Hi,
I downgraded one of my systems to Thunderbird 78, and have put in a
dnf
exclusion for upgrades of this application for the time being. That one
is working ok, and I was able to recover the addressbook there. Will
wait for the next Fedora-distro update to Thunderbird on the other
system to see if anything changes.
just a suggestion: Couldn't you export your addressbook as vcf on 78 and
import it after upgrade on 91?
Best Regards
Bjoern