Perhaps you might like to leave feedback in the feedback forum for the developers https://connect.mozilla.org there is also a link on the help menu in Thunderbird to that address. Airing your angst in a peer support forum does not get the message to the developers, only to fellow users like myself.

I assume something went wrong with the update. If you want support in fixing your migration so 115 works, I will do what I can. But I am done helping people to go backwards to an unsupported version. This forum and my blog has plenty of discussion on how going back commencing with the release of V68 is done, including full discussion on the topic.

Thank you for the clarification as to which forum is for what - because, the design and wording indicates to me the exact OPPOSITE.

support.mozilla.org menus: "Support, Get Help, Contribute" makes me think I'm dealing with developers where I can get support, get help, and possibly contribute to new version of the app.

connect.mozilla.org menus: "Connect, Ideas, Discussion, Community" indicate that I'm Connect-ing with a Community of fellow users to Discuss, share Ideas.

Clearly the design and wording of the two very similar sites is NOT clear enough to new users as to which is for what. A simply byline "Your connection to the development team" "Support from fellow end users" would go a LONG way to clearing that up.

I figured out how to go back. (posting for anyone who hits my OP.

Yay TextEdit. Almost as good as ResEdit. ;-)

In the Profile folder: Compatibility.ini has a version line. prefs.js has the app version noted three times. prefs.js also has a line "lastAppBuildId"

I changed the content on those lines, in my preferred, but not working profile, to content on those same lines from a new, empty profile created in 102. Launched Thunderbird 102, and it loaded my default profile without issue.

See also: https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-thunderbird-profiles To properly set your old profile as the default.

TYVM.

Congratulations. A hard way to do what would occur if you used the allow-downgrade command line when starting Thunderbird. I refuse to mess with the downgrade brigade, you made your choice and will have to live with whatever corruption that has created. But, I will not now, or ever promote it as a reasonable approach to change. Data loss and corruption are not acceptable to me. Sorry.

You still have not downgraded your data and some at least will have been lost. I am not across what this particular version will have left in a newer file format, but calendars, contacts, passwords and mail data are all in the process of changing. What you don't have now is something you will perhaps not work out for a long time, like the inability to save a changed password. But there will almost certainly be issues resulting from your decision.

I could not find an official Mozilla procedure for end users (not developers) to downgrade. If there is, your comment would have been better served to provide a link to the Mozilla document explaining proper way to go from 115 back to 102.

Given the fact that installing 115 took zero time to update "all my data... file format, passwords" I suspected that there was not actually any update to my data, just to the interface that looked at it. Moreover, I had done nothing but get mail a few times in 115, to realize it was not for me, and use my procedure to go back.

I have now been doing everything for 18 days since I went back to 102. I have had zero issues on multiple e-mail accounts, from multiple systems, with e-mail going back over a decade.

As I said, this much content can not be instantly converted to something else. It would have to take time to migrate the data. But the switch from 102 to 115 took zero time. I launched the app, and it was all there. There was no "conversion" of my mail / profile - which is actually the largest single folder on my computer.

This instant open indicates that nothing I have was "converted" and nothing needed to be "un-converted" except the prefs file that prevented 102 from opening my profile. I reserve the right to be wrong. I use Thunderbird for mail, not calendaring, task, chat, ...

If you have evidence to specific "data-loss and corruption resulting from my decision" then post it. Saying "some will have been lost" is vague and unhelpful to me, and any other reader finding this thread.

To matt developers don't care about us end users who use thunderbird where it was ment for E-MAIL .. al rest we don't want .. this was for years a great e-mail program that would pull in the e-mail from hotmail (now outlook) with out having to deal with all the crap around it .. with this upgrade (that is painfully hard to turn back) thunderbird became a monster (not in a good way!)

I can not code when Firefox changed there whole browser and I asked for help cause i could not work with the new looks i basically got told to do make a few scripts very easy to learn By top contributers well end of that song was i had to find a other browser... now it seems to be going te same for thunderbird what i find terrible cause means i have to find a way to have all email folders to be moved over i have generated over the years..

So TY DEV's For Really screwing end users up!!!! By not giving a easy!!!!! option to revert back

To Vidpro am going to try to do what you described if i figure out what that all is !

other wise it be good bye Thunderbird as well