More information about my problem. I was mistaken about when I upgraded to V78. It seems I previously upgraded to V78.7.1 back in February and all was running just fine. On March 3, Thunderbird installed V72.8.0, and that is when everything quit working. It lost my login credentials, my mail boxes, my folders, all of it lost all of my folders, logins, and configurations. After the update, it began the "new system" setup, asking for my email servers, etc.

I have tried to restore my old configuration by editing the profile file, to no avail. I tried to point it toward my local folders directory, but it is treating each file in there as a folder. It does not reconstruct the nested mailbox files, even though the matching .TOC files are there.

Is there some configuration command I need to make to have it understand the old Folders format?

I have discovered that the 'gcontactsync" add-on doesn't work with the latest version of Thunderbird. I have been using that for years and I didn't uninstall it when Thunderbird upgraded from 78.71. to 78.8.0. Could that be part of what caused my problems?

You have two possible causes. Which it is is a guess.

Goto the troubleshooting information on the help menu and click on the about:profiles entry in the basic information part of troubleshooting information.

Do you have more than one profile registered there? if so use the launch profile button to have a look and see if that profile is your old one. In may have just switched profiles on you.

Could how many profiles you have listed. Then from the troubleshooting information click the show button for the local profile folder. once the windows file manager opens click the up arrow. Does the number of folders shown match the number in the about profiles? (might be one has been "lost" completely.

The second is a more problematic one involving corruption. While much of the information in this article is out of date the information about the prefs.js is as current as today. http://kb.mozillazine.org/Recovering_a_profile_that_suddenly_disappeared#Corrupt_or_empty_prefs.js

It has taken me 2 days to get it working again, but I seem to have mostly gotten my Email working again. For some reason, when I upgraded, it decided that all of my configureation was lost. This may have been because I hold all of my folders on a separate disk drive from my system drive, and it seems that the update could not find them? Not sure if that was it or something else. I found several instances of Thunderbird profiles in several different directories. Many of them left over from previous upgrades.

I was finally able to get the profiles edited and working to handle both of my mail services. To find all my folders, I had to find the one that Thunderbird created when I installed it, delete that one, and rename the old one to the name Thunderbird used (Local Folders-1).

That go me my local folders back.  I was not able to find a way to configure where Thunderbird stores folders.  

I still have found several Profile directories on my system, but I hesitate to go back and delete them for fear of breaking it again. I have found Thunderbird Profiles in my C:\Users and on myt data drive D:\Users. I suspect that having most of my user data on a separate disc drive from my system files, is what caused the initial problem.

I still havn't found the way to load my Google Contacts file into Thunderbird, now that "gcontactsync" is no longer working.

Greg

I am not sure where your data is stored, but it is clearly not appropriate or there is another fundamental problem. Local folders being stored in local folders-1 is proof something is not right. The numerical suffixes only appear when their are issues accessing file. You profile should contain not files that have those suffixes.

So it he "other drive not on the local machine? or subject to accessibility issues caused by networking, synchronization or backup?

Matt, The other drive is fully mounted disc on my PC. I run a multi disc system. My C: drive is on an SSD. I use that to speed-up loading, etc. It contains all of the system and program files. All my data (My Documents) are on a standard IDE D: drive, which is always mounted and spinning.

I did try the trouble shooting section and found two profiles. I tried both of them, but neither included my old installation and folders.

Is there any documentation outlining the what files/directories Thunderbird uses, and where it expects to find them (location and name)?

Is there any way I can rename the my local files directory to remove the -1, and then tell Thunderbird to use the modified name? If I need to, I could do a clean install of Thunderbird and them move all of my old folders into the fresh install. But since it seems to have access to them now, I am hesitant to continue messing with it.

Greg

Thunderbird stores nothing in "My Documents" or "Documents" and in fact will refuse to use it as an unsafe location. (that dates back to V24. https://support.mozilla.org/en-US/kb/dangerous-directories-Thunderbird-account-settings)

Thunderbird expects to find the profiles.ini file which points to the profile in %appdata%\Thunderbird. you can type that into the windows file manager to have it displayed. The %appdata% is a location defined by windows not an absolute path. See https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data