Review for ThunderThings by KomIvV
Rated 1 out of 5 stars
The app does not work
So if you would like it to work, could you please provide more info about what you are encountering, what version of Thunderbird you are using, etc?
Also, did you install the macOS app that is required to communicate between the add on and Things? Information at https://github.com/snchong/thunderthings (which is linked to from the add on page).
To create your own collections, you must have a Mozilla Add-ons account.