Unlike the behavior in other browsers such as Brave and Safari, the login window for 1Password as part of the Firefox add-on doesn't show the main 1Password window after logging in. You supply the password (either by typing or with TouchID) and then have to click the add-on button again to get it to display again. In other browsers, you click the button and the login prompt shows on top of the other frame so your logins are visible without a second click. I know this bug was addressed a while back but it appears that it either didn't apply to Firefox or it was reintroduced at some point.
1Password Version: 1Password 7 Version 7.9.2 (70902005)
Extension Version: 2.1.4
OS Version: macOS 12.0.1 (21A559)