I just wanted a standard data exchange interface between my browser and my preferred password manager, so that my password manager didn't have to try to emulate a human being typing or pasting a password.

That way the password would only "live" in the password manager and wouldn't need to even be easily visible to me. I almost never care what the password actually is.

But it would still be a password so compatible with most sites as-is, and easily backed up and restored on new devices.