// get a reference to the install button
var button = document.getElementById('install-btn');

if(navigator.mozApps) {

var manifest_url = location.href + 'manifest.webapp';

function install(ev) {
  ev.preventDefault();
  // define the manifest URL
  // install the app
  var installLocFind = navigator.mozApps.install(manifest_url);
  installLocFind.onsuccess = function(data) {
    // App is installed, do something 
  };
  installLocFind.onerror = function() {
    // App wasn't installed, info is in
    // installapp.error.name
    alert(installLocFind.error.name);
  };
};

//call install() on click if the app isn't already installed. If it is, hide the button.

var installCheck = navigator.mozApps.checkInstalled(manifest_url);

installCheck.onsuccess = function() {
  if(installCheck.result) {
    button.style.display = "none";
  } else {
    button.addEventListener('click', install, false);
  };
};

} else {
  button.style.display = "none";
}