I have a project done with Firebase and Js where I occupy loggin with the Firebase Authentication, when you log in you go to another screen, I realized that if I copy the link of my new screen, I close session and I paste the link in my browser re-directs me to that screen without asking me for a new loggin. Try with the firebase.auth (). CurrentUser; give a condition with an if know if the user is nullo send me to the loggin and if it is correct I can continue doing everything that my code does.
var user = firebase.auth().currentUser;
if (user == null) {
console.log("usuario nullo");
window.open("index.html", "_self", true);
} else { //Usuario Activo
//Codigo