UI for login is clumsy

The app does work as intended and presentation is somewhat customizable. But the login UI could be much more user friendly. For example, it disappears when user attempts to use a password manager to login. And it disappears if the user clicks away in order to copy and paste from another app. Once the user does provide the user name and password, the button to submit is out of frame and the user has to find it using a horizontal scroll which is not obvious as there is no scroll bar shown in the popup. This can be very frustrating for the user. Instead of using the standard Facebook login, there should be a login created specifically for this messenger app that has an optimized user friendly UI.