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.
The hard problem is getting the passwords out of the encrypted store and into form fields in your browser.