Y How do I go back???

You don't!

This might help. https://thunderbirdtweaks.blogspot.com/2019/09/i-lost-my-profilemail-on-update-to.html

ONCE YET AGAIN Mozilla, as with the update 91.3.2 just last month you have really screwed the pooch on this one (91.4.0). It wiped out both accounts, wiped out all the changes I had made to it, & wiped out my entire address book. You get a big fat zero on the 1 to 10 scale. Two updates in 2 months do the exact same thing??? What is wrong there at Mozilla that updates do this??? This is totally unacceptable!!! FIX YOUR PROBLEM!!! I like Thunderbird BUT I had rather go back to using Outlook 2007 than put up with this behavior. FIX IT!!!

Ever wondered why some folks have issue and others have none? Usually it has a lot to do with how they have configured their computer and security software.

For instance to you have an anti virus scanning in the Thunderbird profile and potentially locking access to files? What about having moved he profile folder to somewhere that backs up? Most windows users do have anti virus busy messing in places they have to right to be, and then wonder why updates can't be written cleanly. While there are occasional shocker updates, no one is singling you out for special attention. I have gone through those same updates without an issue using windows 10 and windows defender.

Ever wonder why some people on some support(?) forums seem to attack/accuse the poster rather than try to help? No one is singling you out for special attention...

in answer to your post, none of the above. This is a new computer, new install of windows, new install of anti-malware, new install of firewall; no tweaks/adjustments made to any of them, and yet...

mozilla coders need to scrutinize their code. When I opened TB today it updated and looked exactly as if I had just installed it for the first time.

Goodbye Thunderbird. You were once a good product.

If you start Thunderbird with Profile Manager, you probably will find your information is till there. There is also normally a backup of prefs.js

I just reread your second posting which states "Two updates in 2 months do the exact same thing???"

I don't know exactly what caused this, but Thunderbird isn't in the habit of losing profiles on update - so on that point I agree with Matt. This isn't saying it is your fault, but please know that without more details it's impossible to say what happened, as you didn't help with a reply after Matt posted to your problem with https://thunderbirdtweaks.blogspot.com/2019/09/i-lost-my-profilemail-on-update-to.html

Unfortunately this information is way out of date... it talks about ver. 67 - 68 while current is 91.4.0. The pictures shown do not even match current ver. Using the command line option that someone else had used I was able to find and select the profile needed and - hallelujah - things look normal. BUT!!! Wiping things out the way it did TWICE, SHOULD NEVER HAVE HAPPENED. And as someone else said, It shouldn't take hacker status to fix or workaround the problem.

Unfortunately this information is way out of date... it talks about ver. 67 - 68

Given nothing at all has changed, profile per install still being enforced and still loosing profiles since 68 the information is factual. I can not help it is you have issues it is not a new issue and your assumnption it is is the root of your complaint that it is out of date. Why you got it twice is almost certainly down to how you configure your system, or your choice of security software but certainly nothing I can influence. But I do not consider the why all that relevant. The issue for me is helping folk recover.

Concerned I was pointing people to wrong information I have just worked through that blog post and I find nothing that I would consider requires amending with regards to details. I will continue to post the link because it is still relevant. That a couple of the screen images are now HTML and at the time of writing were XUL is irrelevant as the words in them are exactly the same as they were in V68. But the post is years old, so some aging of images is to be expected. You are welcome to write an article that contains current images in the knowledge base here on Mozilla support. https://support.mozilla.org/en-US/kb/create-new-knowledge-base-article I will not be, but if it is complete and accurate as to the steps to take I will link others to it. You can pick up the task on behalf of the user community as my efforts are inadequate.

If I assume that what you say is true... Wiping things out the way it did TWICE, SHOULD NEVER HAVE HAPPENED. And as someone else said, It shouldn't take hacker status to fix or workaround the problem.

And as I stated above - This is a new computer, new install of windows, new install of anti-malware, new install of firewall; no tweaks/adjustments made to any of them

"new install of anti malware." I am aware of at least three products known to make Thunderbird largely unusable out of the box depending on user choice of settings.

no tweaks/adjustments made to any of them

no tweaks/adjustments made to any of them

Is the Anti-Virus allowed to scan Thunderbird files and folders on start up, or opening of files or when download or uploading of files ? If yes, then it can cause problems. So you may need to tweak settings. Recommend you do not allow any AV to scan Thunderbird files and folders. If you do allow scanning then at least do not use an auto fix option, so you can tell AV to do nothing.

Do you have any 'Clean up' software like CCleaner or WiseCleaner or some Anti-Virus products have the ability - if yes, then you need to exclude Thunderbird profile folders and files.

RE: as with the update 91.3.2 just last month you have really screwed the pooch on this one (91.4.0). It wiped out both accounts, wiped out all the changes I had made to it, & wiped out my entire address book.

I presume Thunderbird looks like it's new and wants you to add mail accounts. Either it has lost the profile or lost the 'prefs.js' file, so this information we need in order to have a better idea about what is going on. It is very unusual to keep losing profiles, so something is amiss. First check is always going to be Anti-Virus / Anti-Malware /Clean up type of software as it can cause havoc.

But then we need to know whether the profile really is lost or just not being displayed. To do this you need to supply some useful information by following these instructions.

It would be helpful to know what you have got stored in this location: In Thunderbird

• Menu app icon > Help > More Troubleshooting Information
• Under 'Application Basics' - locate 'Profile Folder' and click on 'Open Folder'

A new window opens showing the contents of your 'Profile name' folder which is located here: C:\\Users\User Name\Appdata\Roaming\Thunderbird\Profiles\'profile name'

• Exit Thunderbird now.

• Make sure you have the view showing details, so there is are Name, Type, Size, Modified date columns.
• Scroll down and locate 'prefs.js' file.

Q: Do you see more files of same name with a number attached eg: 'prefs-1.js', 'prefs-2.js' etc ? Q: How many of them do you see? Q: Do some have a zero size ? Do some have a good KB size like 70KB? Post a jpg image showing what you see.

Then go up a directory level to the 'Profiles' folder. Post an image showing the contents of the 'Profiles' folder.

Then go up a directory level to the 'Thunderbird' folder. You will see a 'profiles.ini' file. Open it using a simple text editor like Notepad. Post an image showing the contents.

RE: Using the command line option that someone else had used I was able to find and select the profile needed and - hallelujah - things look normal. Toad_Hall, your information is all well and good. But it just re-enforces what I have said; it should never have happened. And it shouldn't take "hacker status" to fix/workaround this problem. I never had a problem with updates prior to 91.3.2. I have disabled automatic updates and we will see what happens next update. Thanks to all.