After I reinstalled Windows and reinstalled Thunderbird, task reminders no longer work. I create tasks using the New Task button on the Tasks tab with a due date and time in the New Tasks dialog. This used to result in a Reminders window popping up at the scheduled date and time. Now, however, nothing happens. As far as I can tell, all the settings on the new install of Thunderbird are the same as I had before. The screenshot shows what I used to get, and what I would like to get again.

Is some setting required to get a Reminders window?