Would you consider the KeePassHTTP solution to be adequate (they have a browser plugin that acts as a password manager using the browser's APIs and the passwords are retrieved after authenticating the plugin with the KeePassXC server -- which prompts the user each time and only entries that match the URL are sent).

They also support copying the password to your clipboard (which they then clear after a few seconds). There's also the automated entry system which basically emulates keystrokes.