Rated 3 out of 5 stars

The extension works when the KeePassXC database is unlocked, but whenever Thunderbird refreshes an account and the database is locked, it will open a new browser page asking for OAuth2 confirmation for each account.

This review is for a previous version of the add-on (1.8). 

As the access tokens for oauth are stored in the KeePassXC database Thunderbird has no way to know these when the database is locked. This behaviour is intended and a security feature.