You also need View>sort by>unthreaded. More info: In config editor, you can change default that applies to NEW folders you set up: mailnews.default_view_flags 0=unthreaded

To set many folders, follow these steps:

   In the header view, in the column header on the far right, open the options menu.
   At the very bottom is the option:
   -> "Apply current view to..."
   -> "Folder and its children..."
   -> Hover over an account
   -> In the next menu don't select a folder. Instead select the account name itself.

This isn't a perfect solution, but it does address the issue of unthreading many folders.

This used to not happen, someone imposed it on us and I DO NOT WANT THREADING! It is stealing so much of my time today and i have NEVER CHOSEN THREADING and DO NOT WANT IT!!! I am not into all this complicated techie stuff that sometimes works and sometimes does not.

Make it a choice BUT DO NOT FORCE IT ON US!!!! PLEASE!!!! TURN IT OFF!

I agree: It should be much easier to turn it off, or not make it the default. However, the processes above do turn it off.

TB is not honoring the default settings. I have changed mailnews.default_view_flags to 0 and set the View -> Sort by to unthreaded and this morning, all on its own Thunderbird decided to change the sort by to threaded.

The setting in config editor only applies to new folders you set up. For existing folders, you need to follow the above steps.