re :I converted to Thunderbird 128,11.1esr in May 2025.

Please explain a bit more. Do you mean you were using 128.11.0esr and you upgraded to 128.11.1esr ? Or were you using a much older version ? If yes, it was older then what older version were you using?

Do you mean you did a complete new install (not upgrade) of Thunderbird 128.11.1esr? if new install - Where did you get it ? eg; from official website : https://www.thunderbird.net/en-US/thunderbird/all/ Or 'Windows App Store' or 'Snap' or Flatpak'

What Operating System OS are you using ?

You say "My address book did not migrate" That implies you tried to Copy and Paste your profile from one computer to another?

Did Thunderbird ask you to create a new mail account? If yes, then that tells me it could not locate the old profile, so where you got the install download from may shed some light on why this occured.

Dear Toad Hall, Thank you for your reply. via email. I'll answer your questions in order.

I was using V125 dot something. I received an email from Mozilla encouraging me to upgrade to the .esr version which I did. That's how I got to V128.11.1esr. There was a note in the email saying I could revert back to the former version but I don't have any way to do that. Getting to V128.11.1esr was an upgrade. My PC OS is Windows 11 Pro Version 10.8.26100, Build 26100. With respect to my Address Book, I did not copy and paste any profile, I just performed the upgrade: now I no longer have my address book. No, I did not not create a new mail account.

If additional info is needed please email again. Thank you for your help. I hope there's a fix for this situation..

Steve

re :I was using V125 dot something. That did not exist. Maybe 102* or 115*

The place to find that information is: In Thunderbird

• Settings > General
• Scroll down to 'Updates' section
• Click on 'Show update history'

Please find out what version you had before the current one. There has been much updating and changing to many files recently and it you used a much older one then it would tell me if a change occurred with the address books.

re :I received an email from Mozilla encouraging me to upgrade to the .esr version which I did. That's how I got to V128.11.1esr.

Well that's a bit weird because Mozilla doesn't send out emails. Thunderbird might prompt a pop up saying an update is available. You also would find it under 'Help' > 'About Thunderbird' where you may see a prompt to manually upgrade. Or you can look in the Updates' section (as previously mentioned) where there is a 'Check for updates' option.

Maybe you have installed an Anti-virus product which offers checking for program updates. Never allow any other software update program to check for Thunderbird updates because all to often they offer the wrong versions. Only let Thunderbird check for updates, but you can set it up to ask before actually upgrading rather than just do automatically.

re :There was a note in the email saying I could revert back to the former version

I find it very strange that they would even mention reverting back. It's not that simple to just simply revert back to an earlier version. The dedicated profile for installation was implemented many versions ago. https://support.mozilla.org/en-US/kb/dedicated-profile-thunderbird-installation You would need to start Thunderbird using a particular method using command line and '--allow-downgrade' instruction. or set Settings to always ask bfore up dating, then Exit Thunderbird and access profile and delete the 'compatibility.ini' file. Then uninstall Thunderbird before downloading the version you require which is from a different location

There is something very strange about 'getting an email from mozilla.' Please post an image showing the headers and content of that email.

re :No, I did not not create a new mail account

That tells me you should still be using the same profile and same mail account which also means same everything.

But as you use Windows OS.... Did you oiginally get Thunderbird from the 'Windows App Store' or did you get it from the official website: https://www.thunderbird.net/en-US/thunderbird/all/

This info is important because it tells me where your profile is located.

Can you look in the following locations and tell me what you find:

• C:/Users/user name/Appdata/Roaming/Thunderbird/Profiles/profile name folder
• C:\Users\username\AppData\Local\packages\MozillaThunderbird.MZLA_h5892qc0xkpca\LocalCache\Roaming\Thunderbird\Profiles\ profile name folder

Also check this: In Thunderbird

• Help > Troubleshooting Information
• Under 'Applications Basics' near the bottom look for 'Profiles' and click on the 'about:profiles'

It opens in a new tab Post an image showing everything.

Thanks again for your continued assistance.

I had Thunderbird Version 115.something

The only info in Update History is: Thunderbird 128.11.1esr (20250606210711);

                                                         Installed June 11, 2025 at 12:07:03 PM
                                                         Status: The update was successfully installed
                                                          There is no prompt to "Check for updates"

The info in Help>About Thunderbird is 128.11.1esr (32 bit) There is no prompt for an upgrade there but it does say "You are currently on the esr update channel." I think I recall responding to a popup from Thunderbird concerning taking advantage of 128.11.1esr.

I did use an application to manage updates but I now do all program updates myself or use the individual program's automatic update feature.

I originally got Thunderbird from the official website.

Info at C:/Users/user name/Appdata/Roaming/Thunderbird/Profiles/profile name folder shows

                      t6qyjzal.default and
                      wjq5g5o9.default-esr  
                    

The link to C:\Users\username\AppData\Local\packages\MozillaThunderbird.MZLA_h5892qc0xkpca\LocalCache\Roaming\Thunderbird\Profiles\ profile name folder could not be found. I tried making the back slashes into forward slashes to no avail.

.Help > Troubleshooting Information

Under 'Applications Basics' near the bottom look for 'Profiles' and click on the 'about:profiles' yields

Profile: default-esr Default Profile yes Root Directory C:\Users\mylocal\AppData\Roaming\Thunderbird\Profiles\wjq5g5o9.default-esr Local Directory C:\Users\mylocal\AppData\Local\Thunderbird\Profiles\wjq5g5o9.default-esr

and

Profile: default Default Profile no Root Directory C:\Users\mylocal\AppData\Roaming\Thunderbird\Profiles\t6qyjzal.default Local Directory C:\Users\mylocal\AppData\Local\Thunderbird\Profiles\t6qyjzal.default