These tokens are Google OAuth2 refresh tokens (see bullet 4 in Google Identity Platform). Their number is limited (i guess it is 25 ).
The easiest way to explicitly revoke a token is to use firebase logout --token <token>
as you mentioned. I do not know of an API for listing outstanding refresh tokens, I'm not sure it exists.
But I do know that clicking 'Remove' on the Firebase CLI entry here: https://myaccount.google.com/permissions will revoke the active tokens.
Logging back in will prompt you for permissions again and if you grant them your new token will be the only valid one.
So, It's better to remove permission from your App permissions, so no leftover tokens are there on your project.