Good thing we publish a simple process for removing the primary password hey. https://support.mozilla.org/en-US/kb/protect-your-thunderbird-passwords-primary-password#w_removing-your-primary-password

Just to be clear, uninstalling and reinstalling will do exactly nothing in this situation.

Hi Matt, As we don't know each other, I have to tell you, in short, that I 'm not a newbie on computers. As a result your link doesn't learn me anything new, personally. Thanks anyway. But when you say that removing and reinstalling Thunderbird in Windows won't help, that's something I wasn't aware of. Do I have to suppress manually some files or some profile somewhere? Tell me please what I could do, in your view, if I can, in order to get out of this situation and to use Thunderbird again on my desktop PC. (I'm absolutely NOT "hijacking" somebody else PC!) I repeat that I don't have any problem about IDs/ passwords of my different emails. I should have pay much more attention when typing my new password, no doubt. BTW, guys, take much much care when modifying any password! TB still works normally on my other PC, my laptop. Of course, I didn't do any mistake when modifying the Password on this PC. I prefer TB to the web pages, though not for all my emails, it's simply a question of comfort. To tell you everything, I have an old glasses issue since a while, and that makes me do a lot of errors :( Thank you Matt.

I provided you a link to instructions removing or resetting the primary password if you do not know it, as you appear to not know what you set the password to.

Here it is again in French https://support.mozilla.org/fr/kb/proteger-thunderbird-avec-mot-de-passe-principal#w_supprimer-le-mot-de-passe-principal

As you have only one choice when you do not know the primary password. That being reset it/Remove it and in the process clear the stored passwords and any oath tokens stored in the password manager.

I really do not understand what more I can tell you. The way forward it simple. You have to reset the password using the instruction on the web page.

Thanks a lot pal! You have been super helpful. Thanks a lot. The second half of the page explains how to remove the password. Afterward I inserted my email passwords, one by one, by copy-paste (easy thanks to my password manager) You nicely sent me the page in French, it seems. Actually my Desktop PC is set in English since ten years. (I couldn't speak English before). My laptop is in French.

A small advice to people: When changing a password anywhere proceed only by copy-paste, don't type directly. Open, for example, "Notepad" and type the password in clear. You see what you are typing. You will avoid what happened to me. And, by the way, when changing the "master password" in a password manager, in case of mistake you can lose completely the access to your vault and there's no way out! Have a good day :)