It may be that thunderbird created a new profile during the update. try clicking help>troubleshootinginformation, scroll down to 'profiles and click 'about:profiles' and on next screen you can click to browse other profiles. look in imapmail folder for IMAP account or mail folder for POP account. if you see that info in an inactive profile, that may be the one you want. click the launch button to verify. if it works, and if your account logs in, that would indicate that thunderbird had retained the password. You can retrieve it at settings>privacy&security