Suddenly, this add-ons made self-updates and deleted all my favorite search engines! Besides, I can't even customize them anymore, I can't delete unwanted engines. I can't customize settings. FIX THIS PLEASE!
[RE] : I saved a BACKUP of my custom search engines as well! But as the settings are getting restored automatically, the option "Force reload of default search engines list" gets marked, then I loose my custom engines.
NOTE: All of this happened with the firefox 62 I made update just after this, thinking it was just a matter of compatibilty.
Anyway, looking forward to get good news soon!