In version 60 you shouldn't need an addon anymore to prevent multiple password prompts

Thank both of you for helpful comments. I tried changing the maxVersion and zipping it up again but I still get the same result. I don't actually need to enter both password prompts as one seems to work fine. But the 2nd request window stays open until closed manually.

I've now removed Startup Master.

I'd like a password prompt at the front where you can't even open the client (Thunderbird) without entering a password.

Are you saying you still get two Master Password prompts with TB60? This is what I'm seeing too. The Startup Master extension works still fine here with TB60.

Yes, two password prompts. I did get that with Startup Master which I have now uninstalled. Still the same with TB60. I don't need to complete both prompts; I'm authenticated to all email accounts with just one response.

So is the second from an an asynchronous access to the password manager by Lightning to sync calendars.

Try restarting Thunderbird with add-ons disabled from the help menu. (don't permanently disable anything.)

Do you get one or two prompts in safe mode?

(I am thinking this might be calendar related. but a more broad sweep with all add-on disabled in safe mode will answer the question of if the source is an add-on.)

Still two password requests is safe mode. So problem is not with an add-on it seems.

I do use gContactSync and Provider for Google Calendar if that is any help.

Still two password requests is safe mode.

I can confirm that behavior for both, TB60 as well as TB64 beta.

I'm still using the Startup Master extension in TB60, but it's broken in TB64 beta.

Also see https://bugzilla.mozilla.org/show_bug.cgi?id=1176399#c142

So TBird seems to have an on-going problem with master passwords. Most people using it will have multiple email accounts and many will use the calendar of course.