Index: wp-includes/css/admin-bar-rtl.css
===================================================================
--- wp-includes/css/admin-bar-rtl.css	(revision 29689)
+++ wp-includes/css/admin-bar-rtl.css	(working copy)
@@ -16,6 +16,7 @@
 	-webkit-transition: none;
 	transition: none;
 	-webkit-font-smoothing: subpixel-antialiased; /* Prevent Safari from switching to standard antialiasing on hover */
+	-moz-osx-font-smoothing: auto; /* Prevent Firefox from displaying thin font when themes turn on font-smoothing */
 }
 
 .rtl #wpadminbar * {
Index: wp-includes/css/admin-bar.css
===================================================================
--- wp-includes/css/admin-bar.css	(revision 29689)
+++ wp-includes/css/admin-bar.css	(working copy)
@@ -16,6 +16,7 @@
 	-webkit-transition: none;
 	transition: none;
 	-webkit-font-smoothing: subpixel-antialiased; /* Prevent Safari from switching to standard antialiasing on hover */
+	-moz-osx-font-smoothing: auto; /* Prevent Firefox from displaying thin font when themes turn on font-smoothing */
 }
 
 .rtl #wpadminbar * {