diff --git a/dom/events/Event-cancelBubble.html b/dom/events/Event-cancelBubble.html
new file mode 100644
index 00000000000000..43f83dc3b63b7b
--- /dev/null
+++ b/dom/events/Event-cancelBubble.html
@@ -0,0 +1,132 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Event.cancelBubble</title>
+  <link rel="author" title="Chris Rebert" href="http://chrisrebert.com">
+  <link rel="help" href="https://dom.spec.whatwg.org/#dom-event-cancelbubble">
+  <meta name="flags" content="dom">
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/testharnessreport.js"></script>
+</head>
+<body>
+  <div id="outer">
+    <div id="middle">
+      <div id="inner"></div>
+    </div>
+  </div>
+  <script>
+test(function () {
+  // See https://dom.spec.whatwg.org/#stop-propagation-flag
+  var e = document.createEvent('Event');
+  assert_false(e.cancelBubble, "cancelBubble must be false after event creation.");
+}, "cancelBubble must be false when an event is initially created.");
+
+test(function () {
+  // See https://dom.spec.whatwg.org/#concept-event-initialize
+
+  // Event which bubbles.
+  var one = document.createEvent('Event');
+  one.cancelBubble = true;
+  one.initEvent('foo', true/*bubbles*/, false/*cancelable*/);
+  assert_false(one.cancelBubble, "initEvent() must set cancelBubble to false. [bubbles=true]");
+  // Re-initialization.
+  one.cancelBubble = true;
+  one.initEvent('foo', true/*bubbles*/, false/*cancelable*/);
+  assert_false(one.cancelBubble, "2nd initEvent() call must set cancelBubble to false. [bubbles=true]");
+
+  // Event which doesn't bubble.
+  var two = document.createEvent('Event');
+  two.cancelBubble = true;
+  two.initEvent('foo', false/*bubbles*/, false/*cancelable*/);
+  assert_false(two.cancelBubble, "initEvent() must set cancelBubble to false. [bubbles=false]");
+  // Re-initialization.
+  two.cancelBubble = true;
+  two.initEvent('foo', false/*bubbles*/, false/*cancelable*/);
+  assert_false(two.cancelBubble, "2nd initEvent() call must set cancelBubble to false. [bubbles=false]");
+}, "Initializing an event must set cancelBubble to false.");
+
+test(function () {
+  // See https://dom.spec.whatwg.org/#dom-event-stoppropagation
+  var e = document.createEvent('Event');
+  e.stopPropagation();
+  assert_true(e.cancelBubble, "stopPropagation() must set cancelBubble to true.");
+}, "stopPropagation() must set cancelBubble to true.");
+
+test(function () {
+  // See https://dom.spec.whatwg.org/#dom-event-stopimmediatepropagation
+  var e = document.createEvent('Event');
+  e.stopImmediatePropagation();
+  assert_true(e.cancelBubble, "stopImmediatePropagation() must set cancelBubble to true.");
+}, "stopImmediatePropagation() must set cancelBubble to true.");
+
+test(function () {
+  var one = document.createEvent('Event');
+  one.stopPropagation();
+  one.cancelBubble = false;
+  assert_true(one.cancelBubble, "cancelBubble must still be true after attempting to set it to false.");
+}, "Event.cancelBubble=false must have no effect.");
+
+test(function () {
+  var outer = document.getElementById('outer');
+  var middle = document.getElementById('middle');
+  var inner = document.getElementById('inner');
+
+  outer.addEventListener('barbaz', function () {
+    assert_unreached("Setting Event.cancelBubble=false after setting Event.cancelBubble=true should have no effect.");
+  }, false/*useCapture*/);
+
+  middle.addEventListener('barbaz', function (e) {
+    e.cancelBubble = true;// Stop propagation.
+    e.cancelBubble = false;// Should be a no-op.
+  }, false/*useCapture*/);
+
+  var barbazEvent = document.createEvent('Event');
+  barbazEvent.initEvent('barbaz', true/*bubbles*/, false/*cancelable*/);
+  inner.dispatchEvent(barbazEvent);
+}, "Event.cancelBubble=false must have no effect during event propagation.");
+
+test(function () {
+  // See https://dom.spec.whatwg.org/#concept-event-dispatch
+  // "14. Unset event’s [...] stop propagation flag,"
+  var e = document.createEvent('Event');
+  e.initEvent('foobar', true/*bubbles*/, true/*cancelable*/);
+  document.body.addEventListener('foobar', function listener(e) {
+    e.stopPropagation();
+  });
+  document.body.dispatchEvent(e);
+  assert_false(e.cancelBubble, "cancelBubble must be false after an event has been dispatched.");
+}, "cancelBubble must be false after an event has been dispatched.");
+
+test(function () {
+  var outer = document.getElementById('outer');
+  var middle = document.getElementById('middle');
+  var inner = document.getElementById('inner');
+
+  var propagationStopper = function (e) {
+    e.cancelBubble = true;
+  };
+
+  // Bubble phase
+  middle.addEventListener('bar', propagationStopper, false/*useCapture*/);
+  outer.addEventListener('bar', function listenerOne() {
+    assert_unreached("Setting cancelBubble=true should stop the event from bubbling further.");
+  }, false/*useCapture*/);
+
+  var barEvent = document.createEvent('Event');
+  barEvent.initEvent('bar', true/*bubbles*/, false/*cancelable*/);
+  inner.dispatchEvent(barEvent);
+
+  // Capture phase
+  outer.addEventListener('qux', propagationStopper, true/*useCapture*/);
+  middle.addEventListener('qux', function listenerTwo() {
+    assert_unreached("Setting cancelBubble=true should stop the event from propagating further, including during the Capture Phase.");
+  }, true/*useCapture*/);
+
+  var quxEvent = document.createEvent('Event');
+  quxEvent.initEvent('qux', false/*bubbles*/, false/*cancelable*/);
+  inner.dispatchEvent(quxEvent);
+}, "Event.cancelBubble=true must set the stop propagation flag.");
+  </script>
+</body>
+</html>
diff --git a/dom/events/Event-dispatch-bubble-canceled.html b/dom/events/Event-dispatch-bubble-canceled.html
new file mode 100644
index 00000000000000..20f398f66f9bcf
--- /dev/null
+++ b/dom/events/Event-dispatch-bubble-canceled.html
@@ -0,0 +1,59 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title>Setting cancelBubble=true prior to dispatchEvent()</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+</head>
+<body>
+<div id="log"></div>
+
+<table id="table" border="1" style="display: none">
+    <tbody id="table-body">
+    <tr id="table-row">
+        <td id="table-cell">Shady Grove</td>
+        <td>Aeolian</td>
+    </tr>
+    <tr id="parent">
+        <td id="target">Over the river, Charlie</td>
+        <td>Dorian</td>
+    </tr>
+    </tbody>
+</table>
+
+<script>
+test(function() {
+    var event = "foo";
+    var target = document.getElementById("target");
+    var parent = document.getElementById("parent");
+    var tbody = document.getElementById("table-body");
+    var table = document.getElementById("table");
+    var body = document.body;
+    var html = document.documentElement;
+    var current_targets = [window, document, html, body, table, tbody, parent, target];
+    var expected_targets = [];
+    var actual_targets = [];
+    var expected_phases = [];
+    var actual_phases = [];
+
+    var test_event = function(evt) {
+        actual_targets.push(evt.currentTarget);
+        actual_phases.push(evt.eventPhase);
+    };
+
+    for (var i = 0; i < current_targets.length; ++i) {
+        current_targets[i].addEventListener(event, test_event, true);
+        current_targets[i].addEventListener(event, test_event, false);
+    }
+
+    var evt = document.createEvent("Event");
+    evt.initEvent(event, true, true);
+    evt.cancelBubble = true;
+    target.dispatchEvent(evt);
+
+    assert_array_equals(actual_targets, expected_targets, "actual_targets");
+    assert_array_equals(actual_phases, expected_phases, "actual_phases");
+});
+</script>
+</body>
+</html>
diff --git a/dom/events/Event-dispatch-multiple-cancelBubble.html b/dom/events/Event-dispatch-multiple-cancelBubble.html
new file mode 100644
index 00000000000000..2873fd7794b782
--- /dev/null
+++ b/dom/events/Event-dispatch-multiple-cancelBubble.html
@@ -0,0 +1,51 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title>Multiple dispatchEvent() and cancelBubble</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+</head>
+<body>
+<div id=log></div>
+
+<div id="parent" style="display: none">
+    <input id="target" type="hidden" value=""/>
+</div>
+
+<script>
+test(function() {
+    var event_type = "foo";
+    var target = document.getElementById("target");
+    var parent = document.getElementById("parent");
+    var actual_result;
+    var test_event = function(evt) {
+        actual_result.push(evt.currentTarget);
+
+        if (parent == evt.currentTarget) {
+            evt.cancelBubble = true;
+        }
+    };
+
+    var evt = document.createEvent("Event");
+    evt.initEvent(event_type, true, true);
+
+    target.addEventListener(event_type, test_event, false);
+    parent.addEventListener(event_type, test_event, false);
+    document.addEventListener(event_type, test_event, false);
+    window.addEventListener(event_type, test_event, false);
+
+    actual_result = [];
+    target.dispatchEvent(evt);
+    assert_array_equals(actual_result, [target, parent]);
+
+    actual_result = [];
+    parent.dispatchEvent(evt);
+    assert_array_equals(actual_result, [parent]);
+
+    actual_result = [];
+    document.dispatchEvent(evt);
+    assert_array_equals(actual_result, [document, window]);
+});
+</script>
+</body>
+</html>
diff --git a/dom/events/Event-initEvent.html b/dom/events/Event-initEvent.html
index 85abdff2fe7bdb..568232a53c1a64 100644
--- a/dom/events/Event-initEvent.html
+++ b/dom/events/Event-initEvent.html
@@ -85,6 +85,7 @@
   var target = document.createElement("div")
   var called = false
   target.addEventListener("type", function() { called = true }, false)
+  assert_false(e.cancelBubble, "cancelBubble must be false")
   assert_true(target.dispatchEvent(e), "dispatchEvent must return true")
   assert_true(called, "Listener must be called")
 }, "Calling initEvent must unset the stop propagation flag.")
diff --git a/dom/events/Event-propagation.html b/dom/events/Event-propagation.html
index 459d45c1886ca4..33989eb4bf9526 100644
--- a/dom/events/Event-propagation.html
+++ b/dom/events/Event-propagation.html
@@ -38,4 +38,11 @@
 testPropagationFlag(ev, false, "After stopImmediatePropagation()");
 ev.initEvent("foo", true, false);
 testPropagationFlag(ev, true, "Reinitialized after stopImmediatePropagation()");
+
+var ev = document.createEvent("Event");
+ev.initEvent("foo", true, false);
+ev.cancelBubble = true;
+testPropagationFlag(ev, false, "After cancelBubble=true");
+ev.initEvent("foo", true, false);
+testPropagationFlag(ev, true, "Reinitialized after cancelBubble=true");
 </script>
