diff --git a/src/test/html/test_sandboxed.html b/src/test/html/test_sandboxed.html
index f0c485b5794..5db41761275 100644
--- a/src/test/html/test_sandboxed.html
+++ b/src/test/html/test_sandboxed.html
@@ -1,14 +1,10 @@
 <html>
 <body>
   <iframe sandbox="allow-scripts" src="test_sandboxed_iframe.html"
-          style="display:block; border: 1px; width: 400px; height: 400px"
-	  frameborder="yes"
-	  scrolling="yes"></iframe>
-hiiiiiiiii
+          style="display:block; border: 1px; width: 400px; height: 400px">
+  </iframe>
   <iframe sandbox="allow-scripts" src="test_sandboxed_iframe.html"
-          style="display:block; border: 1px; width: 400px; height: 400px"
-	  frameborder="yes"
-	  scrolling="yes"></iframe>
-byeeeeeeeeeeee
+          style="display:block; border: 1px; width: 400px; height: 400px">
+  </iframe>
 </body>
 </html>
diff --git a/src/test/html/test_sandboxed_iframe.html b/src/test/html/test_sandboxed_iframe.html
index 210a6134a1b..d4dbb045ea7 100644
--- a/src/test/html/test_sandboxed_iframe.html
+++ b/src/test/html/test_sandboxed_iframe.html
@@ -1,24 +1,65 @@
 <html>
 <body>
   <script>
-    var a = 1;
-    var b = 1;
-    var c = 2;
-    var step = 1;
-    window.alert(Date.now());
-    var next = new Date();
-    window.alert(next);
-    while (true) {
-      if ((new Date()) >= next) {
-        window.alert("step " + step + ": " + c);
-        a = b;
-        b = c;
-        c = a + b;
-        step++;
-        next = new Date(Date.now() + 500);
-      }
+function Matrix(ary) {
+    this.mtx = ary
+    this.height = ary.length;
+    this.width = ary[0].length;
+}
+
+Matrix.prototype.toString = function() {
+    var s = []
+    for (var i = 0; i < this.mtx.length; i++)
+        s.push( this.mtx[i].join(",") );
+    return s.join("\n");
+}
+
+Matrix.prototype.mult = function(other) {
+    if (this.width != other.height) {
+        throw "error: incompatible sizes";
     }
+
+    var result = [];
+    for (var i = 0; i < this.height; i++) {
+        result[i] = [];
+        for (var j = 0; j < other.width; j++) {
+            var sum = 0;
+            for (var k = 0; k < this.width; k++) {
+                sum += this.mtx[i][k] * other.mtx[k][j];
+            }
+            result[i][j] = sum;
+        }
+    }
+    return new Matrix(result);
+}
+
+function run() {
+  var now = new Date();
+  var div = document.getElementsByTagName('div')[0];
+  var elems = [];
+  for (var i = 0; i < 900; i++) {
+    elems.push(i);
+  }
+  var outer = [];
+  for (var i = 0; i < 900; i++) {
+    outer.push(elems);
+  }
+  var a = new Matrix(outer);
+  var b = new Matrix(outer);
+  var result = a.mult(b);
+  var time = (new Date()) - now;
+  var text = document.createTextNode(time.toString() + 'ms');
+  var para = document.createElement('p');
+  para.appendChild(text);
+  div.appendChild(para);
+}
+
+setTimeout(function forever() {
+  run();
+  setTimeout(forever, 3000);
+}, 0);
   </script>
-hi there
+<p>Time required to multiply two 900x900 matrices:</p>
+<div></div>
 </body>
 </html>
