Restore previous pages

[tnffuser]

How do I stop the "Sorry. We’re having trouble getting your pages back" notice from popping up each time I open FF.
I usually use the "X" to exit each session, does this exit differently than using the menu "Exit"?
Restore previous session IS unchecked in General/Startup, checking and restarting, then unchecking and restarting did not stop the notice.
Where else is this controlled?

[dickvl]

Does this still happen if you use the Exit/Quit menu item?

If you use the close X then Firefox will first try to close the window and if there are no other windows left then try to close Firefox. If you use Exit then a shutdown is immediately initiated. Using Exit is the preferred way, especially if you encounter issues when using the close X.