Try:
sudo apparmor_parser -R usr.bin.thunderbird
If it doesn't work, replace "usr.bin.thunderbird" with the output of this command:
ls /etc/apparmor.d | grep thunderbird
Try:
sudo apparmor_parser -R usr.bin.thunderbird
If it doesn't work, replace "usr.bin. thunderbird" with the output of this command:
ls /etc/apparmor.d | grep thunderbird