Index: src/wp-includes/css/buttons.css
===================================================================
--- src/wp-includes/css/buttons.css	(revision 43344)
+++ src/wp-includes/css/buttons.css	(working copy)
@@ -59,14 +59,12 @@
 	box-sizing: border-box;
 }
 
-/* Remove the dotted border on :focus and the extra padding in Firefox */
+/* Remove the dotted border on :focus in Firefox */
 .wp-core-ui button::-moz-focus-inner,
 .wp-core-ui input[type="reset"]::-moz-focus-inner,
 .wp-core-ui input[type="button"]::-moz-focus-inner,
 .wp-core-ui input[type="submit"]::-moz-focus-inner {
-	border-width: 0;
-	border-style: none;
-	padding: 0;
+	border: 0;
 }
 
 .wp-core-ui .button.button-large,
Index: src/wp-includes/css/editor.css
===================================================================
--- src/wp-includes/css/editor.css	(revision 43344)
+++ src/wp-includes/css/editor.css	(working copy)
@@ -670,11 +670,9 @@
 	box-shadow: 0 1px 0 #cccccc;
 }
 
-/* Remove the dotted border on :focus and the extra padding in Firefox */
+/* Remove the dotted border on :focus in Firefox */
 .mce-window .mce-btn::-moz-focus-inner {
-	border-width: 0;
-	border-style: none;
-	padding: 0;
+	border: 0;
 }
 
 .mce-window .mce-btn:hover,