
===================================================================
--- wp-admin/css/wp-admin.css	(revision 22985)
+++ wp-admin/css/wp-admin.css	(working copy)
@@ -750,6 +750,10 @@
 	background-color: #eee;
 }
 
+:-moz-placeholder {
+   color: #a9a9a9;
+}
+
 /*------------------------------------------------------------------------------
   1.0 - Text Styles
 ------------------------------------------------------------------------------*/