You'll need to find and close the application that's hogging up usage of your webcam. Make sure other communication applications or tabs in your browser are not running.
Just for now ignore Firefox, the icon you see is normal, because the "Entrar" button is disabled.
First the camera and mic must be detected and allowed. Then once this is solved, you will enter the meeting automatically. I suggest getting technical support for the camera first as this should solve everything else.