Append "name" and "final score" of a quiz game to an alert("") message

Upon submitting the "Name" of the user after finishing the quiz I need the alert message to show his/her numerical standing based on their quiz score with the name they submitted. One of the minor issues I am encountering is that the alert reads back to me 

[object HTMLInputElement] Where the "Name" of the user should be. 

<pre>const startButton = document.getElementById('start-btn');
const nextButton = document.getElementById('next-btn');
const scoreButton = document.getElementById('score-btn');
const questionContainerElement = document.getElementById('question-container');
const questionElement = document.getElementById('question');
const answerButtonsElement = document.getElementById('answer-buttons');
const scoreTracker = document.getElementById('score-tracker');
const scoreUpElement = document.getElementById('score-up');
var firstName = document.getElementById('firstname');
var submitForm = document.getElementById('submit-form');

let randomQuestions, currentQuestionIndex;

startButton.addEventListener('click', startGame);
nextButton.addEventListener('click', () => {
  currentQuestionIndex++
  setNextQuestion()
});
/*scoreButton.addEventListener('click', scoreList);*/

function startGame() {
  startButton.classList.add('hide');
  randomQuestions = questions.sort(() => Math.random() - .5);
  currentQuestionIndex = 0;
  questionContainerElement.classList.remove('hide');
  scoreTracker.classList.remove('hide');
  setNextQuestion();
  scoreUpElement.textContent = 0;
  scoreButton.classList.add('hide');
};

function setNextQuestion() {
  resetState();
  showQuestion(randomQuestions[currentQuestionIndex]);
};

function showQuestion(question) {
  questionElement.innerText = question.question;
  question.answers.forEach(answer => {
    const button = document.createElement('button');
    button.innerText = answer.text;
    button.classList.add('btn');
    if (answer.correct) {
      button.dataset.correct = answer.correct;
    }
    button.addEventListener('click', selectAnswer);
    answerButtonsElement.appendChild(button)
  })
};

function resetState() {
  clearStatusClass(document.body);
  nextButton.classList.add('hide');
  while (answerButtonsElement.firstChild) {
    answerButtonsElement.removeChild(answerButtonsElement.firstChild)
  }
};

/* Checks if selected button is part of the correct dataset */
function selectAnswer(e) {
  const selectedButton = e.target;
  const correct = selectedButton.dataset.correct;
  
  processResults(correct);
  setStatusClass(document.body, correct);

  Array.from(answerButtonsElement.children).forEach(button => {
    setStatusClass(button, button.dataset.correct)
  })

  if (randomQuestions.length > currentQuestionIndex + 1) {
    nextButton.classList.remove('hide');
  } else {
    startButton.innerText = 'Restart';
    startButton.classList.remove('hide');
    scoreButton.innerText;
    scoreButton.classList.remove('hide');
  }
};

function setStatusClass(element, correct) {
  clearStatusClass(element);
  if (correct) {
    element.classList.add('correct');
  } else {
    element.classList.add('wrong');
  }
};

function clearStatusClass(element) {
  element.classList.remove('correct');
  element.classList.remove('wrong');
};


/* Game questions with 4 total choices */
let questions = [{
    question: 'What year did the Raiders win their last Super Bowl?',
    answers: [{
        text: '2003',
        correct: true
      },
      {
        text: '1993',
        correct: false
      },
      {
        text: '1983',
        correct: false
      },
      {
        text: '1972',
        correct: false
      },
    ]
  },
  {
    question: "What was Jack Tatum's nickname?",
    answers: [{
        text: 'Killer Croc',
        correct: false
      },
      {
        text: 'The Assassin',
        correct: true
      },
      {
        text: 'The Jackhammer',
        correct: false
      },
      {
        text: 'Killer Bee',
        correct: false
      },
    ]
  },
  {
    question: "Which 'Hall of Fame' Raider wore the number 00",
    answers: [{
        text: 'Charles Woodson',
        correct: false
      },
      {
        text: 'Kenny Stabler',
        correct: false
      },
      {
        text: 'Mike Haynes',
        correct: false
      },
      {
        text: 'Jim Otto',
        correct: true
      },

    ]
  },
  {
    question: 'Which Raider became a HollyWood star?',
    answers: [{
        text: 'Carl Weathers',
        correct: true
      },
      {
        text: 'Howie Long',
        correct: false
      },
      {
        text: 'Lyle Alzado',
        correct: false
      },
      {
        text: 'Bo Jackson',
        correct: false
      },
    ]
  },
  {
    question: 'Who is Al Davis?',
    answers: [{
        text: 'Current star Wie Receiver',
        correct: false
      },
      {
        text: 'Current Owner',
        correct: false
      },
      {
        text: "QB from the late 70's",
        correct: false
      },
      {
        text: 'Ex Owner',
        correct: true
      },
    ]
  },
];


function processResults(isCorrect) {
  if (!isCorrect) {
    return;
  }
  
  const scoreUp = parseInt(scoreUpElement.textContent, 10) || 0;

  scoreUpElement.textContent = scoreUp + 100;
};

/*submitForm.addEventListener('click', formSubmission)*/

var scoreNames = [];

function formSubmission() {
  firstName.innerText
  if (confirm('Do you want to submit')) {
    alert(`Congrats ${firstName} you won!`)
  } else {
    return false;
  };


};




/*function formSubmission() {
  if (confirm('Do you want to submit')) {
    document.getElementById('submit-form');
  } else {
    return false;
  };


};*/

/*function store() {
  localStorage.setItem('name', name.value);
}*/

<pre><!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <link rel="stylesheet" href="assets/css/scores.css" />
    <script defer src="assets/js/script.js"></script>
    <title>High Scores</title>
  </head>

  <body>
    <div id="container-username">
      <div id="container-title">
        <h3>Type your name to see your score!</h3>
        <div>
            <form onsubmit="return formSubmission()">
            <input type='text' id='firstname' name='firstname' required />
            <input type='submit' id="submit-form" value="Go Now!">
            </form>
        </div>
    </div>
  </body>
</html>

<pre><!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <link rel="stylesheet" href="assets/css/scores.css" />
    <script defer src="assets/js/script.js"></script>
    <title>High Scores</title>
  </head>

  <pre lang="CSS">* {
    box-sizing: border-box;
    font-family:'Times New Roman', Times, serif;
}

:root{
    --hue-neutral: 213;
}

body {
    --hue: var(--hue-neutral);
    padding: 0;
    margin: 0;
    display: flex;
    width: 100vw;
    height: 100vh;
    justify-content: center;
    align-items: center;
    background-color: hsl(var(--hue), 31%, 19%);
} 

#container-username {
    width: 800px;
    max-width: 80%;
    background-color: #63768d;
    border-radius: 5px;
    padding: 10px;
    box-shadow: 0 0 10px 2px;
}

#container-title {
    text-align: center;
}

#username {
    text-align: center;
}

.center-me {
    text-align: center;
}

/*function formSubmission() {
  if (confirm('Do you want to submit')) {
    document.getElementById('submit-form');
  } else {
    return false;
  };


};*/

/*function store() {
  localStorage.setItem('name', name.value);
}*/