After upgrade to 20.10 Thunderbird stops with parsing error

I was experiencing the same problem just earlier after installing an official language pack by Mozilla. After closing and restarting Thunderbird, I was shown a popup with the exact same message you posted, and couldn't get Thunderbird running again.

Based on messages in this (German language) forum thread: https://www.thunderbird-mail.de/forum/thread/85658-thunderbird-startet-nicht-bzw-gibt-fehlermeldung-nur-im-safemode-m%C3%B6glich/?postID=468615, others are having the same problem, also after having recently installed or updated language packs.

I managed to solve the problem on my end by moving the offending file ([email protected], in my case) out of Thunderbird's extensions directory. On my system, all my Thunderbird settings, including the exensions directory, reside at /home/MYUSER/.thunderbird/RANDOMSTRING.default.