I do not see what logging into the Mozilla support site has to do with your emails. They are unrelated.

The password for your email will be whatever you provider issues and has nothing to do with Mozilla or any website they maintain at all.

Ok - thanks for the clarification. But my problem remains. I reinstalled Windows and now Thunderbird on my desktop and do not have my password nor user name. I thought I did because my I phone e-mails through TB mirrored what I had on my desktop but when I use my I phone log in credentials - user name and password - on my desktop, I get an authentication error. I cannot create a new account with my current e-mail which I have had for many decades so I am stuck.

One followup - so TB had prefilled my incoming and outgoing server under Configuration Found in Mozilla ISPDB. It shows the IMAP incoming server settings and my correct e-mail address under the "user name" as well as the SMPT outgoing server settings. But no matter what password I try (even the one from my phone) , it does not work.

So right now I cannot access my e-mails on my desktop.

if you want support an excellent starting point is to actually say what mail provider you use. There are some particularly painful ones out there not the least of which is Microsoft and their outlook offering. Yahoo is a mess if this support forum is anything to go by. So who are we dealing with.

Do you have an antivirus? They are number one on the list of things that prevents the adding of a mail account. Do you use any sort of other security software like a VPN or ccleaner? They are also chronically involved in making adding an account difficult.

You will notice I do not mention Thunderbird here. That is because it is most rare for Thunderbird actually be the problem. So the starting point is always third party product and their associated helper applications and security breaking use of self signed certificates.

The disabling of cookies and blocking access to localhost form another raft of failures that again have nothing or little to do with the way Thunderbird installs and are often the result of misguided security settings.