Hello,
Firefox 66 is now migrating add-ons data to a new storage and there can be cases when you loose you data:
https://www.ghacks.net/2019/02/16/firefox-extensions-to-use-different-storage-type-in-firefox-66/

If this is the case, go to dials page / click the upper right corner menu and select "History / backups" - these backups are stored in a different storage and should not be affected by the migration.

If this doesn't help, please contact me to my support e-mail.

Also note that downgrading Firefox will also clear your addons data (https://www.ghacks.net/2018/08/06/dont-downgrade-firefox-63/)

Best regards,
Juraj Mäsiar