More information about just how broken things are:

When reinstalling I've tried unselecting the "Mozilla Maintenance Service" as well as the various shortcuts for the app, but the bloody service and desktop shortcut are still installed/created.

Okay Mozilla, you're being really skeevy here. I deselect bloody maintenance service, it still gets installed. I replace maintenanceservice.exe and maintenanceservice_installer.exe with 0 byte read only files immediately after installing, and you STILL manage to install the service and upgrade from 128SR3 to the non-functional 131 which admonishes me for not staying on the mainline branch... WTF?

I finally got v128 to stick (for now), but it was far more involved than should be required!

Install 128 w/o maintenance service. Wait for the damned service to appear anyways when closing the installer. Uninstall the maintenance service from Windows Programs & Features. Replace place dummy maintenanceservice files in the Thunderbird folder as above. Open the v128 installer in an archive application like Peazip, extract everything but the bloody maintenance files into a temporary folder. Replace the files in C:\Program Files\Mozilla Thunderbird with those from the archive to "downgrade" back to the version you actually thought you were installing.

You omitted some information. Was this a fresh install? Is a Windows setup? If not a fresh install, what version were you using?

You omitted some information. Was this a fresh install? Is a Windows setup? If not a fresh install, what version were you using?

Did I? I don't believe I did really.

"Is it a Windows install?" The path "C:\Program Files\Mozilla Thunderbird" and reference to "Windows Programs & Features" would indicate yes.

"Is it a fresh install" No, as indicated, my existing installation suddenly started telling me I was on a monthly release.

"What version were you using" Okay, yes, this I did not say, but I do not know... the "maintenance" service clobbered it. Presumably 128 since I was, as far as I know, up too date. And reinstalling 128 kept "upgrading" to 131.

If your current installation said you were on a monthly release, my guess is you were on 130.0, another unsupported release that may not have had the same warning message. Regardless, that version you were using did not come from thunderbird.net or from an upgrade from the official release. I encourage you to go to setings>general and stop autoupdate until the next official release is announced and then select it.

Well... I'm having exactly the same problem. Somehow my Thuderbird V 128.3Oesr managed to update itelf to V131.0 despite the fact that autoupdate was switched off. I've been trying for 2 days to revert back, but when I reinstall V 128.3Oesr it is definitely that version until I apply my profile. When I apply my profile Thunderbird just switches to V131.0 instantly and nothing further has been installed as far as I can tell. The problem is that my extensions don't work in V131.0 which means I can't really work properly any more. I don't really want to go through the long process above, can anybody suggest why my profile might be making this change to the version number please?

What are you doing with your profile? If you downgrade to 128, you can delete the compatibility.ini file and resume normal processing. Your post indicates that you switch profiles and that is triggering the problem. At least, it appears to be the culprit.

I reported this exact same problem in a question last week, 10/3. David's very kind reply suggested I shouldn't believe my lying eyes - that 131.0 was only available from (un)authorized software distributors and could not have been automatically pushed to a production user. I've never in 15+ years of TB use, through numerous updates, ever been aware of receiving updates through a distributor.

Since then, (two days ago) I: - Uninstalled Thunderbird - Downloaded & reinstalled the currently supported release (128.3) from the Thunderbird.net site - Created the new esr profile it required me to do after preventing use of the most recent previous profile - Verified that the new 128.3 was on the .esr update channel, not "release" - Changed Thunderbird updates from "auto" to "check for updates, but let me choose to install" - Then exited

This morning, I launched Thunderbird and there it was -- 131.0 AGAIN. And with another new profile created today (ending in "default-esr") and back on the "release" update channel, but with updates still set to "check, but let me choose to install."

I'll either try David's suggestion to delete compatibility.ini or just restore from backup. Something is amiss, methinks.

I admit I was wrong in initial response. That was because 131 and prior monthly releases had not be released and were being downloaded from unauthoized sites. My error, as I had not noticed that 131 was now in public test mode. I apologize for any confusion on that initial response. Why you are being uploaded, however, is puzzling, unless you are changing profiles. I think, once you get to your primary profile that you will be ok.

David, you're a stand-up guy! Apologies, belg4mit, for hi-jacking your question, but it sounds like a number of us are encountering the same problem and reporting it as time goes on.

re. David's question on profiles, once 131 is uninstalled and 128.3 is downloaded & installed TB forces you to create a new (esr) profile. Once you do and then try to make your last production profile the "default" (or even launch it) TB returns you to the "create a new profile" or "exit" box and you can't proceed. But now, even with the new esr profile, TB will again auto-upgrade to 131, creating yet another new profile (default-esr) and returning the update channel to "release." All this with updates set to "check but do not install."

I am now of my depth on figuring out why this is happening. Need to restore from backup.

- when prompted to exit or create a new profile, EXIT - then, click to windows file explorer and the profile, and delete the compatibility.ini file - then, restart thunderbird and continue using your preferred profile.

Do no dispair. We are looking into how this could happen.

I just downloaded 128.3.0, was able to set my previous profile as default, and the issue appears to be fixed.

I took David's advice to delete compatibility.ini in my production profile and this probably facilitated the resolution. Did not need to restore from backup.

Good news. Thanks for sharing. :)

I have also applied David's fix and this does appear to resolve the problem, in that I now have a stable v 128 running that has not updated (yet) to v 131. Thanks David, and will report back if I have any more similar problems in future.

You're welcome. I suggest setting the auto-update to manual for awhile. There will then be the choice of using the monthly release or the extended release.