Site URL: <select id="urlHeader">
<option value="https://">https://</option>
<option value="http://">http://</option>
</select>
<input id="siteUrl" value="https://netflix.com" style="width:300px;"><span style="opacity:0;user-select:none;">______</span>
<input id="numTabs" type="number" value="5" min="2" max="10">

<br><br>
<button id="launch">Launch!</button>

<script>
var popupsEnabled = false;
popup();
function popup(){
  var tab = window.open('https://google.com');
  if (tab){
    tab.close();
    popupsEnabled = true;
  } else
    alert("Please enable popups for this site, then reload the page.");
}
const numTabs = function(){
  return document.getElementById('numTabs').value;
}
const urlHeader = function(){
  return document.getElementById('urlHeader').value;
}
const urlValue = function(){
  return document.getElementById('siteUrl').value;
};
const url = document.getElementById('siteUrl');
document.addEventListener('keyup', function(){
    if (urlValue().length < urlHeader().length || urlValue().substring(0,urlHeader().length) != urlHeader()){
      url.value = urlHeader();
    }
    if (numTabs() !== "" && (numTabs() > 10 || numTabs() < 2))
      document.getElementById('numTabs').value = 5;
    
});
document.getElementById('launch').addEventListener('click', function(){
  if (!popupsEnabled){
    alert("Please enable popups for this site, then reload the page.");
    return;
  }
  var x = [];
  var y = 1;
  for (var i = 0;i<numTabs();i++){
    x.push(window.open(urlValue()));
  }
  var interval = setInterval(function(){
    if (y == x.length - 1){
      clearInterval(interval);
    }
    x[y].close();
    y++;
  }, Math.round(600/numTabs()));
  
});
</script>