After updating the system on my Macbook, Thunderbird won’t open because it wants a primary password which I have tried unsuccessfully to enter.

did you read the support article? https://support.mozilla.org/en-US/kb/protect-your-thunderbird-passwords-primary-password

That password only protect your passwords nothing else. Pressing escape on the keyboard will remove the initial request but the password manager will not be able to access your passwords until you either enter it or remove it. but that is all discussed in some detail in the support article.

I had already been to the link that was suggested above. I just uninstalled Thunderbird and re-downloaded the app. It still won't load. This email is being viewed through the apple main app.

Then if you have read the article you are fully informed on how to delete the primary master password. SO what are we discussing? Instead of removing the primary password it you apparently removed and reinstalled the application which by definition does not affect your settings..

Thunderbird will not start and I have set up a Primary Password because I have not used one and now, also deleted it. I have uninstalled the old version of Thunderbird and reinstalled the current one and have the same results. It wants a Primary Password to load, but when I set one up in Firefox, it does not work. I have tried to load it in Troubleshoot mode and it still won’t load. Is it no longer compatible with the current OS for the MacBook? Thanks, Anne