Going to 91 first is recommended, as Thunderbird does it upgrade adjustments at new versions. Then, upgrade to 102. Do full backup with Thunderbird not running prior to each step. Very important. Some antivirus programs interfere, so if you use one, check that it has ability to leave Thunderbird alone. Going back to prior version is always problematic, so I advise, even if you experience difficulties, to stay the course until issue rectified. Be sure to do the backups.

David, thanks for replying. Your reply creates a few additional questions:

• By backup, are you talking about a backup of the files on my hard drive, or does Thunderbird have its own backup of just its files?
• In either case, how do I restore the backup if something catastrophic occurs? This is especially pertinent if you're talking about a generic backup program like Norton Backup. I run Norton Backup monthly, but I would have no way of knowing what folders to restore to rebuild my Thunderbird email folders. On the other hand, if Thunderbird has its own backup/restore, is that something that's invoked from within Thunderbird?
• You mentioned that some antivirus programs might interfere with Thunderbird.Were you referring to the antivirus program possibly interfering with the Thunderbird upgrade process? If so, I could simply turn off the antivirus and firewall parts of my antivirus program (Norton 360). Or were you talking about an antivirus program scanning emails for viruses and spam?

Thanks in advance for any and all responses.

I'll try to answer what I can. Thunderbird does have a backup feature, but only with ver 102, and only for profiles smaller than 2 gig. I have seen problems on the forum with attempted restores from commercial backup products, such as Norton and others. The problem, as I see it, is that automated products may do their backups while Thunderbird is running and that will always produce a corrupted backup. The only safe backup is one done when Thunderbird is not running. This is because Thunderbird does not release the files and backup software misses them. So, if you use a commercial backup product, use it when THunderbird is not running to be safe. The profile itself will be at c:\users|<yourID>\appdata\roaming\thunderbird. If you backup that folder, (again, when Thunderbird is NOT running), you will have a reliable backup. Restoring is simply copying it back to the same place.

I am no guru on antivirus issues, but the great majority of problems during upgrades are because some antivirus programs interfere with the update, causing a corrupted update. Some antivirus software have the facility to ignore email software. If possible, disabling antivirus is preferred during upgrade.