Don't worry about your calendar data, it is left untouched and will be available again if you follow these steps to restore Lightning: This may happen if the update of the add-on is stuck. Lightning disappears after a Thunderbird update (release and beta versions)
4 After a Thunderbird update, the first day of the week in the calendar views is set to Sunday.3 Lightning reappears after a Thunderbird update although I opted out (release and beta versions).2 I am on Linux and Lightning disappeared after Thunderbird got updated (release and beta channel).1 Lightning disappears after a Thunderbird update (release and beta versions).
