> You must be joking.

You must be joking, are you still not using a password manager at all?

When you create the username+password combo you either do it yourself, then put in the password manager the domain, or you use whatever the password manager infers at the registration page, then that's basically it, for most sites. Then 1% of the websites insist to use signin.example.com for login and signup.example.com for signup, so you add both domains to your password manager, or example.com.

Now whenever you login, you either see a list of accounts (means you're on the right domain) or you don't (which means the domain isn't correct). And before people whine about "autofill doesn't always work", it doesn't matter, the list should (also) show up from the extension modal/popup, so even if autofill doesn't work for that website, you'd be protected, since the list of accounts are empty for wrong domains.

It's really easy, and migrating to a password manager just sucks the first couple of days, every day after that you'd be happy you finally did it.