If it helps, there is no "smart"anything in my profile:

find . -iname \*smart\*

<nothing>

Renaming "virtualFolders.dat" and "virtualFolders-1.dat" did not help either.

115 does not like something that came over from 102

See if you can fix it with this add-on:

https://support.mozilla.org/en-US/questions/1426387

Makes no difference. The Unified folders has to appear first.

open your profile folder by going to the Troubleshooting information on the help menu. and clicking the open button beside the profile entry. Close Thunderbird. Open the "mail" folder in file manager.

Locate the "smart mailboxes" folder

Now normally I would just say delete them. But just in case I can find someone that has a use for them in diagnosis.

Right click and select compress to zip file (I renamed the Zip smart.) Then delete the smart mailboxes folder

Restart Thunderbird.

This will force a complete rebuild of the unified folders

Does this make the folders appear and appear correctly?

Hi Matt,

Did you miss my previous post?

   "If it helps, there is no "smart"anything in my profile:
   find . -iname \*smart\*
   <nothing>

The "find" started in the root of my profile and did a case insensitive search of all sub folders and files for the fragment "smart".

There are no file(s) or folder(s) with the name fragment "smart" of any lower or upper case anywhere in my profile.

This folder was never created. Is that a clue?

Do you see a difference in what I told you to do and what you did?

I know it is truly astounding, but the contents of hidden files and folder are not found with these operating system tools and instead of doing what you were asked, which will show the folder you fell back to your previous erroneous attempt to locate something the operating system did not want to show you. https://serverfault.com/questions/139126/how-to-view-hidden-files-using-linux-find-command

I read over that server fault link. It was a bit weird. I have no trouble whatsoever finding hidden files on my system. For example, inside my profile:

# whoami

root

# pwd

/home/OurStuff/mozilla/Thunderbird/Profiles/Todd

# touch .TryAndFindMe

# chmod 400 .TryAndFindMe

# ls -al .TryAndFindMe

-r--------. 1 root root 0 Oct 8 22:39 .TryAndFindMe

# find . -iname .TryAndFindMe

./.TryAndFindMe

# find . -iname \*TryAndFindMe\*

./.TryAndFindMe

# find . -iname \*smart\*

<nothing>

I also checked my backup of my profile I made before upgrading fro 102 to 115. No "smart" anything over there either.

This is the "unified folders" I lost in 115:

Unified Folders https://yoyofumedia.com/one-unified-inbox-thunderbird/

The plot thickens !!!!

I created an additional, new profile and

    view->folders->unified

works perfectly.

https://ibb.co/CVyJQv2

Now to compare both's perfs.js to see what is screwing things up.

-T

p.s. note that the problem persists in safe mode too

I created a new, additional profile and the Unified Folders functions properly in the new profile.

I could not find anything wrong by comparing the new and old profile's prefs.js

mumble mumble

Note that the problem exists in safe mode too

Interesting, the new profile (bozo) did create "smart mailboxes":

$ find /home/OurStuff/mozilla/Thunderbird/Profiles/Bozo/ -iname \*smart\* /home/OurStuff/mozilla/Thunderbird/Profiles/Bozo/Mail/smart mailboxes

I copied the whole folder into my main profile. Made no difference.

More mumbling

Problem sure looks like: https://bugzilla.mozilla.org/show_bug.cgi?id=1853159

Problem sure looks like: https://bugzilla.mozilla.org/show_bug.cgi?id=1853159

That would mean https://bugzilla.mozilla.org/show_bug.cgi?id=1856997 is involved