diff --git a/moli-core/tests/fixtures/document-default-view.js b/moli-core/tests/fixtures/document-default-view.js
new file mode 100644
index 0000000000..a487fd4744
--- /dev/null
+++ b/moli-core/tests/fixtures/document-default-view.js
@@ -0,0 +1,99 @@
+(async () => {
+  const result = {checks: 0, failures: [], observations: []};
+  const check = (name, action, expected = true) => {
+    result.checks++;
+    try {
+      const actual = action();
+      if (actual !== expected) result.failures.push({name, actual, expected});
+    } catch (error) { result.failures.push({name, error: error.name, message: error.message}); }
+  };
+  const tick = () => new Promise(resolve => setTimeout(resolve, 0));
+  const url = name => '/compat/child-dynamic-markup-document?markup=' + name;
+  const frame = async (owner, name) => {
+    const node = owner.createElement('iframe');
+    const loaded = new Promise(resolve => node.onload = resolve);
+    node.src = url(name);
+    owner.body.append(node);
+    await loaded;
+    return node;
+  };
+  const getter = Object.getOwnPropertyDescriptor(Document.prototype, 'defaultView').get;
+  const popup = window.open('about:blank', 'default-view-probe');
+  if (!popup) {result.failures.push({name: 'popup-open', message: 'popup was blocked'}); return result;}
+  const popupDoc = popup.document;
+  check('popup-live', () => popupDoc.defaultView === popup);
+  check('root', () => document.defaultView === window);
+  for (const [label, doc] of [
+    ['constructor', new Document()],
+    ['html-document', document.implementation.createHTMLDocument('')],
+    ['xml-document', document.implementation.createDocument(null, 'root')],
+    ['parser', new DOMParser().parseFromString('<p>text</p>', 'text/html')],
+    ['clone', document.cloneNode(false)],
+  ]) check(label, () => doc.defaultView === null);
+
+  const blank = document.createElement('iframe');
+  document.body.append(blank);
+  const blankDoc = blank.contentDocument, blankForms = blankDoc.forms;
+  const blankWin = blank.contentWindow;
+  check('initial-blank-view', () => blankDoc.defaultView === blankWin);
+  check('initial-blank-collection-realm', () => Object.getPrototypeOf(blankForms) === blankWin.HTMLCollection.prototype);
+  blank.remove();
+  check('initial-blank-removed-null', () => blankDoc.defaultView === null);
+
+  for (const mode of ['remove', 'parent-navigation', 'parent-open', 'self-navigation', 'reinsert']) {
+    const parentFrame = await frame(document, 'parent');
+    const child = await frame(parentFrame.contentDocument, 'child');
+    const doc = child.contentDocument, win = child.contentWindow;
+    const childGetter = Object.getOwnPropertyDescriptor(win.Document.prototype, 'defaultView').get;
+    const collectionPrototype = win.HTMLCollection.prototype;
+    const elementPrototype = win.HTMLDivElement.prototype;
+    check(mode + ':live', () => doc.defaultView === win);
+    check(mode + ':borrowed-live', () => getter.call(doc) === win);
+    check(mode + ':child-getter-root', () => childGetter.call(document) === window);
+    if (mode === 'remove' || mode === 'reinsert') {
+      child.remove();
+      check(mode + ':synchronous-null', () => doc.defaultView === null);
+      if (mode === 'reinsert') {
+        const loaded = new Promise(resolve => child.onload = resolve);
+        child.src = url('replacement'); parentFrame.contentDocument.body.append(child);
+        await loaded;
+      }
+    } else if (mode === 'parent-open') {
+      parentFrame.contentDocument.open(); parentFrame.contentDocument.close();
+    } else {
+      const target = mode === 'self-navigation' ? child : parentFrame;
+      const loaded = new Promise(resolve => target.onload = resolve);
+      target.src = url('replacement'); await loaded;
+    }
+    await tick();
+    check(mode + ':discarded-null', () => doc.defaultView === null);
+    check(mode + ':borrowed-null', () => getter.call(doc) === null);
+    check(mode + ':old-realm-getter-null', () => childGetter.call(doc) === null);
+    check(mode + ':old-realm-getter-root', () => childGetter.call(document) === window);
+    check(mode + ':collection-realm', () => Object.getPrototypeOf(doc.forms) === collectionPrototype);
+    check(mode + ':element-realm', () => Object.getPrototypeOf(doc.createElement('div')) === elementPrototype);
+    check(mode + ':open-identity', () => doc.open() === doc);
+    check(mode + ':open-remains-null', () => doc.defaultView === null);
+    doc.close();
+    if (mode === 'self-navigation' || mode === 'reinsert') {
+      check(mode + ':new-document', () => child.contentDocument !== doc);
+      check(mode + ':new-defaultView', () => child.contentDocument.defaultView === child.contentWindow);
+    }
+    parentFrame.remove();
+  }
+  const live = await frame(document, 'stream');
+  const liveDoc = live.contentDocument, liveWin = live.contentWindow;
+  liveDoc.open(); liveDoc.write('<p>replacement</p>'); liveDoc.close();
+  check('document-open-keeps-view', () => liveDoc.defaultView === liveWin);
+  live.remove(); await tick();
+  check('document-open-removed-null', () => liveDoc.defaultView === null);
+
+  popup.close();
+  // Closing a top-level browsing context is asynchronous, even after closed becomes true.
+  for (let i = 0; i < 100 && (!popup.closed || popupDoc.defaultView !== null); i++) {
+    await new Promise(resolve => setTimeout(resolve, 10));
+  }
+  check('popup-closed', () => popup.closed);
+  check('popup-discarded-null', () => popupDoc.defaultView === null);
+  return result;
+})()
diff --git a/moli-core/tests/scripts.rs b/moli-core/tests/scripts.rs
index 9725967cb5..88372b4522 100644
--- a/moli-core/tests/scripts.rs
+++ b/moli-core/tests/scripts.rs
@@ -34,6 +34,9 @@ mod document_close;
 #[path = "scripts/document_open_url.rs"]
 mod document_open_url;
 
+#[path = "scripts/document_default_view.rs"]
+mod document_default_view;
+
 #[path = "scripts/retained_child_window.rs"]
 mod retained_child_window;
 
diff --git a/moli-core/tests/scripts/document_default_view.rs b/moli-core/tests/scripts/document_default_view.rs
new file mode 100644
index 0000000000..7c45bb5df1
--- /dev/null
+++ b/moli-core/tests/scripts/document_default_view.rs
@@ -0,0 +1,29 @@
+use super::*;
+
+#[tokio::test(flavor = "multi_thread")]
+async fn document_default_view_tracks_browsing_context_without_retargeting_its_realm() -> Result<()>
+{
+    let server = FixtureServer::spawn().await?;
+    let browser = Browser::new(AppConfig::default())?;
+    let mut page = browser
+        .fetch(&server.url("/compat/child-dynamic-markup-document?markup=entry"))
+        .await?;
+    let script = include_str!("../fixtures/document-default-view.js");
+    let result = tokio::time::timeout(
+        Duration::from_secs(10),
+        page.evaluate_runtime_expression_with_await_async(
+            &format!("({script}).then(JSON.stringify)"),
+            true,
+        ),
+    )
+    .await??;
+    let observed: serde_json::Value = serde_json::from_str(
+        result["value"]
+            .as_str()
+            .expect("Document defaultView observations"),
+    )?;
+    assert_eq!(observed["checks"], 75);
+    assert_eq!(observed["failures"], serde_json::json!([]), "{observed}");
+    server.shutdown().await;
+    Ok(())
+}
diff --git a/moli-renderer-v8/src/native_bridge/context_host/activity.rs b/moli-renderer-v8/src/native_bridge/context_host/activity.rs
index f17482dcc0..b79454254e 100644
--- a/moli-renderer-v8/src/native_bridge/context_host/activity.rs
+++ b/moli-renderer-v8/src/native_bridge/context_host/activity.rs
@@ -3,8 +3,11 @@ use super::*;
 
 impl JsContextHost {
     pub(crate) fn document_has_browsing_context(&self, document: DomHandle) -> bool {
-        // A detached iframe compatibility window can be a document's defaultView
-        // without registering a browsing context. Check the native association.
+        if self.page_context_resources_closed() {
+            return false;
+        }
+        // Retained or synthetic Window associations do not establish a live
+        // browsing context. Consult the actual document owners instead.
         self.dom_host().document_handle() == document
             || self
                 .child_browsing_context_host_for_document_handle(document)
diff --git a/moli-renderer-v8/src/native_bridge/context_host/mod.rs b/moli-renderer-v8/src/native_bridge/context_host/mod.rs
index 85df005c15..f19ad39206 100644
--- a/moli-renderer-v8/src/native_bridge/context_host/mod.rs
+++ b/moli-renderer-v8/src/native_bridge/context_host/mod.rs
@@ -1396,6 +1396,10 @@ impl JsContextHost {
         self.deferred_context_host_release_queue = queue;
     }
 
+    pub(crate) fn page_context_resources_closed(&self) -> bool {
+        self.page_context_resources_closed
+    }
+
     pub(crate) fn close_page_context_resources_for_teardown(&mut self) {
         self.mark_page_context_detached();
         if self.page_context_resources_closed {
diff --git a/moli-renderer-v8/src/native_bridge/document.rs b/moli-renderer-v8/src/native_bridge/document.rs
index d8f91a2ece..feed83b5f1 100644
--- a/moli-renderer-v8/src/native_bridge/document.rs
+++ b/moli-renderer-v8/src/native_bridge/document.rs
@@ -16,7 +16,7 @@ use super::super::{
 };
 use super::element::{canonical_dir_value, element_attribute, set_reflected_attribute};
 use super::node::{
-    node_is_document, node_runtime_and_handle_from_object,
+    node_is_document, node_relevant_context, node_runtime_and_handle_from_object,
     node_runtime_and_handle_from_object_or_detached,
 };
 use super::{
@@ -1568,12 +1568,10 @@ fn document_html_collection_getter<'s>(
         );
         return;
     };
-    // A child Document wrapper can precede its Window realm. Follow the
-    // associated Window once available, including through a borrowed getter.
-    let context = document_associated_window_for_object(scope, runtime_ptr, handle, receiver)
-        .and_then(|window| window.get_creation_context(scope))
-        .or_else(|| receiver.get_creation_context(scope))
-        .expect("Document must have a creation context");
+    // A WindowProxy can already target a newer realm after navigation. The
+    // collection still belongs to the retained Document's own realm.
+    let context =
+        node_relevant_context(scope, receiver).expect("Document must have a creation context");
     let scope = &mut v8::ContextScope::new(scope, context);
     let collection = collections::build_live_collection_for_node(
         scope,
@@ -1598,6 +1596,10 @@ fn document_default_view_getter_function<'s>(
         rv.set_null();
         return;
     };
+    if !document_has_browsing_context(unsafe { &*runtime_ptr }, handle) {
+        rv.set_null();
+        return;
+    }
     match document_associated_window_for_object(scope, runtime_ptr, handle, args.this()) {
         Some(window) => rv.set(window.into()),
         None => rv.set_null(),
diff --git a/moli-renderer-v8/src/native_bridge/document/detached_install/accessors/iframe_window.rs b/moli-renderer-v8/src/native_bridge/document/detached_install/accessors/iframe_window.rs
index ebdf83da54..24849396e1 100644
--- a/moli-renderer-v8/src/native_bridge/document/detached_install/accessors/iframe_window.rs
+++ b/moli-renderer-v8/src/native_bridge/document/detached_install/accessors/iframe_window.rs
@@ -3,7 +3,10 @@ use crate::web_api_interfaces;
 use moli_webapi_declare::WebApiObject;
 use url::Url;
 
-use crate::native_bridge::document::set_document_associated_window;
+use crate::native_bridge::document::{
+    document_associated_window_for_object, set_document_associated_window,
+};
+use crate::native_bridge::node_runtime_and_handle_from_object_or_detached;
 
 use super::super::super::detached_owner_document_object;
 use super::iframe_style::install_detached_iframe_get_computed_style;
@@ -57,7 +60,8 @@ fn detached_iframe_parent_window<'s>(
     scope: &mut v8::PinScope<'s, '_>,
     iframe: v8::Local<'s, v8::Object>,
 ) -> Option<v8::Local<'s, v8::Object>> {
-    detached_owner_document_object(scope, iframe)?
-        .get(scope, v8str(scope, "defaultView").into())
-        .and_then(|value| v8::Local::<v8::Object>::try_from(value).ok())
+    let document = detached_owner_document_object(scope, iframe)?;
+    let (runtime_ptr, handle) =
+        node_runtime_and_handle_from_object_or_detached(scope, document).ok()?;
+    document_associated_window_for_object(scope, runtime_ptr, handle, document)
 }
diff --git a/moli-renderer-v8/src/script_vm/tests/dom_elements/detached/document_lifecycle_and_adoption.rs b/moli-renderer-v8/src/script_vm/tests/dom_elements/detached/document_lifecycle_and_adoption.rs
index c3a27efc6c..73e3022ab9 100644
--- a/moli-renderer-v8/src/script_vm/tests/dom_elements/detached/document_lifecycle_and_adoption.rs
+++ b/moli-renderer-v8/src/script_vm/tests/dom_elements/detached/document_lifecycle_and_adoption.rs
@@ -741,58 +741,6 @@ fn domparser_xml_preserves_content_type_and_document_interface_for_success_and_e
     );
 }
 
-#[test]
-fn detached_iframe_windows_do_not_change_document_visibility() {
-    let mut vm = new_storage_test_vm("https://detached-iframe-visibility.test/");
-
-    let result = vm
-        .eval(
-            r#"
-(() => {
-  const errors = [];
-  const check = (condition, message) => { if (!condition) errors.push(message); };
-  const factories = [
-    ["createHTMLDocument", () => document.implementation.createHTMLDocument("")],
-    ["DOMParser", () => new DOMParser().parseFromString("<body></body>", "text/html")],
-    ["createDocument", () => document.implementation.createDocument("urn:test", "root", null)]
-  ];
-  for (const [name, create] of factories) {
-    for (const first of ["document", "window"]) {
-      const outer = create();
-      const frame = outer.createElementNS("http://www.w3.org/1999/xhtml", "iframe");
-      frame.srcdoc = "<p>hello</p>";
-      outer.documentElement.appendChild(frame);
-      const label = `${name}/${first}`;
-      check(outer.defaultView === null, `${label}: windowless owner`);
-      let child;
-      if (first === "document") {
-        child = frame.contentDocument;
-        check(child.hidden && child.visibilityState === "hidden", `${label}: before contentWindow`);
-      }
-      const view = frame.contentWindow;
-      child ||= frame.contentDocument;
-      check(view !== null && view.document === child, `${label}: synthetic window`);
-      check(child.defaultView === view, `${label}: associated window retained`);
-      check(child.hidden && child.visibilityState === "hidden", `${label}: after contentWindow`);
-      check(outer.hidden && outer.visibilityState === "hidden", `${label}: owner stays hidden`);
-      const nested = child.createElement("iframe");
-      nested.srcdoc = "<p>nested</p>";
-      child.body.appendChild(nested);
-      const nestedChild = nested.contentDocument;
-      check(nestedChild.hidden && nestedChild.visibilityState === "hidden", `${label}: nested before contentWindow`);
-      check(nested.contentWindow.document === nestedChild, `${label}: nested window`);
-      check(nestedChild.hidden && nestedChild.visibilityState === "hidden", `${label}: nested after contentWindow`);
-    }
-  }
-  return JSON.stringify(errors);
-})()
-"#,
-        )
-        .expect("detached iframe visibility probe should evaluate");
-
-    assert_eq!(result, "[]");
-}
-
 #[test]
 fn body_legacy_colors_treat_null_as_empty_before_reflection() {
     let mut vm = new_parsed_test_vm(
diff --git a/moli-renderer-v8/src/script_vm/tests/dom_elements/detached/tables_and_document_surfaces.rs b/moli-renderer-v8/src/script_vm/tests/dom_elements/detached/tables_and_document_surfaces.rs
index 5249c8380d..8cb6f9c490 100644
--- a/moli-renderer-v8/src/script_vm/tests/dom_elements/detached/tables_and_document_surfaces.rs
+++ b/moli-renderer-v8/src/script_vm/tests/dom_elements/detached/tables_and_document_surfaces.rs
@@ -1639,3 +1639,57 @@ fn table_legacy_dom_string_reflectors_use_owner_prototype() {
 
     assert_eq!(result, "ok");
 }
+
+#[test]
+fn detached_iframe_windows_do_not_create_document_browsing_contexts() {
+    let mut vm = new_storage_test_vm("https://detached-iframe-visibility.test/");
+
+    let result = vm
+        .eval(
+            r#"
+(() => {
+  const errors = [];
+  const check = (condition, message) => { if (!condition) errors.push(message); };
+  const factories = [
+    ["createHTMLDocument", () => document.implementation.createHTMLDocument("")],
+    ["DOMParser", () => new DOMParser().parseFromString("<body></body>", "text/html")],
+    ["createDocument", () => document.implementation.createDocument("urn:test", "root", null)]
+  ];
+  for (const [name, create] of factories) {
+    for (const first of ["document", "window"]) {
+      const outer = create();
+      const frame = outer.createElementNS("http://www.w3.org/1999/xhtml", "iframe");
+      frame.srcdoc = "<p>hello</p>";
+      outer.documentElement.appendChild(frame);
+      const label = `${name}/${first}`;
+      check(outer.defaultView === null, `${label}: windowless owner`);
+      let child;
+      if (first === "document") {
+        child = frame.contentDocument;
+        check(child.hidden && child.visibilityState === "hidden", `${label}: before contentWindow`);
+      }
+      const view = frame.contentWindow;
+      child ||= frame.contentDocument;
+      check(view !== null && view.document === child, `${label}: synthetic window`);
+      check(child.defaultView === null, `${label}: synthetic window has no browsing context`);
+      check(child.hidden && child.visibilityState === "hidden", `${label}: after contentWindow`);
+      check(outer.hidden && outer.visibilityState === "hidden", `${label}: owner stays hidden`);
+      const nested = child.createElement("iframe");
+      nested.srcdoc = "<p>nested</p>";
+      child.body.appendChild(nested);
+      const nestedChild = nested.contentDocument;
+      check(nestedChild.hidden && nestedChild.visibilityState === "hidden", `${label}: nested before contentWindow`);
+      check(nested.contentWindow.document === nestedChild, `${label}: nested window`);
+      check(nested.contentWindow.parent === view, `${label}: nested compatibility parent`);
+      check(nestedChild.defaultView === null, `${label}: nested synthetic window has no browsing context`);
+      check(nestedChild.hidden && nestedChild.visibilityState === "hidden", `${label}: nested after contentWindow`);
+    }
+  }
+  return JSON.stringify(errors);
+})()
+"#,
+        )
+        .expect("detached iframe visibility probe should evaluate");
+
+    assert_eq!(result, "[]");
+}
diff --git a/moli-renderer-v8/src/script_vm/tests/dom_elements/live_document/document_bindings.rs b/moli-renderer-v8/src/script_vm/tests/dom_elements/live_document/document_bindings.rs
index c834dce1c4..e4eb636415 100644
--- a/moli-renderer-v8/src/script_vm/tests/dom_elements/live_document/document_bindings.rs
+++ b/moli-renderer-v8/src/script_vm/tests/dom_elements/live_document/document_bindings.rs
@@ -1,5 +1,19 @@
 use super::*;
 
+#[test]
+fn document_default_view_is_null_after_main_context_teardown() {
+    let mut vm = new_storage_test_vm("https://document-default-view-teardown.test/");
+    vm.eval("globalThis.retainedDocument = document;").unwrap();
+    vm._context_host
+        .borrow_mut()
+        .close_page_context_resources_for_teardown();
+    assert_eq!(
+        vm.eval("String(retainedDocument.defaultView === null)")
+            .expect("retained Document should remain readable after context teardown"),
+        "true"
+    );
+}
+
 #[test]
 fn input_show_picker_enforces_brand_without_rejecting_inherited_child_origin() {
     let mut vm = new_storage_test_vm("https://show-picker-origin.test/");