I'm sorry, it will take some time to investigate.
If settings for other add-ons are gone too, it may be that Firefox profile data is broken. This my be not problem of this add-on.
Anyway, I will add buttons to import/export setting on version 2.15

If there is an error log at the bottom of the setting page on version 2.15.1, please report it.

thank you for your review.