It's about more than convenience. That same uniqueness reduces the chances that a password compromised on one site can be used on another -- intruders shouldn't have free rein with your accounts even if they punch through a site's defenses.

The functionality is useful right now in Mozilla's Firefox browser, and should come to both Google Chrome and Microsoft Edge in the "next few months." Opera has also publicly committed to the technology (there's no mention of Apple bringing it to Safari). No, you can't immediately forego all your passwords, but this could let you depend on biometric logins much more consistently than you have in the past.