Hi,
Whenever you launch pgAdmin 4 in runtime mode, it will open in your system's default browser. If you want to open the application in another browser then you can set that with pgAdmin 4 Tray Icon > Configure window.
Regarding the Unauthorised error, as Dave said in the same email thread :
You can expect to see 401's if you're running pgAdmin in desktop mode, and try to connect without using the security key. Running under the runtime should prevent that happening.
In server mode, you should always be redirected to the login page if you need to authenticate (and the security key isn't used).
Thanks,
Khushboo