If you filter by email address, does anything comes that might be what you are after ?

You can check the logins.json file in the profile folder to see whether this login is stored as a hidden entry similar to the Firefox Account credentials.

• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

It certainly isn't under the Passwords. I copied the login.json file into Word and searched there. Nothing Microsoft, though I found many other web entries; all with encryped passwords so it wouldn't have helped.

I wonder if, somewhere in the past, some connected files got lost. I do copy the Profile folders around to my back-up drives and another laptop I rarely use.

But it does beg the question as to where Firefox is getting the password.

Have you tried looking for the login URL domain as shown in the address bar, in the password manager? (you may wish to remove the https:// part, and any trailing /s).

I know that sometimes the Microsoft Account login page URL doesn't actually contain the name Microsoft, hence this name might not be associated with that login in the password manager.

Suggestions in a login drop-down list that have a key icon in front are login suggestions that you need to remove in the Password Manager.

• https://support.mozilla.org/en-US/kb/password-manager-remember-delete-edit-logins

Suggestions in a drop-down list without a key symbol are autocomplete saved form data. Suggestions without a key icon are part of autocomplete saved form data that you should be able to remove by selecting this item with the cursor Down key and pressing Delete (Mac: Shift+Delete).

• https://support.mozilla.org/en-US/kb/control-whether-firefox-automatically-fills-forms

Thanks to everone's input.

In the end I did find the password under Passwords where they were supposed to be (apologies). It wasn't until I went through them in detail, although thinking that was a waste of time.

While all my passwords are under their obvious respective labelled websites, Microsoft is not.

The Microsoft password is located under login.live.com. Below the web address is the email address associated with the Microsoft account. So you won't fint the word Microsoft anywhere, including in the login.json file.

I've learned something.

Regards Hans