I have over 200GB of emails under my profile folder. Been using TB for a long time. Tried to upgrade to 91.x.x from 78.14.0 from within Thunderbird. (I tried uninstall 78.x.x and install 91.x.x fresh as well and tried both 32-bit and 64-bit versions) Windows 10 After the upgrade, and I launch 91.x.x, TB UI does not show up and there are several processes running. I thought it is trying to perform some conversion and left the machine on for 6 hours, but still not showing up. When I uninstall 91.x.x and install 78.x.x back, I am able to see all of mails again (I need to use -- allow-downgrade option) I also tried to delete all .msf files, but still the same issue with 91.x.x.. I also tried to launch Thunderbird in safe mode, and still the same issue. Any idea what I need to do to upgrade to 91.x.x?