but
5. If Thunderbird is closed while still OFFLINE, then a re-launch of Thunderbird in any state will reveal
     that all mailboxes and all mail have been deleted.

06 May 2026 USA Just to inform users: All mailboxes and all mail in profile are catastrophically and irretrievably deleted when I: 1. Change the location of the profile folder. 2. Make appropriate change in profiles.ini reflecting the location change. 3. Launch Thunderbird in Offline Mode (launching in OFFLINE mode is the fatal event). 4. Mailboxes will appear during this one launched session but 5. If Thunderbird is closed while still OFFLINE, then a re-launch of Thunderbird in any state will reveal that all mailboxes and all mail have been deleted. All mailboxes, and of course, all mail in the profile are catastrophically and irretrievably deleted. I was lucky that I made a backup before changing profile location. The deletion of mail and mailboxes occur at the close of Thunderbird's OFFLINE state. An examination of the profile folder indicates the destruction has occurred upon closing of Thunderbird in OFFLINE state. It is not the re-launch of Thunderbird that causes the catastrophic deletion. The deletion occurred when Thunderbird was closed in its OFFLINE state. To successfully change the profile location I must: 1. Make the change to profile location. 2. Make the appropriate change to profiles.ini 3. BE SURE to make the FIRST LAUNCH of Thunderbird in ONLINE mode--ONLINE only. 4. Once 1,2,3 are done, then Thunderbird does not corrupt the profile folder. Conditions that MIGHT make my configuration uniquely affected: 1. I use Proton Mail Bridge in conjunction with Thunderbird. 2. My Profile folder is on a network share that is letter-mapped in Windows. 3. I have about 10 email addresses in Thunderbird that are Outlook IMAP, Gmail IMAP, and of course, Proton Mail. I've been using Thunderbird a couple of years in this configuration with no problems. I just decided to rename my profile. So, this is my first discovery of the problem.