Index: src/wp-admin/plugin-editor.php
===================================================================
--- src/wp-admin/plugin-editor.php	(revision 61389)
+++ src/wp-admin/plugin-editor.php	(working copy)
@@ -285,6 +285,7 @@
 			$plugin_editable_files[] = $plugin_file;
 		}
 	}
+	sort( $plugin_editable_files );
 	?>
 	<ul role="tree" aria-labelledby="plugin-files-label">
 	<li role="treeitem" tabindex="-1" aria-expanded="true" aria-level="1" aria-posinset="1" aria-setsize="1">
Index: src/wp-admin/theme-editor.php
===================================================================
--- src/wp-admin/theme-editor.php	(revision 61389)
+++ src/wp-admin/theme-editor.php	(working copy)
@@ -106,6 +106,8 @@
 	$allowed_files = array( 'style.css' => $allowed_files['style.css'] ) + $allowed_files;
 }
 
+ksort( $allowed_files );
+
 if ( empty( $file ) ) {
 	$relative_file = 'style.css';
 	$file          = $allowed_files['style.css'];