diff --git a/testing/web-platform/tests/html/browsers/browsing-the-web/remote-context-helper-tests/resources/test-helper.js b/testing/web-platform/tests/html/browsers/browsing-the-web/remote-context-helper-tests/resources/test-helper.js
index 95d516e275280..5f8e07711cbca 100644
--- a/testing/web-platform/tests/html/browsers/browsing-the-web/remote-context-helper-tests/resources/test-helper.js
+++ b/testing/web-platform/tests/html/browsers/browsing-the-web/remote-context-helper-tests/resources/test-helper.js
@@ -46,3 +46,40 @@ async function assertHeaderIsAsExpected(
         return res.headers.get(headerName);
       }, [headerName]), 'header is set');
 }
+
+async function  assertNotRestoredReasonsEquals(
+  remoteContextHelper, blocked, url, src, id, name, reasons, children) {
+  let result = await remoteContextHelper.executeScript(() => {
+    return performance.getEntriesByType('navigation')[0].notRestoredReasons;
+  });
+  assertReasonsStructEquals(result, blocked, url, src, id, name, reasons, children);
+}
+
+function assertReasonsStructEquals(result, blocked, url, src, id, name, reasons, children) {
+  assert_equals(result.blocked, blocked);
+  assert_equals(result.url, url);
+  assert_equals(result.src, src);
+  assert_equals(result.id, id);
+  assert_equals(result.name, name);
+  // Reasons should match.
+  assert_equals(result.reasons.length, reasons.length);
+  reasons.sort();
+  result.reasons.sort();
+  for (let i=0; i<reasons.length; i++) {
+    assert_equals(result.reasons[i], reasons[i]);
+  }
+  // Children should match.
+  assert_equals(result.children.length, children.length);
+  children.sort();
+  result.children.sort();
+  for (let j=0; j<children.length; j++) {
+    assertReasonsStructEquals(result.children[0],
+      children[0].blocked,
+      children[0].url,
+      children[0].src,
+      children[0].id,
+      children[0].name,
+      children[0].reasons,
+      children[0].children);
+  }
+}
\ No newline at end of file
diff --git a/testing/web-platform/tests/performance-timeline/not-restored-reasons/performance-navigation-timing-bfcache.window.js b/testing/web-platform/tests/performance-timeline/not-restored-reasons/performance-navigation-timing-bfcache.window.js
new file mode 100644
index 0000000000000..549e72b30dd63
--- /dev/null
+++ b/testing/web-platform/tests/performance-timeline/not-restored-reasons/performance-navigation-timing-bfcache.window.js
@@ -0,0 +1,31 @@
+// META: title=RemoteContextHelper navigation using BFCache
+// META: script=/common/dispatcher/dispatcher.js
+// META: script=/common/get-host-info.sub.js
+// META: script=/common/utils.js
+// META: script=/resources/testharness.js
+// META: script=/resources/testharnessreport.js
+// META: script=/html/browsers/browsing-the-web/remote-context-helper/resources/remote-context-helper.js
+// META: script=/html/browsers/browsing-the-web/remote-context-helper-tests/resources/test-helper.js
+
+'use strict';
+
+// Ensure that notRestoredReasons is empty for successful BFCache restore.
+promise_test(async t => {
+  const rcHelper = new RemoteContextHelper();
+
+  // Open a window with noopener so that BFCache will work.
+  const rc1 = await rcHelper.addWindow(
+      /*config=*/ null, /*options=*/ {features: 'noopener'});
+
+  // Navigate away.
+  const rc2 = await rc1.navigateToNew();
+
+  // Navigate back.
+  await rc2.historyBack();
+
+  // Verify that no reasons are recorded for successful restore.
+  assert_true(await rc1.executeScript(() => {
+    let reasons = performance.getEntriesByType('navigation')[0].notRestoredReasons;
+    return reasons == null;
+  }));
+});
\ No newline at end of file
diff --git a/testing/web-platform/tests/performance-timeline/not-restored-reasons/performance-navigation-timing-cross-origin-bfcache.window.js b/testing/web-platform/tests/performance-timeline/not-restored-reasons/performance-navigation-timing-cross-origin-bfcache.window.js
new file mode 100644
index 0000000000000..f906b4b0735af
--- /dev/null
+++ b/testing/web-platform/tests/performance-timeline/not-restored-reasons/performance-navigation-timing-cross-origin-bfcache.window.js
@@ -0,0 +1,70 @@
+// META: title=RemoteContextHelper navigation using BFCache
+// META: script=/common/dispatcher/dispatcher.js
+// META: script=/common/get-host-info.sub.js
+// META: script=/common/utils.js
+// META: script=/resources/testharness.js
+// META: script=/resources/testharnessreport.js
+// META: script=/html/browsers/browsing-the-web/remote-context-helper/resources/remote-context-helper.js
+// META: script=/html/browsers/browsing-the-web/remote-context-helper-tests/resources/test-helper.js
+// META: script=/websockets/constants.sub.js
+
+'use strict';
+
+// Ensure that cross-origin subtree's reasons are not exposed to notRestoredReasons.
+promise_test(async t => {
+  const rcHelper = new RemoteContextHelper();
+  // Open a window with noopener so that BFCache will work.
+  const rc1 = await rcHelper.addWindow(
+      /*config=*/ null, /*options=*/ {features: 'noopener'});
+  const rc1_url = await rc1.executeScript(() => {
+    return location.href;
+  });
+  // Add a cross-origin iframe and use BroadcastChannel.
+  const rc1_child = await rc1.addIframe(
+    /*extraConfig=*/ {
+      origin: 'HTTP_REMOTE_ORIGIN',
+      scripts: [],
+      headers: [],
+    },
+    /*attributes=*/ {id: 'test-id'},
+  );
+
+  const domainPort = SCHEME_DOMAIN_PORT;
+  await rc1_child.executeScript((domain) => {
+    var ws = new WebSocket(domain + '/echo');
+  }, [domainPort]);
+
+  const rc1_child_url = await rc1_child.executeScript(() => {
+    return location.href;
+  });
+  // Add a child to the iframe.
+  const rc1_grand_child = await rc1_child.addIframe();
+  const rc1_grand_child_url = await rc1_grand_child.executeScript(() => {
+    return location.href;
+  });
+
+  // Navigate away.
+  const rc2 = await rc1.navigateToNew();
+
+  // Navigate back.
+  await rc2.historyBack();
+
+  // Check the reported reasons.
+  await assertNotRestoredReasonsEquals(
+    rc1,
+    /*blocked=*/false,
+    /*url=*/rc1_url,
+    /*src=*/ "",
+    /*id=*/"",
+    /*name=*/"",
+    /*reasons=*/[],
+    /*children=*/[{
+      "blocked": true,
+      "url": "",
+      "src": "",
+      "id": "",
+      "name": "",
+      "reasons": [],
+      "children": []
+    }]);
+});
\ No newline at end of file
diff --git a/testing/web-platform/tests/performance-timeline/not-restored-reasons/performance-navigation-timing-not-bfcached.window.js b/testing/web-platform/tests/performance-timeline/not-restored-reasons/performance-navigation-timing-not-bfcached.window.js
new file mode 100644
index 0000000000000..ac8af0e88c8a4
--- /dev/null
+++ b/testing/web-platform/tests/performance-timeline/not-restored-reasons/performance-navigation-timing-not-bfcached.window.js
@@ -0,0 +1,44 @@
+// META: title=RemoteContextHelper navigation using BFCache
+// META: script=/common/dispatcher/dispatcher.js
+// META: script=/common/get-host-info.sub.js
+// META: script=/common/utils.js
+// META: script=/resources/testharness.js
+// META: script=/resources/testharnessreport.js
+// META: script=/html/browsers/browsing-the-web/remote-context-helper/resources/remote-context-helper.js
+// META: script=/html/browsers/browsing-the-web/remote-context-helper-tests/resources/test-helper.js
+// META: script=/websockets/constants.sub.js
+
+'use strict';
+
+// Ensure that notRestoredReasons is populated when not restored.
+promise_test(async t => {
+  const rcHelper = new RemoteContextHelper();
+  // Open a window with noopener so that BFCache will work.
+  const rc1 = await rcHelper.addWindow(
+      /*config=*/ null, /*options=*/ {features: 'noopener'});
+
+  const domainPort = SCHEME_DOMAIN_PORT;
+  await rc1.executeScript((domain) => {
+    var ws = new WebSocket(domain + '/echo');
+  }, [domainPort]);
+
+  const rc1_url = await rc1.executeScript(() => {
+    return location.href;
+  });
+
+  // Navigate away.
+  const rc2 = await rc1.navigateToNew();
+
+  // Navigate back.
+  await rc2.historyBack();
+  // Check the reported reasons.
+  await assertNotRestoredReasonsEquals(
+    rc1,
+    /*blocked=*/true,
+    /*url=*/rc1_url,
+    /*src=*/ "",
+    /*id=*/"",
+    /*name=*/"",
+    /*reasons=*/["WebSocket"],
+    /*children=*/[]);
+});
\ No newline at end of file
diff --git a/testing/web-platform/tests/performance-timeline/not-restored-reasons/performance-navigation-timing-same-origin-bfcache.window.js b/testing/web-platform/tests/performance-timeline/not-restored-reasons/performance-navigation-timing-same-origin-bfcache.window.js
new file mode 100644
index 0000000000000..fb5ec50400e5a
--- /dev/null
+++ b/testing/web-platform/tests/performance-timeline/not-restored-reasons/performance-navigation-timing-same-origin-bfcache.window.js
@@ -0,0 +1,73 @@
+// META: title=RemoteContextHelper navigation using BFCache
+// META: script=/common/dispatcher/dispatcher.js
+// META: script=/common/get-host-info.sub.js
+// META: script=/common/utils.js
+// META: script=/resources/testharness.js
+// META: script=/resources/testharnessreport.js
+// META: script=/html/browsers/browsing-the-web/remote-context-helper/resources/remote-context-helper.js
+// META: script=/html/browsers/browsing-the-web/remote-context-helper-tests/resources/test-helper.js
+// META: script=/websockets/constants.sub.js
+
+'use strict';
+
+// Ensure that same-origin subtree's reasons are exposed to notRestoredReasons.
+promise_test(async t => {
+  const rcHelper = new RemoteContextHelper();
+  // Open a window with noopener so that BFCache will work.
+  const rc1 = await rcHelper.addWindow(
+      /*config=*/ null, /*options=*/ {features: 'noopener'});
+  const rc1_url = await rc1.executeScript(() => {
+    return location.href;
+  });
+  // Add a same-origin iframe and use WebSocket.
+  const rc1_child = await rc1.addIframe(/*extra_config=*/{}, /*attributes=*/ {id: 'test-id'});
+
+  const domainPort = SCHEME_DOMAIN_PORT;
+  await rc1_child.executeScript((domain) => {
+    var ws = new WebSocket(domain + '/echo');
+  }, [domainPort]);
+
+  const rc1_child_url = await rc1_child.executeScript(() => {
+    return location.href;
+  });
+  // Add a child to the iframe.
+  const rc1_grand_child = await rc1_child.addIframe();
+  const rc1_grand_child_url = await rc1_grand_child.executeScript(() => {
+    return location.href;
+  });
+
+  // Navigate away.
+  const rc2 = await rc1.navigateToNew();
+
+  // Navigate back.
+  await rc2.historyBack();
+
+  // Check the reported reasons.
+  await assertNotRestoredReasonsEquals(
+    rc1,
+    /*blocked=*/false,
+    /*url=*/rc1_url,
+    /*src=*/ "",
+    /*id=*/"",
+    /*name=*/"",
+    /*reasons=*/[],
+    /*children=*/[{
+      "blocked": true,
+      "url": rc1_child_url,
+      "src": rc1_child_url,
+      "id": "test-id",
+      "name": "",
+      "reasons": ["WebSocket"],
+      "children": [
+        {
+        "blocked": false,
+        "url": rc1_grand_child_url,
+        "src": rc1_grand_child_url,
+        "id": "",
+        "name": "",
+        "reasons": [],
+        "children": []
+        }
+      ]
+    }]);
+});
\ No newline at end of file