Rated 5 out of 5 stars

le Alan ar Feabh. 27, 2019 · buan-nasc

There are numerous comments that the extension doesn't work with the latest version of Thunderbird. However, this fixes it:

Go to Thunderbird>>Tools>>Options>>Advanced>>General>>Config Editor

Scroll down to extensions.tbsortfolders@xulforum.org.accounts

Right-click and select Reset

Repeat for extensions.tbsortfolders@xulforum.org.defaultaccount

Restart Thunderbird

Acknowledgements to arikurumo for finding this