As I've understood the new feature is no longer to sort folders alphabetically. New folders/subfolder will be located at the end the folder list. So you'll have to sort them manually now. But I miss a View menu item Folders > Sort by alphabetical order... unless there in a new hidden setting ??

Yes, I got that already, thanks. The issue is that my folders were already sorted, and they got messed up with the installation of the latest version.

FYI It's a legit bug https://bugzilla.mozilla.org/show_bug.cgi?id=1973085 not yet fixed in 140.

That bug might be related, but it's not what I am getting at. The situation is that once I have reordered the folders, they should not be messed up again. I opened Thunderbird, to find that a bunch of folders starting with A for instance, were underneath the M's, but not all of them. The same issue happened elsewhere, too. As it is, I have manually reordered them, in the hope they don't get mixed up again. I rather wish they were automatically alphabetized like before.

It still may be related, perhaps even highly. So the next step is evaluate in 2-3 weeks when it's on 140. Or sooner if you want to try beta.

Okay, I'll wait and see what happens.

Me too. Order of folders in left folder pane messed up. Tbird briefly has a function of manually re-ordering folders - yay, finally! - but now it seems to be gone again. Please bring this function back!

I am on 141.0 now, and it seems to be okay. I added a test folder, to see if it showed up alphabetically, and it did. And they are all still in order.

As harmonk pointed out, you can't resort them manually anymore. Is it a matter of not being able to implement automatic alphabetical and manual sorting in the same release? I can't imagine needing to do it manually at this point, but perhaps harmonk has a use case for it.