diff --git a/testing/web-platform/tests/navigation-api/navigate-event/intercept-and-navigate.html b/testing/web-platform/tests/navigation-api/navigate-event/intercept-and-navigate.html
index dfbb67b6b6b1c..e689dd6974e47 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/intercept-and-navigate.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/intercept-and-navigate.html
@@ -3,6 +3,9 @@
 <script src="/resources/testharnessreport.js"></script>
 <script>
 promise_test(async t => {
+  let start_length = navigation.entries().length;
+  let start_index = navigation.currentEntry.index;
+
   // Wait for after the load event so that the navigation doesn't get converted
   // into a replace navigation.
   await new Promise(r => window.onload = () => t.step_timeout(r, 0));
@@ -12,8 +15,8 @@
   navigation.oncurrententrychange = e => {
     if (e.navigationType == "traverse") {
       assert_equals(location.hash, "");
-      assert_equals(navigation.currentEntry.index, 0);
-      assert_equals(navigation.entries().length, 2);
+      assert_equals(navigation.currentEntry.index, start_index);
+      assert_equals(navigation.entries().length, start_length + 1);
       navigation.navigate("#2");
     }
   };
@@ -21,7 +24,7 @@
   await back_result.committed;
   assert_equals(location.hash, "#2");
   await promise_rejects_dom(t, "AbortError", back_result.finished);
-  assert_equals(navigation.currentEntry.index, 1);
-  assert_equals(navigation.entries().length, 2);
+  assert_equals(navigation.currentEntry.index, start_index + 1);
+  assert_equals(navigation.entries().length, start_length + 1);
 }, "Using intercept() then navigate() in the ensuing currententrychange should abort the finished promise (but not the committed promise)");
 </script>
diff --git a/testing/web-platform/tests/navigation-api/navigate-event/intercept-navigation-back.html b/testing/web-platform/tests/navigation-api/navigate-event/intercept-navigation-back.html
index 8babf2bcdcc5b..7c7b80d510090 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/intercept-navigation-back.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/intercept-navigation-back.html
@@ -3,6 +3,9 @@
 <script src="/resources/testharnessreport.js"></script>
 <script>
 async_test(t => {
+  let start_length = navigation.entries().length;
+  let start_index = navigation.currentEntry.index;
+
   // Wait for after the load event so that the navigation doesn't get converted
   // into a replace navigation.
   window.onload = () => t.step_timeout(() => {
@@ -10,8 +13,8 @@
       assert_true(navigation.canGoBack);
       navigation.onnavigate = t.step_func(e => e.intercept());
       navigation.back().committed.then(t.step_func_done(() => {
-        assert_equals(navigation.entries().length, 2);
-        assert_equals(navigation.currentEntry, navigation.entries()[0]);
+        assert_equals(navigation.entries().length, start_length + 1);
+        assert_equals(navigation.currentEntry, navigation.entries()[start_index]);
       }));
     });
   }, 0);
diff --git a/testing/web-platform/tests/navigation-api/navigate-event/intercept-same-document-history-back.html b/testing/web-platform/tests/navigation-api/navigate-event/intercept-same-document-history-back.html
index 6faabe1964651..6f57d95b1afd9 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/intercept-same-document-history-back.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/intercept-same-document-history-back.html
@@ -3,6 +3,9 @@
 <script src="/resources/testharnessreport.js"></script>
 <script>
 async_test(t => {
+  let start_length = navigation.entries().length;
+  let start_index = navigation.currentEntry.index;
+
   // Wait for after the load event so that the navigation doesn't get converted
   // into a replace navigation.
   window.onload = () => t.step_timeout(() => {
@@ -15,13 +18,13 @@
     navigation.onnavigatesuccess = t.step_func(e => {
       onnavigatesuccess_calls++;
       if (onnavigatesuccess_calls == 3) {
-        assert_equals(navigation.entries().length, 3);
-        assert_equals(navigation.currentEntry.index, 1);
+        assert_equals(navigation.entries().length, start_length + 2);
+        assert_equals(navigation.currentEntry.index, start_index + 1);
         assert_equals(onnavigate_calls, 3);
         history.back();
       } else if (onnavigatesuccess_calls == 4) {
-        assert_equals(navigation.entries().length, 3);
-        assert_equals(navigation.currentEntry.index, 0);
+        assert_equals(navigation.entries().length, start_length + 2);
+        assert_equals(navigation.currentEntry.index, start_index);
         assert_equals(onnavigate_calls, 4);
         t.done();
       }
@@ -30,8 +33,8 @@
     navigation.navigate("?foo").finished
       .then(t.step_func(() => navigation.navigate("?bar").finished))
       .then(t.step_func(() => {
-        assert_equals(navigation.entries().length, 3);
-        assert_equals(navigation.currentEntry.index, 2);
+        assert_equals(navigation.entries().length, start_length + 2);
+        assert_equals(navigation.currentEntry.index, start_index + 2);
         assert_equals(onnavigate_calls, 2);
         history.back();
       }));
diff --git a/testing/web-platform/tests/navigation-api/navigate-event/navigate-destination-dynamic-index.html b/testing/web-platform/tests/navigation-api/navigate-event/navigate-destination-dynamic-index.html
index 2e0f1ea49730f..535e5cfee788c 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/navigate-destination-dynamic-index.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/navigate-destination-dynamic-index.html
@@ -4,6 +4,8 @@
 <script src="../navigation-methods/return-value/resources/helpers.js"></script>
 <script>
 promise_test(async t => {
+  let start_index = navigation.currentEntry.index;
+
   // Wait for after the load event so that the navigation doesn't get converted
   // into a replace navigation.
   await new Promise(resolve => window.onload = () => t.step_timeout(resolve, 0));
@@ -12,7 +14,7 @@
   let back_destination;
   navigation.addEventListener("navigate", t.step_func(e => {
     back_destination = e.destination;
-    assert_equals(back_destination.index, 0);
+    assert_equals(back_destination.index, start_index);
   }), { once: true });
   await navigation.back().finished;
 
@@ -23,7 +25,7 @@
   assert_equals(back_destination.index, -1);
 
   navigation.addEventListener("navigate", t.step_func(e => {
-    assert_equals(e.destination.index, 1);
+    assert_equals(e.destination.index, start_index + 1);
 
     // Dispose the destination entry and destination.index should update.
     navigation.navigate("#clobber_forward");
diff --git a/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-after-fragment.html b/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-after-fragment.html
index ffa9665d66677..9da4ddcd50779 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-after-fragment.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-after-fragment.html
@@ -5,6 +5,7 @@
 async_test(t => {
   window.onload = () => t.step_timeout(() => {
     let start_length = history.length;
+    let start_index = navigation.currentEntry.index;
     let target_key = navigation.currentEntry.key;
     let target_id = navigation.currentEntry.id;
     location.hash = "#1";
@@ -21,7 +22,7 @@
       assert_true(e.destination.sameDocument);
       assert_equals(e.destination.key, target_key);
       assert_equals(e.destination.id, target_id);
-        assert_equals(e.destination.index, 0);
+        assert_equals(e.destination.index, start_index);
       assert_equals(e.formData, null);
       assert_equals(e.sourceElement, null);
     });
diff --git a/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-after-pushState.html b/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-after-pushState.html
index a22eb1bc474e2..fdee41a312191 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-after-pushState.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-after-pushState.html
@@ -4,11 +4,12 @@
 <script>
 async_test(t => {
   window.onload = () => t.step_timeout(() => {
-    let start_length = history.length;
+    let start_history_length = history.length;
+    let start_index = navigation.currentEntry.index;
     let target_key = navigation.currentEntry.key;
     let target_id = navigation.currentEntry.id;
     history.pushState(1, "", "pushState.html");
-    assert_equals(history.length, start_length + 1);
+    assert_equals(history.length, start_history_length + 1);
 
     navigation.onnavigate = t.step_func_done(e => {
       assert_equals(e.navigationType, "traverse");
@@ -21,7 +22,7 @@
       assert_true(e.destination.sameDocument);
       assert_equals(e.destination.key, target_key);
       assert_equals(e.destination.id, target_id);
-      assert_equals(e.destination.index, 0);
+      assert_equals(e.destination.index, start_index);
       assert_equals(e.formData, null);
       assert_equals(e.sourceElement, null);
     });
diff --git a/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-noop.html b/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-noop.html
index 10763c93fd20e..109106b77fcd3 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-noop.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/navigate-history-back-noop.html
@@ -4,6 +4,10 @@
 <iframe id="i" src="/common/blank.html"></iframe>
 <script>
 promise_test(async t => {
+  let start_length = navigation.entries().length;
+  let start_index = navigation.currentEntry.index;
+  let start_history_length = history.length;
+
   // Wait for after the load event so that the navigation doesn't get converted
   // into a replace navigation.
   await new Promise(resolve => window.onload = () => t.step_timeout(resolve, 0));
@@ -11,14 +15,14 @@
   await i.contentWindow.navigation.navigate("#").finished;
   assert_equals(i.contentWindow.navigation.entries().length, 2);
   assert_equals(i.contentWindow.navigation.currentEntry.index, 1);
-  assert_equals(navigation.entries().length, 1);
-  assert_equals(navigation.currentEntry.index, 0);
-  assert_equals(history.length, 2);
+  assert_equals(navigation.entries().length, start_length);
+  assert_equals(navigation.currentEntry.index, start_index);
+  assert_equals(history.length, start_history_length + 1);
 
   i.remove();
-  assert_equals(navigation.entries().length, 1);
-  assert_equals(navigation.currentEntry.index, 0);
-  assert_equals(history.length, 2);
+  assert_equals(navigation.entries().length, start_length);
+  assert_equals(navigation.currentEntry.index, start_index);
+  assert_equals(history.length, start_history_length + 1);
 
   // back() here should do nothing. The iframe that would have navigated has
   // been removed. No navigate event should be fired.
diff --git a/testing/web-platform/tests/navigation-api/navigate-event/navigate-navigation-back-same-document.html b/testing/web-platform/tests/navigation-api/navigate-event/navigate-navigation-back-same-document.html
index e675dcdfe2bf8..b08bbfcbf1143 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/navigate-navigation-back-same-document.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/navigate-navigation-back-same-document.html
@@ -8,6 +8,7 @@
   window.onload = () => t.step_timeout(() => {
     let target_key = navigation.currentEntry.key;
     let target_id = navigation.currentEntry.id;
+    let target_index = navigation.currentEntry.index;
     navigation.navigate("#foo").committed.then(t.step_func(() => {
       navigation.onnavigate = t.step_func_done(e => {
         assert_equals(e.navigationType, "traverse");
@@ -20,7 +21,7 @@
         assert_true(e.destination.sameDocument);
         assert_equals(e.destination.key, target_key);
         assert_equals(e.destination.id, target_id);
-        assert_equals(e.destination.index, 0);
+        assert_equals(e.destination.index, target_index);
         assert_equals(e.formData, null);
         assert_equals(e.info, "hi");
         assert_not_equals(e.hasUAVisualTransition, undefined);
diff --git a/testing/web-platform/tests/navigation-api/navigate-event/navigation-back-same-document-preventDefault.html b/testing/web-platform/tests/navigation-api/navigate-event/navigation-back-same-document-preventDefault.html
index 7edb188823352..f8e31252a42e8 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/navigation-back-same-document-preventDefault.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/navigation-back-same-document-preventDefault.html
@@ -4,13 +4,16 @@
 <script src="../navigation-methods/return-value/resources/helpers.js"></script>
 <script>
 promise_test(async t => {
+  let start_length = navigation.entries().length;
+  let start_index = navigation.currentEntry.index;
+
   // Wait for after the load event so that the navigation doesn't get converted
   // into a replace navigation.
   await new Promise(resolve => window.onload = () => t.step_timeout(resolve, 0));
 
   await navigation.navigate("#").finished;
-  assert_equals(navigation.entries().length, 2);
-  assert_equals(navigation.currentEntry.index, 1);
+  assert_equals(navigation.entries().length, start_length + 1);
+  assert_equals(navigation.currentEntry.index, start_index + 1);
 
   navigation.onnavigate = e => e.preventDefault();
 
@@ -20,7 +23,7 @@
     navigateerror_called = true;
   });
   await assertBothRejectDOM(t, navigation.back(), "AbortError");
-  assert_equals(navigation.currentEntry.index, 1);
+  assert_equals(navigation.currentEntry.index, start_index + 1);
   assert_true(navigateerror_called);
 }, "navigation.back() same-document preventDefault");
 </script>
diff --git a/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-in-iframe-same-document-preventDefault.html b/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-in-iframe-same-document-preventDefault.html
index 463746e8f7977..b3b57f2a1abf8 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-in-iframe-same-document-preventDefault.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-in-iframe-same-document-preventDefault.html
@@ -5,6 +5,9 @@
 <iframe id="i" src="/common/blank.html"></iframe>
 <script>
 promise_test(async t => {
+  let start_length = navigation.entries().length;
+  let start_index = navigation.currentEntry.index;
+
   // Wait for after the load event so that the navigation doesn't get converted
   // into a replace navigation.
   await new Promise(resolve => window.onload = () => t.step_timeout(resolve, 0));
@@ -13,9 +16,9 @@
   // to its initial entry, the top window navigates as well.
   await i.contentWindow.navigation.navigate("#").finished;
   await navigation.navigate("#").finished;
-  assert_equals(navigation.entries().length, 2);
+  assert_equals(navigation.entries().length, start_length + 1);
   assert_equals(i.contentWindow.navigation.entries().length, 2);
-  assert_equals(navigation.currentEntry.index, 1);
+  assert_equals(navigation.currentEntry.index, start_index + 1);
   assert_equals(i.contentWindow.navigation.currentEntry.index, 1);
 
   // Ensure the top window, which is allowed to cancel the traversal, does so.
@@ -37,7 +40,7 @@
   const iDOMException = iWindow.DOMException;
   await assertBothRejectDOM(t, i.contentWindow.navigation.traverseTo(i.contentWindow.navigation.entries()[0].key), "AbortError", iWindow, iDOMException);
   assert_true(top_navigateerror_fired);
-  assert_equals(navigation.currentEntry.index, 1);
+  assert_equals(navigation.currentEntry.index, start_index + 1);
   assert_equals(i.contentWindow.navigation.currentEntry.index, 1);
 }, "navigation.traverseTo() in an iframe with same-document preventDefault in its parent");
 </script>
diff --git a/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-navigates-top-and-same-doc-child-and-cross-doc-child.html b/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-navigates-top-and-same-doc-child-and-cross-doc-child.html
index 31cb54fca2a4d..479f54213a95c 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-navigates-top-and-same-doc-child-and-cross-doc-child.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-navigates-top-and-same-doc-child-and-cross-doc-child.html
@@ -5,6 +5,9 @@
 <iframe id="i2" src="/common/blank.html"></iframe>
 <script>
 promise_test(async t => {
+  let start_length = navigation.entries().length;
+  let start_index = navigation.currentEntry.index;
+
   // Wait for after the load event so that the navigation doesn't get converted
   // into a replace navigation.
   await new Promise(resolve => window.onload = () => t.step_timeout(resolve, 0));
@@ -13,10 +16,10 @@
   i2.contentWindow.navigation.navigate("?");
   await new Promise(resolve => i2.onload = () => t.step_timeout(resolve, 0));
 
-  assert_equals(navigation.entries().length, 2);
+  assert_equals(navigation.entries().length, start_length + 1);
   assert_equals(i1.contentWindow.navigation.entries().length, 2);
   assert_equals(i2.contentWindow.navigation.entries().length, 2);
-  assert_equals(navigation.currentEntry.index, 1);
+  assert_equals(navigation.currentEntry.index, start_index + 1);
   assert_equals(i1.contentWindow.navigation.currentEntry.index, 1);
   assert_equals(i2.contentWindow.navigation.currentEntry.index, 1);
 
@@ -37,12 +40,12 @@
     assert_false(e.cancelable);
   });
 
-  await navigation.traverseTo(navigation.entries()[0].key).finished;
+  await navigation.traverseTo(navigation.entries()[start_index].key).finished;
   // The top window will finish quickly, becuase it is same-document traversal.
   // i2 will be slower because it is cross-document, so wait for its onload.
   await new Promise(resolve => i2.onload = () => t.step_timeout(resolve, 0));
   assert_equals(navigate_event_count, 3);
-  assert_equals(navigation.currentEntry.index, 0);
+  assert_equals(navigation.currentEntry.index, start_index);
   assert_equals(i1.contentWindow.navigation.currentEntry.index, 0);
   assert_equals(i2.contentWindow.navigation.currentEntry.index, 0);
 }, "navigation.traverseTo() can navigate 3 frames of different types with correct navigate event cancelable values");
diff --git a/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-same-document-preventDefault-multiple-windows.html b/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-same-document-preventDefault-multiple-windows.html
index 9bb64fb7cc7a7..61859adb5ee72 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-same-document-preventDefault-multiple-windows.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-same-document-preventDefault-multiple-windows.html
@@ -4,20 +4,23 @@
 <iframe id="i" src="/common/blank.html"></iframe>
 <script>
 promise_test(async t => {
+  let start_length = navigation.entries().length;
+  let start_index = navigation.currentEntry.index;
+
   // Wait for after the load event so that the navigation doesn't get converted
   // into a replace navigation.
   await new Promise(resolve => window.onload = () => t.step_timeout(resolve, 0));
   await navigation.navigate("#").finished;
   await i.contentWindow.navigation.navigate("#").finished;
-  assert_equals(navigation.entries().length, 2);
+  assert_equals(navigation.entries().length, start_length + 1);
   assert_equals(i.contentWindow.navigation.entries().length, 2);
-  assert_equals(navigation.currentEntry.index, 1);
+  assert_equals(navigation.currentEntry.index, start_index + 1);
   assert_equals(i.contentWindow.navigation.currentEntry.index, 1);
 
   navigation.onnavigate = e => e.preventDefault();
   i.contentWindow.navigation.onnavigate = t.unreached_func("navigate event should not fire in the iframe, because the traversal was cancelled in the top window");
-  await promise_rejects_dom(t, "AbortError", navigation.traverseTo(navigation.entries()[0].key).finished);
-  assert_equals(navigation.currentEntry.index, 1);
+  await promise_rejects_dom(t, "AbortError", navigation.traverseTo(navigation.entries()[start_index].key).finished);
+  assert_equals(navigation.currentEntry.index, start_index + 1);
   assert_equals(i.contentWindow.navigation.currentEntry.index, 1);
 }, "navigation.traverseTo() - if a top window cancels the traversal, any iframes should not fire navigate");
 </script>
diff --git a/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-top-cancels-cross-document-child.html b/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-top-cancels-cross-document-child.html
index 11f07afefc523..4ece3ca8cbc01 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-top-cancels-cross-document-child.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/navigation-traverseTo-top-cancels-cross-document-child.html
@@ -5,6 +5,9 @@
 <iframe id="i" src="/common/blank.html"></iframe>
 <script>
 promise_test(async t => {
+  let start_length = navigation.entries().length;
+  let start_index = navigation.currentEntry.index;
+
   // Wait for after the load event so that the navigation doesn't get converted
   // into a replace navigation.
   await new Promise(resolve => window.onload = () => t.step_timeout(resolve, 0));
@@ -12,14 +15,14 @@
   i.contentWindow.navigation.navigate("?");
   await new Promise(resolve => i.onload = () => t.step_timeout(resolve, 0));
 
-  assert_equals(navigation.entries().length, 2);
+  assert_equals(navigation.entries().length, start_length + 1);
   assert_equals(i.contentWindow.navigation.entries().length, 2);
-  assert_equals(navigation.currentEntry.index, 1);
+  assert_equals(navigation.currentEntry.index, start_index + 1);
   assert_equals(i.contentWindow.navigation.currentEntry.index, 1);
 
   navigation.onnavigate = t.step_func(e => e.preventDefault());
   i.contentWindow.navigation.onnavigate = t.unreached_func("navigation should be cancelled before iframe fires navigate event");
-  await assertBothRejectDOM(t, navigation.traverseTo(navigation.entries()[0].key), "AbortError");
+  await assertBothRejectDOM(t, navigation.traverseTo(navigation.entries()[start_index].key), "AbortError");
   // Give the iframe time to navigate in case it was incorrectly permitted.
   await new Promise(resolve => t.step_timeout(resolve, 50));
 }, "navigate.traverseTo() cancelled by top frame cancels cross-document iframe");
diff --git a/testing/web-platform/tests/navigation-api/navigate-event/same-url-replace-cross-document.html b/testing/web-platform/tests/navigation-api/navigate-event/same-url-replace-cross-document.html
index 0a976cd51fdcb..b6bd0cdd88358 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/same-url-replace-cross-document.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/same-url-replace-cross-document.html
@@ -5,10 +5,13 @@
 
 <script>
 promise_test(async t => {
+  let start_length = navigation.entries().length;
+  let start_index = navigation.currentEntry.index;
+
   // Wait for after the load event so that we are definitely testing the
   // same URL as the cause of the rejections.
   await new Promise(resolve => window.onload = () => t.step_timeout(resolve, 0));
-  assert_equals(navigation.entries().length, 1);
+  assert_equals(navigation.entries().length, start_length);
 
   navigation.onnavigate = t.step_func(e => {
     e.intercept();
@@ -17,7 +20,7 @@
   navigation.onnavigateerror = t.unreached_func("onnavigateerror should not be called");
 
   await navigation.navigate(location.href).finished;
-  assert_equals(navigation.entries().length, 1);
-  assert_equals(navigation.currentEntry.index, 0);
+  assert_equals(navigation.entries().length, start_length);
+  assert_equals(navigation.currentEntry.index, start_index);
 }, "navigate() to the current URL cross document should replace");
 </script>
diff --git a/testing/web-platform/tests/navigation-api/navigate-event/same-url-replace-same-document.html b/testing/web-platform/tests/navigation-api/navigate-event/same-url-replace-same-document.html
index 839c687934238..cc4faffe77ab7 100644
--- a/testing/web-platform/tests/navigation-api/navigate-event/same-url-replace-same-document.html
+++ b/testing/web-platform/tests/navigation-api/navigate-event/same-url-replace-same-document.html
@@ -5,19 +5,22 @@
 
 <script>
 promise_test(async t => {
+  let start_length = navigation.entries().length;
+  let start_index = navigation.currentEntry.index;
+
   // Wait for after the load event so that we are definitely testing the
   // same URL as the cause of the rejections.
   await new Promise(resolve => window.onload = () => t.step_timeout(resolve, 0));
-  assert_equals(navigation.entries().length, 1);
+  assert_equals(navigation.entries().length, start_length);
   await navigation.navigate("#").finished;
-  assert_equals(navigation.entries().length, 2);
-  assert_equals(navigation.currentEntry.index, 1);
+  assert_equals(navigation.entries().length, start_length + 1);
+  assert_equals(navigation.currentEntry.index, start_index + 1);
 
   navigation.onnavigate = t.step_func(e => {
     assert_equals(e.navigationType, "replace");
   });
   await navigation.navigate(location.href).finished;
-  assert_equals(navigation.entries().length, 2);
-  assert_equals(navigation.currentEntry.index, 1);
+  assert_equals(navigation.entries().length, start_length + 1);
+  assert_equals(navigation.currentEntry.index, start_index + 1);
 }, "navigate() to the current URL same document should replace");
 </script>