Might be https://bugzilla.mozilla.org/show_bug.cgi?id=1990571 Which Thunderbird version did you use before reinstalling Windows and which version are you running actually?

I am running version 144.0.1 (64 bit) now. I am not sure how to check the previous version number of Thunderbird, but seeing that was only a few weeks ago, I suspect it is the same 144.0.1 Also the new version has the previous profile from my backup. My Thunderbird is configured to automatic updates.

Update to v144 was available since October 14, 2025. Not sure whether you already used v144 when you reinstalled Windows on your PC. Try the following before we need to do more serious things: go to Help > Troubleshooting information and click "Clear startup cache" in the upper right box. You'll be prompted to restart Thunderbird.

If you are still missing your Local Folders I propose to downgrade Thunderbird temporarily to v143.0 You can download v143.0 from https://ftp.mozilla.org/pub/thunderbird/releases/143.0/ Before installing the older version open your actual version, go to Settings > General > Updates and activate the radio-button ◉ "Check for updates, but let me choose whether to install them" Then install v143 over v144. To launch v143 in your old profile you need to use the --allow-downgrade command: Hit the Windows key + R, type thunderbird.exe -p --allow-downgrade and hit Enter. This action will open the profile manager where you have to click "Start Thunderbird".

As a precaution: before doing anything create a backup copy of your "Thunderbird" folder (containing your profile) in ....\AppData\Roaming\Thunderbird\

Hi, thanks for your continuous help. The link you sent me got to this page? I am not sure that this is what you where aiming for? I have a copy of Thunderbird Setup V143.0.1,exe Is there a chance to see this in you-tube as I am not sure of all the steps involved Regards Ilio (ilio) Pieroni

The link you sent me got to this page? I am not sure that this is what you where aiming for? I have a copy of Thunderbird Setup V143.0.1,exe

yes this is the page where I sent you since I didn't know that you already have the installer for v143.0.1

Is there a chance to see this in you-tube as I am not sure of all the steps involved

I don't know of a YouTube video which would illustrate my instructions which IMHO are easy to follow: If you don't know what Windows + R key means have a look here https://tutorialtactic.com/blog/windows-r-is-used-for/ Windows + R keys open a Run window Copy the thunderbird.exe -p --allow-downgrade command line and paste it in the Run window, then hit OK.

Sorry, I can't join screen shots because I am a Mac user....

No I don't have trouble with windows+ R What I don't quite follow is when V143 is installed it will have a new profile folder I will need to replace it with my old one and hopefully it will import everything? If I am correct I can use the backup profile from yesterday ? If not can you please clarify what is going to happen after installing v 143. If it works out OK, the upgrade back to v 144 wont cause the Local Folder to disappear? Thanks Ilio Pieroni

The goal of our discussion is to allow you to start v143 in your actual profile because of bug 1990571 which came with v144 you cannot see your Local Folders. But if you try to launch a Thunderbird installation with a profile that was last used in a newer version, Thunderbird will refuse this and you'll get an error message https://support.mozilla.org/en-US/kb/dedicated-profile-thunderbird-installation#w_what-happens-to-my-profile-if-i-downgrade-to-a-previous-version-of-thunderbird

To circumvent this restriction I suggest you to start TB version 143 via the following "allow downgrade" workaround Windows + R keys open a Run window Copy the thunderbird.exe -p --allow-downgrade command line and paste it in the Run window, then hit OK This will allow you to open your actual profile with the lower 143 version. There is hope that your Local Folders will reappear in v143

What I don't quite follow is when V143 is installed it will have a new profile folder

I presume that your actual Thunderbird version is still 144.0.1, is that right? If you install version 143 don't launch it yet since in this case it will crate a new virgin profile. If you already have installed v143 launch it in your actual profile with downgrade option In described above.

Many people who have issues with 'Local Folders' not seeing folders have found it may be linked to pathnames being too long. So they renamed folders to a shorter length and it worked for them. It might be worth trying on any that have a longer name. Exit Thunderbird Access the Local Folders folder rename 'ACE MACHINE TOOLS' to eg: 'ACE M TOOLS' rename 'ACE MACHINE TOOLS.sbd' to eg: 'ACE M TOOLS.sbd' Delete 'ACE MACHINE TOOLS.msf' (when you restart - it should get recreated) or you could rename that as well 'ACE M TOOLS. msf'

Also any other thats longer such as 'Bread Machine Finder' and 'Chain Saw Sharpener' Could they be shortened to just 'Bread Machine' and 'Chain Saw '

It's up to you whether you want to see if that works.

REgarding going back a version: Mapenzi instructions are correct You can download v143.0 from https://ftp.mozilla.org/pub/thunderbird/releases/143.0/

• Select 'mac/'
• Select prefered language eg: en-GB is English British
• The click on the text link : Thunderbird 143.0.dmg

There is an an Alternative:

Setting > General Scroll to 'Updates' section Select 'Check for updates bt let me choose when to install them.' Uncheck 'Use a background service to install updates' - this will force the computer to ask if you really want to install update if you accidentally selected to update.

Exit Thunderbird Access profile name folder Delete this file: 'compatibility.ini'

Uninstall Thunderbird. Reinstall version 143.0.1

It should auto locate and use profile.

You did not post an image showing the contents of the 'Mail' folder, so I'm wondering if there are more than one Local Folders maybe one with a number etc.

So, it's worth checking is to see where your current 'Local Folders' is pointing to.

• Account Settings
• In left pane - select 'Local Folders'
• On the right locate 'Local directory:...'
• Click in the text area and use keyboard arrows to move to the far right.

• It should say:.../fws706fj.default-release/Mail/Local Folders

If it says something different click on the 'Browse' button It will open showing contents of current position, you can reselect the correct profile, Mail and Local Folders folder

I am quite confused, the image of the Profile Folder was taken on the 7th of this month. where it shows 2 folders starting with "fws706fj.... see image below. When I opened by backup to the 1ts of October the profile has changed to what it is now. And following Toad-Hall suggestion, see image below, the profile folders have changed name. When I opened by backup to the 1st of November it also shows the new profile name Different from the the 7th as stated above. If I don't here anything to the contrary I will follow Mapenzi recommendation the 9th of November. Thank you all for your contributions. Regards Ilio Pieroni