Commenting out the line that reads
export MOZ_ENABLE_WAYLAND=1
in /usr/lib/thunderbird/thunderbird.sh makes the problem go away, because the application will now run as an XWayland client.
Commenting out the line that reads
export MOZ_ENABLE_ WAYLAND= 1
in /usr/lib/ thunderbird/ thunderbird. sh makes the problem go away, because the application will now run as an XWayland client.