Use textContent instead of innerText.

experimental/webtry/js/run.js

 /**
  * Common JS that talks XHR back to the server and runs the code and receives
  * the results.
  */
 
 /**
  * A polyfill for HTML Templates.
  *
  * This just adds in the content attribute, it doesn't stop scripts
  * from running nor does it stop other side-effects.
@@ skipping 54 matching lines @@
     /**
      * Callback when there's an XHR error.
      * @param e The callback event.
      */
     function xhrError(e) {
       endWait();
       alert('Something bad happened: ' + e);
     }
 
     function clearOutput() {
-      output.innerText = "";
+      output.textContent = "";
       if (stdout) {
-        stdout.innerText = "";
+        stdout.textContent = "";
       }
       embed.style.display='none';
     }
 
     /**
      * Called when an image in the workspace history is clicked.
      */
     function historyClick() {
       beginWait();
       clearOutput();
@@ skipping 46 matching lines @@
       // {
       //   "message": "you had an error...",
       //   "img": "<base64 encoded image but only on success>"
       // }
       //
       // The img is optional and only appears if there is a valid
       // image to display.
       endWait();
       console.log(e.target.response);
       body = JSON.parse(e.target.response);
-      output.innerText = body.message;
+      output.textContent = body.message;
       if (stdout) {
-        stdout.innerText = body.stdout;
+        stdout.textContent = body.stdout;
       }
       if (body.hasOwnProperty('img')) {
         img.src = 'data:image/png;base64,' + body.img;
       } else {
         img.src = '';
       }
       // Add the image to the history if we are on a workspace page.
       if (tryHistory) {
         addToHistory(body.hash, 'data:image/png;base64,' + body.img);
       } else {
@@ skipping 37 matching lines @@
 
 
     // Add the images to the history if we are on a workspace page.
     if (tryHistory && history) {
       for (var i=0; i<history.length; i++) {
         addToHistory(history[i].hash, '/i/'+history[i].hash+'.png');
       }
     }
 
 })(workspaceName);