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diff --git a/testing/web-platform/tests/compute-pressure/compute_pressure_detached_iframe.https.html b/testing/web-platform/tests/compute-pressure/compute_pressure_detached_iframe.https.html
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index 0000000000..6123521248
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+++ b/testing/web-platform/tests/compute-pressure/compute_pressure_detached_iframe.https.html
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+<!doctype html>
+<meta charset="utf-8">
+<title>PressureObserver on DOMWindow of detached iframe</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/test-only-api.js"></script>
+<script src="resources/pressure-helpers.js"></script>
+<body>
+<script>
+'use strict';
+
+test(() => {
+  const iframe = document.createElement('iframe');
+  document.body.appendChild(iframe);
+  const frame_window = iframe.contentWindow;
+
+  iframe.remove();
+  assert_equals(undefined, frame_window.PressureObserver);
+}, 'PressureObserver constructor does not exist in detached iframes');
+
+promise_test(async t => {
+  const iframe = document.createElement('iframe');
+  document.body.appendChild(iframe);
+  const frame_window = iframe.contentWindow;
+
+  const observer = new frame_window.PressureObserver(() => {});
+  const iframe_DOMException = frame_window.DOMException;
+
+  iframe.remove();
+
+  // Calling observe() from a detached iframe should fail but not crash.
+  await promise_rejects_dom(t, 'NotSupportedError', iframe_DOMException,
+                            observer.observe('cpu'));
+}, 'PressureObserver.observe() on detached frame rejects');
+
+promise_test(async t => {
+  const iframe = document.createElement('iframe');
+  document.body.appendChild(iframe);
+  const frame_window = iframe.contentWindow;
+
+  const observer = new frame_window.PressureObserver(() => {});
+
+  await observer.observe('cpu');
+
+  iframe.remove();
+
+  // Calling disconnect() from a detached iframe should not crash.
+  observer.disconnect();
+}, 'PressureObserver.disconnect() on detached frame returns');
+
+pressure_test(async (t, mockPressureService) => {
+  const iframe = document.createElement('iframe');
+  document.body.appendChild(iframe);
+  const frame_window = iframe.contentWindow;
+
+  const observer = new frame_window.PressureObserver(() => {});
+  const iframe_DOMException = frame_window.DOMException;
+
+  // await is intentionally not used here. We want to remove the iframe while
+  // the returned Promise settles.
+  observer.observe('cpu');
+  iframe.remove();
+
+  // Establish an observer and wait for changes in the main frame. This should
+  // keep the test running long enough to catch any crash from the observe()
+  // call in the removed iframe's PressureObserver.
+  const changes = await new Promise((resolve, reject) => {
+    const observer = new PressureObserver(resolve);
+    t.add_cleanup(() => observer.disconnect());
+    observer.observe('cpu').catch(reject);
+    mockPressureService.setPressureUpdate('cpu', 'critical');
+    mockPressureService.startPlatformCollector(/*sampleInterval=*/ 200);
+  });
+  assert_equals(changes[0].state, 'critical');
+}, 'Detaching frame while PressureObserver.observe() settles');
+
+pressure_test(async (t, mockPressureService) => {
+  const iframe = document.createElement('iframe');
+  document.body.appendChild(iframe);
+  const frame_window = iframe.contentWindow;
+  const observer = new frame_window.PressureObserver(() => {
+    assert_unreached('The observer callback should not be called');
+  });
+
+  await observer.observe('cpu');
+  mockPressureService.setPressureUpdate('cpu', 'critical');
+  mockPressureService.startPlatformCollector(/*sampleInterval=*/ 200);
+
+  iframe.remove();
+
+  return new Promise(resolve => t.step_timeout(resolve, 1000));
+}, 'PressureObserver on detached frame returns with no callback');
+
+</script>
+</body>