Index: src/wp-includes/general-template.php
===================================================================
--- src/wp-includes/general-template.php	(revision 43600)
+++ src/wp-includes/general-template.php	(working copy)
@@ -3204,7 +3204,7 @@
 		'codemirror' => array(
 			'indentUnit'       => 4,
 			'indentWithTabs'   => true,
-			'inputStyle'       => 'contenteditable',
+			'inputStyle'       => 'textarea',
 			'lineNumbers'      => true,
 			'lineWrapping'     => true,
 			'styleActiveLine'  => true,