diff --git a/html/browsers/history/the-location-interface/location-ancestororigins-involved.window.js b/html/browsers/history/the-location-interface/location-ancestororigins-involved.window.js
new file mode 100644
index 00000000000000..1a100edac3f968
--- /dev/null
+++ b/html/browsers/history/the-location-interface/location-ancestororigins-involved.window.js
@@ -0,0 +1,180 @@
+// META: script=/common/get-host-info.sub.js
+
+function checkSupported() {
+  assert_implements('ancestorOrigins' in location, 'location.ancestorOrigins should be supported');
+}
+
+const embedPath = new URL("resources/ancestororigins-embed.py", location.href).pathname,
+      info = get_host_info(),
+      localOrigin = info.HTTP_ORIGIN,
+      localEmbed = localOrigin + embedPath,
+      remoteOrigin = info.HTTP_REMOTE_ORIGIN,
+      remoteEmbed = remoteOrigin + embedPath,
+      remoteOrigin2 = info.HTTP_REMOTE_ORIGIN_WITH_DIFFERENT_PORT,
+      remoteEmbed2 = remoteOrigin2 + embedPath;
+let id = 0;
+
+async_test(t => {
+  checkSupported();
+  const iframe = document.createElement("iframe"),
+        localId = ++id;
+  iframe.sandbox = "allow-scripts";
+  iframe.src = localEmbed + "?iframe=|" + encodeURIComponent(remoteEmbed) + "?id=" + localId;
+  document.body.appendChild(iframe);
+  t.add_cleanup(() => iframe.remove());
+
+  self.addEventListener("message", t.step_func(e => {
+    if(e.data.id === localId) {
+      assert_array_equals(e.data.output, ["null", localOrigin]);
+      t.done();
+    }
+  }));
+}, "Ensure sandboxed iframes show up as null");
+
+// The following code ends up generating multiple tests each with multiple nested <iframe>s. The
+// variables in the array below seed various scenarios, described by "desc". The capital letters
+// describe the <iframe>s in play. When the same letter is used at different nesting levels that
+// means it is same-origin. Some defaulting is used to avoid too much duplication.
+[
+  {
+    outerPolicy: true,
+    desc: "A uses no-referrer -> B -> A",
+    results: [remoteOrigin, "null"]
+  },
+  {
+    outerPolicy: true,
+    innerEmbed: remoteEmbed2,
+    desc: "A uses no-referrer -> B -> C",
+    results: [remoteOrigin, "null"]
+  },
+  {
+    innerPolicy: true,
+    desc: "A -> B uses no-referrer -> A",
+    results: ["null", localOrigin]
+  },
+  {
+    innerPolicy: true,
+    innerEmbed: remoteEmbed2,
+    desc: "A -> B uses no-referrer -> C",
+    results: ["null", localOrigin]
+  },
+  {
+    innerPolicy: true,
+    outerEmbed: localEmbed,
+    innerEmbed: remoteEmbed,
+    desc: "A -> A uses no-referrer -> C",
+    results: ["null", "null"],
+    intermediateResults: [localOrigin]
+  },
+  {
+    innerPolicy: true,
+    outerEmbed: localEmbed,
+    desc: "A -> A uses no-referrer -> A",
+    results: ["null", "null"],
+    intermediateResults: [localOrigin]
+  }
+].forEach(val => {
+  async_test(t => {
+    checkSupported();
+    if(!val.intermediateResults) {
+      val.intermediateResults = [val.results[1]];
+    }
+    if(!val.outerEmbed) {
+      val.outerEmbed = remoteEmbed;
+    }
+    if(!val.innerEmbed) {
+      val.innerEmbed = localEmbed;
+    }
+
+    const iframe = document.createElement("iframe"),
+          innerId = ++id,
+          innermostId = ++id;
+    if(val.outerPolicy) {
+      iframe.referrerPolicy = "no-referrer";
+    }
+    let innerPolicy = "";
+    if(val.innerPolicy) {
+      innerPolicy = "no-referrer";
+    }
+    iframe.src = val.outerEmbed + "?id=" + innerId + "&iframe=" + innerPolicy + "|" + val.innerEmbed + "?id=" + innermostId;
+    document.body.appendChild(iframe);
+    t.add_cleanup(() => iframe.remove());
+
+    let almostDone = false;
+    function localDone () {
+      if(almostDone) {
+        t.done();
+      }
+      almostDone = true;
+    }
+
+    self.addEventListener("message", t.step_func(e => {
+      if(e.data.id === innerId) {
+        assert_array_equals(e.data.output, val.intermediateResults);
+        localDone();
+      }
+      else if(e.data.id === innermostId) {
+        assert_array_equals(e.data.output, val.results);
+        localDone();
+      }
+    }));
+  }, val.desc);
+});
+
+[
+  {
+    desc: "A -> B -> B uses no-referrer -> A",
+    innerinnerEmbed: localEmbed
+  },
+  {
+    desc: "A -> B -> B uses no-referrer -> B",
+    innerinnerEmbed: remoteEmbed
+  },
+  {
+    desc: "A -> B -> B uses no-referrer -> C",
+    innerinnerEmbed: remoteEmbed2
+  }
+].forEach(val => {
+  async_test(t => {
+    checkSupported();
+    const iframe = document.createElement("iframe"),
+          localId = ++id;
+    iframe.src = remoteEmbed + "?iframe=|" + remoteEmbed + "?iframe=no-referrer%257C" + val.innerinnerEmbed + "?id=" + localId;
+    document.body.appendChild(iframe);
+    t.add_cleanup(() => iframe.remove());
+
+    self.addEventListener("message", t.step_func(e => {
+      if(e.data.id === localId) {
+        assert_array_equals(e.data.output, ["null", "null", localOrigin]);
+        t.done();
+      }
+    }));
+  }, val.desc);
+});
+
+// rel=noreferrer sets https://html.spec.whatwg.org/#document-state-request-referrer-policy
+// but does not affect https://html.spec.whatwg.org/#policy-container-referrer-policy
+async_test(t => {
+  checkSupported();
+  const iframe = document.createElement("iframe"),
+        localId = ++id;
+  iframe.src = '/common/blank.html';
+  document.body.appendChild(iframe);
+  t.add_cleanup(() => iframe.remove());
+
+  iframe.addEventListener('load', () => {
+    const a = document.createElement("a");
+    a.rel = "noreferrer";
+    a.href = localEmbed + "?id=" + localId;
+    a.textContent = 'click here';
+    iframe.contentDocument.body.appendChild(a);
+
+    self.addEventListener("message", t.step_func(e => {
+      if(e.data.id === localId) {
+        assert_array_equals(e.data.output, [localOrigin]);
+        t.done();
+      }
+    }));
+    a.click();
+  }, {once: true});
+}, "rel=noreferrer should not affect ancestorOrigins");
diff --git a/html/browsers/history/the-location-interface/location-ancestororigins.window.js b/html/browsers/history/the-location-interface/location-ancestororigins.window.js
new file mode 100644
index 00000000000000..5742c6a4c25354
--- /dev/null
+++ b/html/browsers/history/the-location-interface/location-ancestororigins.window.js
@@ -0,0 +1,78 @@
+function checkSupported() {
+  assert_implements('ancestorOrigins' in location, 'location.ancestorOrigins should be supported');
+}
+
+test(() => {
+  checkSupported();
+  assert_equals(location.ancestorOrigins.length, 0)
+}, "location.ancestorOrigins basic check");
+
+async_test(t => {
+  checkSupported();
+  const frame = document.createElement("iframe"),
+        rp = document.createElement("meta");
+  frame.onload = t.step_func_done(() => {
+    const ancestorOrigins = frame.contentWindow.location.ancestorOrigins;
+    assert_equals(ancestorOrigins[0], self.origin);
+    assert_equals(ancestorOrigins.length, 1);
+
+    rp.name = "referrer";
+    rp.content = "no-referrer";
+    document.head.appendChild(rp);
+    assert_equals(self[0].location.ancestorOrigins, ancestorOrigins);
+    assert_equals(ancestorOrigins[0], self.origin);
+    assert_equals(ancestorOrigins.length, 1);
+    rp.remove();
+
+    frame.referrerPolicy = "no-referrer";
+    assert_equals(self[0].location.ancestorOrigins, ancestorOrigins);
+    assert_equals(ancestorOrigins[0], self.origin);
+    assert_equals(ancestorOrigins.length, 1);
+
+    frame.remove();
+  })
+  frame.src = "/common/blank.html";
+  document.body.appendChild(frame);
+}, "location.ancestorOrigins cannot be masked by a dynamic referrer policy");
+
+async_test(t => {
+  checkSupported();
+  const frame = document.createElement("iframe");
+  frame.onload = t.step_func_done(() => {
+    const ancestorOrigins = frame.contentWindow.location.ancestorOrigins;
+    assert_equals(ancestorOrigins[0], "null");
+    assert_equals(ancestorOrigins.length, 1);
+    frame.remove();
+  })
+  frame.src = "/common/blank.html";
+  frame.referrerPolicy = "no-referrer";
+  document.body.appendChild(frame);
+}, "location.ancestorOrigins can be masked by a predetermined referrer policy");
+
+async_test(t => {
+  checkSupported();
+  const frame = document.createElement("iframe");
+  t.add_cleanup(() => frame.remove());
+  frame.src = new URL("resources/ancestororigins-embed.py?id=123&iframe=|./ancestororigins-embed.py%3Fid=1234", location.href.replace("://", "://天気の良い日.")).href;
+  document.body.appendChild(frame);
+
+  let almostDone = false;
+  function localDone() {
+    if(almostDone) {
+      t.done();
+    }
+    almostDone = true;
+  }
+
+  self.onmessage = t.step_func(e => {
+    if(e.data.id === 123) {
+      assert_array_equals(e.data.output, [location.origin]);
+      localDone();
+    } else if(e.data.id === 1234) {
+      assert_array_equals(e.data.output, [location.origin.replace("://", "://xn--n8j6ds53lwwkrqhv28a."), location.origin]);
+      localDone();
+    } else {
+      assert_unreached();
+    }
+  });
+}, "location.ancestorOrigins and IDNA");
diff --git a/html/browsers/history/the-location-interface/resources/ancestororigins-embed.py b/html/browsers/history/the-location-interface/resources/ancestororigins-embed.py
new file mode 100644
index 00000000000000..e16e5cbd61aa04
--- /dev/null
+++ b/html/browsers/history/the-location-interface/resources/ancestororigins-embed.py
@@ -0,0 +1,23 @@
+def main(request, response):
+    headers = [("Content-Type", "text/html; charset=utf-8")]
+    body = "<!doctype html>"
+
+    if b"iframe" in request.GET:
+        frame = request.GET.first(b"iframe").split(b"|")
+        frameReferrer = frame[0].decode("utf-8")
+        frameURL = frame[1].decode("utf-8")
+        if frameReferrer != "":
+            frameReferrer = " referrerpolicy=" + frameReferrer
+
+        body = body + ("<iframe src=\"%s\"%s></iframe>" % (frameURL, frameReferrer)) + "\n"
+
+    if b"id" in request.GET:
+        body = body + """<script>
+let output = [...self.location.ancestorOrigins];
+top.postMessage({ id: %s, output }, "*");
+</script>
+""" % request.GET.first(b"id").decode("utf-8")
+
+    if body == "<!doctype html>":
+        return "Please specify either or both the 'iframe' and 'id' GET parameters."
+    return (headers, body)