Addon no longer needed as functionality to reorder attachments is now built in to Thunderbird 60.
TB 60, Method #1: In Compose window, use drag-and-drop on Attachments pane.
TB 60, Method #2: In Compose window, right click on Attachments pane, select "Reorder Attachments", use popup menu buttons.
For TB 52 and prior, OrderAtt was one of the most useful addons I've ever used. Most deserving congratulations to the addon author for creating something so indispensable the Thunderbird team saw fit to make it core functionality!
Many thanks for your feedback.
You are right, my extension is now fully integrated in TB. Great!
I don't know if I have something to do with that, but I'm happy to have helped the TB community somewhere!