diff --git a/testing/web-platform/meta/MANIFEST.json b/testing/web-platform/meta/MANIFEST.json
index 4dbe21e0c065..e5b47e0c6392 100644
--- a/testing/web-platform/meta/MANIFEST.json
+++ b/testing/web-platform/meta/MANIFEST.json
@@ -583054,7 +583054,7 @@
    "testharness"
   ],
   "service-workers/service-worker/activation.https.html": [
-   "cdd7cd200ff4ec3df61c257305953b3a1f369ab8",
+   "b7a9ca969b4122f1b9adc973c60044a6ab2a2a95",
    "testharness"
   ],
   "service-workers/service-worker/active.https.html": [
@@ -583150,7 +583150,7 @@
    "testharness"
   ],
   "service-workers/service-worker/detached-context.https.html": [
-   "c7645323ba0753f35beaef90836631ca16f64d3a",
+   "a4e96edc51927eb29873b0c97a7232f71ae43378",
    "testharness"
   ],
   "service-workers/service-worker/extendable-event-async-waituntil.https.html": [
@@ -584534,7 +584534,7 @@
    "support"
   ],
   "service-workers/service-worker/resources/test-helpers.sub.js": [
-   "55acaa1edd73a39a834e1a1ee0952f47a03e3c78",
+   "5567e4c45d07a90c4fc7fefa3475e564f0d46e5a",
    "support"
   ],
   "service-workers/service-worker/resources/testharness-helpers.js": [
diff --git a/testing/web-platform/tests/service-workers/service-worker/activation.https.html b/testing/web-platform/tests/service-workers/service-worker/activation.https.html
index 82138dda466e..48aefd4a7af6 100644
--- a/testing/web-platform/tests/service-workers/service-worker/activation.https.html
+++ b/testing/web-platform/tests/service-workers/service-worker/activation.https.html
@@ -6,24 +6,6 @@
 <script src="resources/test-helpers.sub.js"></script>
 <body>
 <script>
-// Registers, waits for activation, then unregisters on a dummy scope.
-//
-// This helper can be used in tests that assert that activation doesn't happen.
-// It would not be sufficient to check the .waiting/.active properties once,
-// since activation could be scheduled and just hasn't happened yet. Since this
-// helper shows that activation of another registration completed, we can be
-// sure that activation really will not happen.
-function wait_for_activation_on_dummy_scope(t) {
-  var dummy_scope = 'resources/there/is/no/there/there';
-  var registration;
-  return navigator.serviceWorker.register('resources/empty-worker.js',
-      { scope: dummy_scope })
-    .then(r => {
-        registration = r;
-        return wait_for_state(t, registration.installing, 'activated');
-      })
-    .then(() => registration.unregister());
-}
 // Returns {registration, iframe}, where |registration| has an active and
 // waiting worker. The active worker controls |iframe| and has an inflight
 // message event that can be finished by calling
diff --git a/testing/web-platform/tests/service-workers/service-worker/detached-context.https.html b/testing/web-platform/tests/service-workers/service-worker/detached-context.https.html
index d345982343f0..e70de4d70b61 100644
--- a/testing/web-platform/tests/service-workers/service-worker/detached-context.https.html
+++ b/testing/web-platform/tests/service-workers/service-worker/detached-context.https.html
@@ -16,6 +16,7 @@ promise_test(t => {
     const scope_for_main = 'resources/' + scope_for_iframe;
     const script = 'resources/empty-worker.js';
     let frame;
+    let resolvedCount = 0;
 
     return service_worker_unregister(t, scope_for_main)
       .then(() => {
@@ -41,9 +42,23 @@ promise_test(t => {
           assert_equals(r.active.state, 'activated');
           assert_equals(r.scope, normalizeURL(scope_for_main));
           r.onupdatefound = () => { /* empty */ };
-          return Promise.all([
-              promise_rejects(t, 'InvalidStateError', r.unregister()),
-              promise_rejects(t, 'InvalidStateError', r.update())]);
+
+          // We want to verify that unregister() and update() do not
+          // resolve on a detached registration.  We can't check for
+          // an explicit rejection, though, because not all browsers
+          // fire rejection callbacks on detached promises.  Instead
+          // we wait for a dummy scope to install, activate, and
+          // unregister before declaring that the promises did not
+          // resolve.
+          r.unregister().then(() => resolvedCount += 1,
+                              () => {});
+          r.update().then(() => resolvedCount += 1,
+                          () => {});
+          return wait_for_activation_on_dummy_scope(t);
+        })
+      .then(() => {
+          assert_equals(resolvedCount, 0,
+                        'methods called on a detached registration should not resolve');
         })
   }, 'accessing a ServiceWorkerRegistration from a removed iframe');
 
diff --git a/testing/web-platform/tests/service-workers/service-worker/resources/test-helpers.sub.js b/testing/web-platform/tests/service-workers/service-worker/resources/test-helpers.sub.js
index 38ec4ae9674f..0dc1d762c911 100644
--- a/testing/web-platform/tests/service-workers/service-worker/resources/test-helpers.sub.js
+++ b/testing/web-platform/tests/service-workers/service-worker/resources/test-helpers.sub.js
@@ -257,3 +257,17 @@ function with_sandboxed_iframe(url, sandbox) {
       document.body.appendChild(frame);
     });
 }
+
+// Registers, waits for activation, then unregisters on a dummy scope.
+//
+// This can be used to wait for a period of time needed to register,
+// activate, and then unregister a service worker.  When checking that
+// certain behavior does *NOT* happen, this is preferable to using an
+// arbitrary setTimeout() delay.
+async function wait_for_activation_on_dummy_scope(t) {
+  const script = 'resources/empty-worker.js';
+  const scope = 'resources/there/is/no/there/there?' + Date.now();
+  let registration = await navigator.serviceWorker.register(script, { scope });
+  await wait_for_state(t, registration.installing, 'activated');
+  await registration.unregister();
+}
