Ubuntu 18.04 Thunderbird 102.4.2 Just happened today, everything was working yesterday after update and upgrade (which I believe did not include Thunderbird). Left and right windows are blank. Can send emails, receive email arrival notifications, and view address books and filters, but cannot view folders, folder contents, and messages. Have rebooted, reloaded Thunderbird, tried moving a profile from another computer with no success. Have also noted that calendar tab does not appear. Tried troubleshooting with extensions disabled. What might I have missed? Thanks, in advance, for any help.