Index: src/wp-includes/css/editor.css
===================================================================
--- src/wp-includes/css/editor.css	(revision 30806)
+++ src/wp-includes/css/editor.css	(working copy)
@@ -166,7 +166,6 @@
 	box-sizing: border-box;
 	margin-bottom: 8px;
 	position: absolute;
-	opacity: 0;
 	-moz-user-select: none;
 	-webkit-user-select: none;
 	-ms-user-select: none;
@@ -183,18 +182,6 @@
 	margin-top: 8px;
 }
 
-div.mce-inline-toolbar-grp.mce-inline-toolbar-grp-active {
-	-webkit-transition:
-		top 0.1s ease-out,
-		left 0.1s ease-out,
-		opacity 0.1s ease-in-out;
-	transition:
-		top 0.1s ease-out,
-		left 0.1s ease-out,
-		opacity 0.1s ease-in-out;
-	opacity: 1;
-}
-
 div.mce-inline-toolbar-grp:before,
 div.mce-inline-toolbar-grp:after {
 	position: absolute;