Do not use for-in loop to iterate over array.

Author: Reinmar

plugins/filebrowser/plugin.js

@@ -359,7 +359,7 @@
 		var definition = evt.data.definition,
 			element;
 		// Associate filebrowser to elements with 'filebrowser' attribute.
-		for ( var i in definition.contents ) {
+		for ( var i = 0; i < definition.contents.length; ++i ) {
 			if ( ( element = definition.contents[ i ] ) ) {
 				attachFileBrowser( evt.editor, evt.data.name, definition, element.elements );
 				if ( element.hidden && element.filebrowser ) {