--- a/mail/components/compose/content/MsgComposeCommands.js
+++ b/mail/components/compose/content/MsgComposeCommands.js
@@ -4336,17 +4336,16 @@ function RenameSelectedAttachment()
 function AttachmentElementHasItems()
 {
   var element = document.getElementById("attachmentBucket");
   return element ? (element.getRowCount() > 0) : false;
 }
 
 function OpenSelectedAttachment()
 {
-  let child;
   let bucket = document.getElementById("attachmentBucket");
   if (bucket.selectedItems.length == 1)
   {
     let attachmentUrl = bucket.getSelectedItem(0).attachment.url;
 
     let messagePrefix = /^mailbox-message:|^imap-message:|^news-message:/i;
     if (messagePrefix.test(attachmentUrl))
     {