A number of possibilities.

1. https://thunderbirdtweaks.blogspot.com/2019/09/i-lost-my-profilemail-on-update-to.html
2. http://kb.mozillazine.org/Recovering_a_profile_that_suddenly_disappeared and http://kb.mozillazine.org/Recovering_a_missing_profile
3. A Corrupt prefs.js file, replacing it with a backup is the best solution, otherwise you messing with recovering profile data as discussed in 2. above.

I seem to have 29 prefs.js files.

It could be corrupted as pref.js is just 15kb. prefs-27.js is 112kb as are earlier versions. prefs-28.js is alsio 15kb

Could I just copy prefs-27.js to prefs.js?

Thanks

Is you profile stored on a NAS or other non fixed hard disk, or synchronized to the cloud using one of the file syncing services like onedrive.

My profile It is stored on a Samsung Evo SSD in the laptop I am using. I also have backups on an external drive.

I renamed prefs-25.js to prefs.js and it does work now. Folder and accounts are all back now.

Quite a few emails are now in different folders. I am not sure why.

Seems solved.

Thanks

I asked because you should not have prefs(XX).js files. There should only be one prefs.js and the existence of others would indicate that while you appear to have solved the immediate problem you still have whatever is causing these multiple files to appear.

As you only have the local drive in play, I would guess the problem is either backup or anti virus related. These files are created when Thunderbird attempts to access the prefs.js file and can not. Th two most common causes of this type of contention (outside of remote drives and cloud sync) is anti virus scanning. We recommend you exclude the Thunderbird profile from and anti virus scanning. The other is streaming backups which start backing up a file as soon as it is changed, resulting in the file not being available for a subsequent change while the backup occurs.

But I encourage you to determine what is causing the contention issues that create these files and take action to stop whatever it is interfering with Thunderbird's function. Further/Future problems can almost be guaranteed at this point.

Thanks. Do you what the files for the cache2 directory are for? Mine is now occupies 1GB. Can they be deleted without deleting mails or anything else?

There is nothing in the appdata\local folder that is required to run Thunderbird. The profile is stored in appdata\roaming and is the entirety of what is needed to move Thunderbird's profile to another computer.

Having said that the size of the cache is set in the application at options > Network & Disk space. You can also clear the cache at that location with a button press.

Sorry, I meant the cache 2 directory in profiles

\Thunderbird\Profiles\d711fnwp.default\cache2

where there are 3 sub-directories

doomed entries index

This is a 1GB folder.

Thanks

Sorry, I meant the cache 2 directory in profiles \Thunderbird\Profiles\d711fnwp.default\cache2 where there are 3 sub-directories doomed entries index This is a 1GB folder. Thanks

So did I. Thunderbird stores data in two locations.

C:\Users\[user name]\AppData\Roaming\Thunderbird\Profiles

and

C:\Users\[user name]\AppData\Local\Thunderbird\Profiles

The cache (in local) should not be in the same location as the primary profile which contains the prefs.js file (roaming).

My C drive has Windows 10 installed. The paths mentioned both exist on my C: drive but not ever accessed since 2017, as I changed the default location when I installed the SSD.

My live profile is stored on a D:\ partition on the same drive (where I store my actual data).

I have my profile in

D:\Username\Thunderbird\Profiles\d711fnwp.default

Then there is a D:\Username\Thunderbird\Profiles\d711fnwp.default\cache2

cache2 is 1GB in size

Is this needed?

as I said, use the inbuilt tools to empty the cache which I assume included the cache2 folder. If not just delete it with Thunderbird not running. If it needs it it will recreate it.

Thunderbird updated and then all of the folders are missing. Mail is continuing to download so the accounts are there somewhere. The address book is empty too.

When I click on About Thunderbird, the popup screen says that "You are currently on the release update channel"... AND "applying update".

I left it all night to see if the update would complete but it did not.

I am afraid to try to download and reinstall Thunderbird as it would likely overwrite all my settings and I will lose all my emails and my address book.

I have a back up but it is a few months dated, so the interim emails will be lost, so I would prefer to try to make this copy work.

Can you start Thunderbird with - p command line (search on start run, select that run app, on the small field enter thunderbird -p and press enter keyboard) and mention us how many profiles do you see there? If there are multiple choices then remember which one was selected, stop your internet connection (mandatory) and select each one and see if can see your old emails on any of them.