Rated 2 out of 5 stars

le Firefox user 110ea8 ar Meith. 1, 2023 · buan-nasc

Unreliable. Once the Dropbox-connection is added, any upload works only once. All consecutive uploads quit with the error msg:
Upload Error - Unable to upload file xyz to Box.

You either have to restart Thunderbird or re-inititate the connection (i.e. delete the old one and add a new connection).