Now as Self-Destructing Cookies is gone with FF57+, this is a valid replacement. Looking forward to local storage support with FF 58.

Just one thing I do not like: the json export/import format is too complicated, making it nearly impossible to manually craft lists (like I did for migrating from Self-Destructing Cookies).
Please consider switching back to the V1 format or something similar, then I'll give five stars ;-)