diff --git a/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/abort-while-navigating.window.js b/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/abort-while-navigating.window.js
new file mode 100644
index 00000000000000..c0c6ac15b16ccf
--- /dev/null
+++ b/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/abort-while-navigating.window.js
@@ -0,0 +1,171 @@
+async_test(t => {
+  const frame = document.body.appendChild(document.createElement("iframe"));
+  t.add_cleanup(() => frame.remove());
+  frame.src = "/common/blank.html";
+  frame.onload = t.step_func(() => {
+    frame.onload = null;
+    const client = new frame.contentWindow.XMLHttpRequest();
+    client.open("GET", "/common/blank.html");
+    // The abort event handler is called synchronously in Chrome but
+    // asynchronously in Firefox. See https://crbug.com/879620.
+    client.onabort = t.step_func_done();
+    client.send();
+    frame.contentWindow.location.href = new URL("resources/dummy.html", document.URL);
+    frame.contentDocument.open();
+  });
+}, "document.open() aborts documents that are navigating through Location (XMLHttpRequest)");
+
+async_test(t => {
+  const frame = document.body.appendChild(document.createElement("iframe"));
+  t.add_cleanup(() => frame.remove());
+  frame.src = "/common/blank.html";
+  frame.onload = t.step_func(() => {
+    frame.onload = null;
+    let happened = false;
+    frame.contentWindow.fetch("/common/blank.html").then(
+      t.unreached_func("Fetch should have been aborted"),
+      t.step_func_done(() => {
+        assert_true(happened);
+      }));
+    frame.contentWindow.location.href = new URL("resources/dummy.html", document.URL);
+    frame.contentDocument.open();
+    happened = true;
+  });
+}, "document.open() aborts documents that are navigating through Location (fetch())");
+
+async_test(t => {
+  const frame = document.body.appendChild(document.createElement("iframe"));
+  t.add_cleanup(() => frame.remove());
+  frame.src = "/common/blank.html";
+  frame.onload = t.step_func(() => {
+    frame.onload = null;
+    let happened = false;
+    const img = frame.contentDocument.createElement("img");
+    img.src = new URL("resources/slow-png.py", document.URL);
+    img.onload = t.unreached_func("Image loading should have errored");
+    // The image fetch starts in a microtask, so let's be sure to test after
+    // the fetch has started.
+    t.step_timeout(() => {
+      frame.contentWindow.location.href = new URL("resources/dummy.html", document.URL);
+      frame.contentDocument.open();
+      happened = true;
+    });
+    // If 3 seconds have passed and the image has still not loaded, we consider
+    // it aborted. slow-png.py only sleeps for 2 wallclock seconds.
+    t.step_timeout(t.step_func_done(() => {
+      assert_true(happened);
+    }), 3000);
+  });
+}, "document.open() aborts documents that are navigating through Location (image loading)");
+
+async_test(t => {
+  const div = document.body.appendChild(document.createElement("div"));
+  t.add_cleanup(() => div.remove());
+  div.innerHTML = "<iframe src='resources/slow.py'></iframe>";
+  const frame = div.childNodes[0];
+  const client = new frame.contentWindow.XMLHttpRequest();
+  client.open("GET", "/common/blank.html");
+  client.onabort = t.step_func_done();
+  client.send();
+  frame.contentDocument.open();
+}, "document.open() aborts documents that are navigating through iframe loading (XMLHttpRequest)");
+
+async_test(t => {
+  const div = document.body.appendChild(document.createElement("div"));
+  t.add_cleanup(() => div.remove());
+  div.innerHTML = "<iframe src='resources/slow.py'></iframe>";
+  const frame = div.childNodes[0];
+  frame.contentWindow.fetch("/common/blank.html").then(
+    t.unreached_func("Fetch should have been aborted"),
+    t.step_func_done());
+  frame.contentDocument.open();
+}, "document.open() aborts documents that are navigating through iframe loading (fetch())");
+
+// We use resources/slow.py here, to prevent the situation where when
+// document.open() is called the initial document has already become inactive.
+async_test(t => {
+  const div = document.body.appendChild(document.createElement("div"));
+  t.add_cleanup(() => div.remove());
+  div.innerHTML = "<iframe src='resources/slow.py'></iframe>";
+  const frame = div.childNodes[0];
+  let happened = false;
+  const img = frame.contentDocument.createElement("img");
+  img.src = new URL("resources/slow-png.py", document.URL);
+  img.onload = t.unreached_func("Image loading should have errored");
+  // The image fetch starts in a microtask, so let's be sure to test after
+  // the fetch has started.
+  t.step_timeout(() => {
+    frame.contentDocument.open();
+    happened = true;
+  });
+  // If 3 seconds have passed and the image has still not loaded, we consider
+  // it aborted. slow-png.py only sleeps for 2 wallclock seconds.
+  t.step_timeout(t.step_func_done(() => {
+    assert_true(happened);
+  }), 3000);
+}, "document.open() aborts documents that are navigating through iframe loading (image loading)");
+
+async_test(t => {
+  const frame = document.body.appendChild(document.createElement("iframe"));
+  t.add_cleanup(() => frame.remove());
+  frame.src = "/common/blank.html";
+  frame.onload = t.step_func(() => {
+    frame.onload = null;
+    const link = frame.contentDocument.body.appendChild(frame.contentDocument.createElement("a"));
+    link.href = new URL("resources/dummy.html", document.URL);
+
+    const client = new frame.contentWindow.XMLHttpRequest();
+    client.open("GET", "/common/blank.html");
+    client.onabort = t.step_func_done();
+    client.send();
+
+    link.click();
+    frame.contentDocument.open();
+  });
+}, "document.open() aborts documents that are queued for navigation through .click() (XMLHttpRequest)");
+
+async_test(t => {
+  const frame = document.body.appendChild(document.createElement("iframe"));
+  t.add_cleanup(() => frame.remove());
+  frame.src = "/common/blank.html";
+  frame.onload = t.step_func(() => {
+    frame.onload = null;
+    const link = frame.contentDocument.body.appendChild(frame.contentDocument.createElement("a"));
+    link.href = new URL("resources/dummy.html", document.URL);
+
+    frame.contentWindow.fetch("/common/blank.html").then(
+      t.unreached_func("Fetch should have been aborted"),
+      t.step_func_done());
+
+    link.click();
+    frame.contentDocument.open();
+  });
+}, "document.open() aborts documents that are queued for navigation through .click() (fetch())");
+
+async_test(t => {
+  const frame = document.body.appendChild(document.createElement("iframe"));
+  t.add_cleanup(() => frame.remove());
+  frame.src = "/common/blank.html";
+  frame.onload = t.step_func(() => {
+    frame.onload = null;
+    const link = frame.contentDocument.body.appendChild(frame.contentDocument.createElement("a"));
+    link.href = new URL("resources/dummy.html", document.URL);
+
+    let happened = false;
+    const img = frame.contentDocument.createElement("img");
+    img.src = new URL("resources/slow-png.py", document.URL);
+    img.onload = t.unreached_func("Image loading should have errored");
+    // The image fetch starts in a microtask, so let's be sure to test after
+    // the fetch has started.
+    t.step_timeout(() => {
+      link.click();
+      frame.contentDocument.open();
+      happened = true;
+    });
+    // If 3 seconds have passed and the image has still not loaded, we consider
+    // it aborted. slow-png.py only sleeps for 2 wallclock seconds.
+    t.step_timeout(t.step_func_done(() => {
+      assert_true(happened);
+    }), 3000);
+  });
+}, "document.open() aborts documents that are queued for navigation through .click() (image loading)");
diff --git a/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/abort.sub.window.js b/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/abort.sub.window.js
new file mode 100644
index 00000000000000..885468902ec39b
--- /dev/null
+++ b/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/abort.sub.window.js
@@ -0,0 +1,104 @@
+async_test(t => {
+  const frame = document.body.appendChild(document.createElement("iframe"));
+  t.add_cleanup(() => frame.remove());
+  frame.src = "/common/blank.html";
+  frame.onload = t.step_func(() => {
+    frame.onload = null;
+    let happened = false;
+    const client = new frame.contentWindow.XMLHttpRequest();
+    client.open("GET", "/common/blank.html");
+    client.onload = t.step_func_done(e => {
+      assert_true(happened);
+    });
+    client.onerror = t.unreached_func("XMLHttpRequest should have succeeded");
+    client.onabort = t.unreached_func("XMLHttpRequest should have succeeded");
+    client.ontimeout = t.unreached_func("XMLHttpRequest should have succeeded");
+    client.send();
+    frame.contentDocument.open();
+    happened = true;
+  });
+}, "document.open() does not abort documents that are not navigating (XMLHttpRequest)");
+
+async_test(t => {
+  const frame = document.body.appendChild(document.createElement("iframe"));
+  t.add_cleanup(() => frame.remove());
+  frame.src = "/common/blank.html";
+  frame.onload = t.step_func(() => {
+    frame.onload = null;
+    let happened = false;
+    frame.contentWindow.fetch("/common/blank.html").then(
+      t.step_func_done(() => {
+        assert_true(happened);
+      }),
+      t.unreached_func("Fetch should have succeeded")
+    );
+    frame.contentDocument.open();
+    happened = true;
+  });
+}, "document.open() does not abort documents that are not navigating (fetch())");
+
+async_test(t => {
+  const frame = document.body.appendChild(document.createElement("iframe"));
+  t.add_cleanup(() => frame.remove());
+  frame.src = "/common/blank.html";
+  frame.onload = t.step_func(() => {
+    frame.onload = null;
+    let happened = false;
+    const img = frame.contentDocument.createElement("img");
+    img.src = new URL("resources/slow-png.py", document.URL);
+    img.onload = t.step_func_done(() => {
+      assert_true(happened);
+    });
+    img.onerror = t.unreached_func("Image loading should not have errored");
+    // The image fetch starts in a microtask, so let's be sure to test after
+    // the fetch has started.
+    t.step_timeout(() => {
+      frame.contentDocument.open();
+      happened = true;
+    });
+  });
+}, "document.open() does not abort documents that are not navigating (image loading)");
+
+async_test(t => {
+  const __SERVER__NAME = "{{host}}";
+  const __PORT = {{ports[ws][0]}};
+  const frame = document.body.appendChild(document.createElement("iframe"));
+  t.add_cleanup(() => frame.remove());
+  frame.src = "/common/blank.html";
+  frame.onload = t.step_func(() => {
+    frame.onload = null;
+    let happened = false;
+    const ws = new frame.contentWindow.WebSocket(`ws://${__SERVER__NAME}:${__PORT}/echo`);
+    ws.onopen = t.step_func_done(() => {
+      assert_true(happened);
+    });
+    ws.onclose = t.unreached_func("WebSocket fetch should have succeeded");
+    ws.onerror = t.unreached_func("WebSocket should have no error");
+    frame.contentDocument.open();
+    happened = true;
+  });
+}, "document.open() does not abort documents that are not navigating (establish a WebSocket connection)");
+
+// An already established WebSocket connection shouldn't be terminated during
+// an "abort a document" anyway. Test just for completeness.
+async_test(t => {
+  const __SERVER__NAME = "{{host}}";
+  const __PORT = {{ports[ws][0]}};
+  const frame = document.body.appendChild(document.createElement("iframe"));
+  t.add_cleanup(() => frame.remove());
+  frame.src = "/common/blank.html";
+  frame.onload = t.step_func(() => {
+    frame.onload = null;
+    let happened = false;
+    const ws = new frame.contentWindow.WebSocket(`ws://${__SERVER__NAME}:${__PORT}/echo`);
+    ws.onopen = t.step_func(() => {
+      t.step_timeout(t.step_func_done(() => {
+        assert_true(happened);
+      }), 100);
+      frame.contentDocument.open();
+      happened = true;
+    });
+    ws.onclose = t.unreached_func("WebSocket should not be closed");
+    ws.onerror = t.unreached_func("WebSocket should have no error");
+  });
+}, "document.open() does not abort documents that are not navigating (already established WebSocket connection)");
diff --git a/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/resources/slow-png.py b/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/resources/slow-png.py
new file mode 100644
index 00000000000000..5fa2fd9a9d850a
--- /dev/null
+++ b/html/webappapis/dynamic-markup-insertion/opening-the-input-stream/resources/slow-png.py
@@ -0,0 +1,8 @@
+from base64 import decodestring
+import time
+
+png_response = decodestring('iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAAAAAA6fptVAAAACklEQVR4nGNiAAAABgADNjd8qAAAAABJRU5ErkJggg==')
+
+def main(request, response):
+    time.sleep(2)
+    return 200, [], png_response