Thanks to chrnno Rated 4 out of 5 stars

@chrnno: thank you very much for your review. Your suggestion worked perfectly.
Anyway, there's no need to uninstall Brief; simply close Firefox, delete all brief* sql files from the profile (or rename them) and restart Firefox.

This review is for a previous version of the add-on (1.6.2).  This user has a previous review of this add-on.