I was thinking about this over the last few days and I think there is an opportunity to really improve the Attachment UX in Thunderbird Mobile. I attached pictures of each step and then a gif showing the UX in action.
My thought is that the message header will have an attachment icon, and if you tap the attachment icon a tray that slides in from the right (similar to the accounts tray that slides from the left) will contain the message attachments. I think this could be a really great user experience.
I hope everyone likes it.