Somehow Thunderbird got corrupted when the disk got full. Now one of my GMail IMAP accounts is stuck on 'Checking mail server capabilities...'. Nothing else works. No mail gets downloaded anymore. Initially, after the disk full, I've restarted Thunderbird and saw inside the left-hand panel about 30 duplicates of one of my IMAP accounts. The duplicate accounts were gone after restarting the app. I've already tried disabling the problematic IMAP server (setting a wrong URL for server address) but it doesn't work, none of the other accounts download anything.