old_contents: /*global $, Whisper, Backbone, textsecure, extension*/
  /*
   * vim: ts=4:sw=4:expandtab
   */
  (function () {
      'use strict';
  
      function logError(error) {
          extension.windows.getBackground(function(bg) {
              bg.console.log('index.html: ', error);
          });
      }
  
      window.onerror = function(message, script, line, col, error) {
          logError(error);
      };
  
      function render() {
          extension.windows.getBackground(function(bg) {
              bg.owsDesktopApp.getAppView(window).then(function(appView) {
                  var bodyEl = document.getElementById('signal-container');
                  bodyEl.innerHTML = "";
                  bodyEl.append(appView.el);
              });
          });
      }
  
      window.addEventListener('onreload', render);
      render();
  }());
  
new_contents: /*global $, Whisper, Backbone, textsecure, extension*/
  /*
   * vim: ts=4:sw=4:expandtab
   */
  (function () {
      'use strict';
  
      function logError(error) {
          extension.windows.getBackground(function(bg) {
              bg.console.log('index.html: ', error);
          });
      }
  
      window.onerror = function(message, script, line, col, error) {
          logError(error);
      };
  
      function render() {
          extension.windows.getBackground(function(bg) {
              bg.owsDesktopApp.getAppView(window).then(function(appView) {
                  var bodyEl = document.getElementById('signal-container');
                  bodyEl.innerHTML = "";
                  bodyEl.appendChild(appView.el);
              });
          });
      }
  
      window.addEventListener('onreload', render);
      render();
  }());
  
subject: Use appendChild instead of append