It seems as the interface thinks the window containing Thunderbird is longer than it actually is. The bottom part of the interface is missing and there's no scroll bar. This is most apparent to me in the Address book, where part of the fields is invisible, as are the Cancel/Save buttons. When I start Thunderbird, that bottom part of the interface would appear for about a second and then disappear. Resizing the window doesn't help. When I start Thunderbird in Troubleshooting mode, the interface works fine, but "Reset toolbars and controls" and "Disable all add-ons" doesn't fixt the issue. It might have started when I connected a secondary monitor, positioned above the primary. I thought disconnecting that monitor fixed it, but I since reconnected it and the issue now won't go away except when in Troubleshoot Mode.