It might be helpful to know which services that you have signed up for that use a Firefox Account. I see no "connection" between "Sign in" and "Sign out" with any the services that affects any other service. IOW, being signed in on one doesn't have you signed in on all services.

https://support.mozilla.org/en-US/kb/access-mozilla-services-firefox-accounts Sorry nothing there that explains a logo out or at least logging out of them all in "one fell swoop."

Caution - reading further just might serve to confuse you, not help you.

If you are using Firefox Accounts for the Sync service, you can hit the 3-bar button on the right-side of the Navigation Toolbar to open the Menu Panel. Then click the email address for your Sync account / Firefox Account to log out from there.

Each of these three websites are completely separate from my Sync log in using Firefox Accounts, and separate from each other.

https://discourse.mozilla-community.org/ - the Add-ons support website does use a Firefox Account, but that log in is 'held' separate from all the others. Log in to use it fully and log off from there, too. And that one is still using the old Persona "brand" for Firefox Accounts.

https://testpilot.firefox.com/ - about the same thing. Sign in to use the test-pilot features on that page with the Test Pilot extension and then Sign out when you're done, if you want to be "out".

Similar for the Bugzilla web site. https://bugzilla.mozilla.org/

I too wish to log out of my "Firefox account" i.e. the account for the Firefox browser. I wish to do this because I want to check my Log in credentials since I am now utterly confused between Firefox, the Mozilla S|upport log-in and the "Master password for the Softrware Security Device"