AttachSure by Naveen

AttachSure helps prevent accidentally sending Gmail messages without an attachment.
When you try to send an email with no attachment, the extension displays a confirmation prompt before the message is sent. You can either cancel and add the attachment, or choose to send the email without an attachment.
Messages that already contain attachments are sent normally without interruption.
The extension works on Gmail in Firefox and does not collect, store, or transmit personal data.