Maybe there is a relation to a possible Bug:
Thunderbird also forgets all open Tabs (Calendar and Tasks with Lightning) and the properties (Position of Cols like Priority or Date of Appointments/Tasks)
Also it forgets these Cols in the SideWindow of Lightning in the Mail Tab
Maybe there is a relation to a possible Bug:
Thunderbird also forgets all open Tabs (Calendar and Tasks with Lightning) and the properties (Position of Cols like Priority or Date of Appointments/Tasks)
Also it forgets these Cols in the SideWindow of Lightning in the Mail Tab