Developer reply by Itagaki Fumihiko
Rated 5 out of 5 stars
Great addon, sad it doesn't work for new versions, BUT IS NOT NECESSARY ANYMORE. You can sort the folders by going to Settings -> Account Settings and dragging the accounts from the left panel.
It is not the reordering of folders, but the reordering of accounts. It has been possible since Thunderbird 91. However, the ability to sort folders is not yet available. It is currently under development.
To create your own collections, you must have a Mozilla Add-ons account.