Beginning with version 102, the default order is threaded. Here are steps to change default to unthreaded:

You need to highlight each folder and click View>sort by>unthreaded. If this applies to just a few folders, just repeat the process as necessary. If you have many folders or plan to add many new folders, you may wish a different approach, below:

More info: To change default for new folders, In config editor, you can change default that applies to NEW folders you set up: mailnews.default_view_flags 0=unthreaded

Config editor is available at Tools>settings>general and scroll to bottom right.

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To set many *existing* folders, follow these steps: (I creates a crude video that walks through the steps at

   https://davidkirk.org/SettingDefaultFolderView.mp4  that demonstrates the following steps:

  First, highlight a folder that you have set to unthreaded
  In the Message List view, in the column header, on the far right, open the options button that shows    
   context menu. (See attached screenshot):
  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.

Two of my pet peeves with technology are:

(1) Something changes out of the blue to something inferior.

(2) The way to change some behaviour you don't like - which should be available via a simple flip of a switch - just can't be found or is only found with great difficulty.

These are often encountered separately but are worse when encountered together.

I have thousands of folders and sub-folders in Thunderbird and, all of a sudden a few months back, I am now faced with doing the below when I go into view the emails in them:

View + Sort By + Unthreaded

I keep searching for that simple toggle switch which surely must exist but doesn't.

Why did the Thunderbird people inflict this on me? I've been using Thunderbird forever and, while there might be the rare time I actually want threaded viewing, 99 times out of 100, I don't.

Your displeasure is shared by many, and I am one of those, as well. I have seen no explanation on this. Fortunately, the solution I posted works and takes just a few minutes. For the future, I suggest remembering that config setting and do it immediately after an install and before setting up accounts.

Thanks David. I tried this method and, in my case, the uppermost level under which all my folders belong is what is known as my email account (which is my email address) so when I "applied current view to ....." that "Folder and it's children", it asked the below and I clicked on OK:

Apply the current folder’s view to xxxx@xxxxxxxxx.com and its children?

It didn't then pause or anything for any amount of time but, unfortunately, checking out random folders, it hadn't changed them over to the unthreaded view. And, yes, my Inbox view is set to unthreaded.

Kind of a segway but I find it interesting that you have gmail running under thunderbird as that would be something I would be interested in as well so will be looking into that.

Hi David. I posted a reply to what you said last but aren't seeing the reply I posted.

Hi David. I tried what you said but it didn't work with me. My upper most "folder" is the my thunderbird account which had my email address xxxx@xxxxxxxxxx.com and I applied the current view of my INBOX to same but any folders that I haven't recently changed are still using threaded sorting.

That's strange. I posted another response what with the first one not showing and it isn't showing either.

That's strange. I posted another response what with the first one not showing and it isn't showing either.

We have had to implement a feature that flags replies as possible spam or needing moderation (hides them) due to links and emails being posted and for the replies to be seen by public they need to be approved.