diff --git a/moli-renderer-v8/src/context_bootstrap/form_data_runtime/callbacks.rs b/moli-renderer-v8/src/context_bootstrap/form_data_runtime/callbacks.rs
index 631be945ac..cec84ff741 100644
--- a/moli-renderer-v8/src/context_bootstrap/form_data_runtime/callbacks.rs
+++ b/moli-renderer-v8/src/context_bootstrap/form_data_runtime/callbacks.rs
@@ -10,10 +10,11 @@ use crate::{
     native_bridge::{
         JsContextHost,
         element::{form_associated_form_owner, is_valid_submit_button},
-        node_runtime_and_handle_from_object, throw_dom_exception,
+        node_relevant_context, node_runtime_and_handle_from_object_or_detached,
+        throw_dom_exception,
     },
     util::serialize_v8_iter_array,
-    webidl,
+    web_api_interfaces, webidl,
 };
 use moli_webapi_declare::WebApiObject;
 
@@ -115,77 +116,82 @@ pub(super) fn form_data_constructor_callback<'s>(
         return;
     }
 
-    let mut entries = Vec::new();
     let Some(parsed) = webidl::parse_args::<FormDataConstructorArgs<'s>>(scope, &args) else {
         return;
     };
-    if let Some(form) = parsed.form {
-        let Ok(form) = v8::Local::<v8::Object>::try_from(form) else {
-            throw_type_error(scope, "FormData constructor requires an HTMLFormElement");
-            return;
-        };
-        if object_string_property_defined(scope, form, "tagName")
-            .is_none_or(|tag| !tag.eq_ignore_ascii_case("form"))
-        {
-            throw_type_error(scope, "FormData constructor requires an HTMLFormElement");
-            return;
+    let form = match parsed.form {
+        Some(value) => {
+            let Ok(form) = v8::Local::<v8::Object>::try_from(value) else {
+                throw_type_error(scope, "FormData constructor requires an HTMLFormElement");
+                return;
+            };
+            if !web_api_interfaces::HTMLFormElement::is_instance(scope, form) {
+                throw_type_error(scope, "FormData constructor requires an HTMLFormElement");
+                return;
+            }
+            Some(form)
         }
-        let Ok((form_runtime_ptr, form_handle)) = node_runtime_and_handle_from_object(scope, form)
+        None => None,
+    };
+    // WebIDL converts the optional submitter even when the form is omitted.
+    let submitter = match parsed.submitter {
+        Some(value) if !value.is_null_or_undefined() => {
+            let Ok(submitter) = v8::Local::<v8::Object>::try_from(value) else {
+                throw_type_error(
+                    scope,
+                    "FormData constructor submitter must be an HTMLElement or null",
+                );
+                return;
+            };
+            if !web_api_interfaces::HTMLElement::is_instance(scope, submitter) {
+                throw_type_error(
+                    scope,
+                    "FormData constructor submitter must be an HTMLElement or null",
+                );
+                return;
+            }
+            Some(submitter)
+        }
+        _ => None,
+    };
+    let mut entries = Vec::new();
+    if let Some(form) = form {
+        let Ok((form_runtime_ptr, form_handle)) =
+            node_runtime_and_handle_from_object_or_detached(scope, form)
         else {
             throw_type_error(scope, "FormData constructor requires an HTMLFormElement");
             return;
         };
-        let submitter = match parsed.submitter {
-            Some(value) if value.is_null_or_undefined() => None,
-            Some(value) => match v8::Local::<v8::Object>::try_from(value) {
-                Ok(submitter) => {
-                    let Ok((submitter_runtime_ptr, submitter_handle)) =
-                        node_runtime_and_handle_from_object(scope, submitter)
-                    else {
-                        throw_type_error(
-                            scope,
-                            "FormData constructor submitter must be a submit button",
-                        );
-                        return;
-                    };
-                    if submitter_runtime_ptr != form_runtime_ptr {
-                        throw_dom_exception(
-                            scope,
-                            "NotFoundError",
-                            8,
-                            "The specified element is not owned by this form element.",
-                        );
-                        return;
-                    }
-                    let runtime = unsafe { &*form_runtime_ptr };
-                    if !is_valid_submit_button(runtime, submitter_handle) {
-                        throw_type_error(
-                            scope,
-                            "FormData constructor submitter must be a submit button",
-                        );
-                        return;
-                    }
-                    if form_associated_form_owner(runtime, submitter_handle) != Some(form_handle) {
-                        throw_dom_exception(
-                            scope,
-                            "NotFoundError",
-                            8,
-                            "The specified element is not owned by this form element.",
-                        );
-                        return;
-                    }
-                    Some(submitter)
-                }
-                Err(_) => {
-                    throw_type_error(
-                        scope,
-                        "FormData constructor submitter must be an HTMLElement or null",
-                    );
-                    return;
-                }
-            },
-            None => None,
-        };
+        if let Some(submitter) = submitter {
+            let Ok((submitter_runtime_ptr, submitter_handle)) =
+                node_runtime_and_handle_from_object_or_detached(scope, submitter)
+            else {
+                throw_type_error(
+                    scope,
+                    "FormData constructor submitter must be a submit button",
+                );
+                return;
+            };
+            let runtime = unsafe { &*submitter_runtime_ptr };
+            if !is_valid_submit_button(runtime, submitter_handle) {
+                throw_type_error(
+                    scope,
+                    "FormData constructor submitter must be a submit button",
+                );
+                return;
+            }
+            if submitter_runtime_ptr != form_runtime_ptr
+                || form_associated_form_owner(runtime, submitter_handle) != Some(form_handle)
+            {
+                throw_dom_exception(
+                    scope,
+                    "NotFoundError",
+                    8,
+                    "The specified element is not owned by this form element.",
+                );
+                return;
+            }
+        }
         let Some(next_entries) = construct_form_data_entries_for_form(
             scope,
             form_runtime_ptr,
@@ -219,6 +225,8 @@ pub(crate) fn construct_form_data_entries_for_form<'s>(
         return None;
     }
 
+    let context = node_relevant_context(scope, form).unwrap_or_else(|| scope.get_current_context());
+    let scope = &mut v8::ContextScope::new(scope, context);
     let entries = serialize_form_data_controls(scope, runtime_ptr, form_handle, submitter);
     let entries = dispatch_form_data_event_with_entries(scope, form, &entries).unwrap_or(entries);
     unsafe { &mut *runtime_ptr }.end_form_data_construction(form_handle);
@@ -252,7 +260,7 @@ fn dispatch_form_data_event<'s>(
     form_data: v8::Local<'s, v8::Object>,
 ) {
     let Ok((runtime_ptr, form_handle)) =
-        crate::native_bridge::node_runtime_and_handle_from_object(scope, form)
+        node_runtime_and_handle_from_object_or_detached(scope, form)
     else {
         return;
     };
diff --git a/moli-renderer-v8/src/context_bootstrap/form_data_runtime/serialize.rs b/moli-renderer-v8/src/context_bootstrap/form_data_runtime/serialize.rs
index 1e7194b8c5..64044ca04f 100644
--- a/moli-renderer-v8/src/context_bootstrap/form_data_runtime/serialize.rs
+++ b/moli-renderer-v8/src/context_bootstrap/form_data_runtime/serialize.rs
@@ -7,10 +7,10 @@ use crate::dom::{
 };
 use crate::native_bridge::{
     element::{
-        element_attribute_for_object, element_internals_form_value_for_target,
+        control_has_datalist_ancestor, element_internals_form_value_for_target,
         form_control_is_effectively_disabled, form_data_control_elements, text_control_value,
     },
-    node_runtime_and_handle_from_object,
+    node_runtime_and_handle_from_object_or_detached,
 };
 use moli_encoding::is_charset_sentinel_name;
 use moli_webapi_declare::WebApiObject;
@@ -31,6 +31,9 @@ pub(super) fn serialize_form_data_controls<'s>(
     let mut entries = Vec::new();
     let controls = form_data_control_elements(unsafe { &*runtime_ptr }, form_handle);
     for handle in controls {
+        if control_has_datalist_ancestor(unsafe { &*runtime_ptr }, handle) {
+            continue;
+        }
         let Some(control) = form_data_control_object(scope, runtime_ptr, handle) else {
             continue;
         };
@@ -82,10 +85,6 @@ fn append_form_data_entries_for_control<'s>(
     if control_is_effectively_disabled(scope, control) {
         return;
     }
-    if control_has_datalist_ancestor(scope, control) {
-        return;
-    }
-
     let tag = object_string_property_defined(scope, control, "tagName")
         .map(|tag| tag.to_ascii_lowercase())
         .unwrap_or_default();
@@ -243,19 +242,28 @@ fn append_form_data_entries_for_control<'s>(
     }
 }
 
-fn form_control_name(
-    scope: &mut v8::PinScope<'_, '_>,
-    control: v8::Local<'_, v8::Object>,
+fn form_control_name<'s>(
+    scope: &mut v8::PinScope<'s, '_>,
+    control: v8::Local<'s, v8::Object>,
 ) -> String {
-    element_attribute_for_object(scope, control, "name").unwrap_or_default()
+    let Ok((runtime_ptr, handle)) = node_runtime_and_handle_from_object_or_detached(scope, control)
+    else {
+        return String::new();
+    };
+    unsafe { &*runtime_ptr }
+        .dom_host()
+        .node(handle)
+        .and_then(Node::as_element)
+        .and_then(|element| element.attribute_ns("", "name"))
+        .unwrap_or_default()
+        .to_owned()
 }
 
-fn image_submitter_coordinates(
-    scope: &mut v8::PinScope<'_, '_>,
-    control: v8::Local<'_, v8::Object>,
+fn image_submitter_coordinates<'s>(
+    scope: &mut v8::PinScope<'s, '_>,
+    control: v8::Local<'s, v8::Object>,
 ) -> (u32, u32) {
-    let Ok((runtime_ptr, handle)) =
-        crate::native_bridge::node_runtime_and_handle_from_object(scope, control)
+    let Ok((runtime_ptr, handle)) = node_runtime_and_handle_from_object_or_detached(scope, control)
     else {
         return (0, 0);
     };
@@ -381,9 +389,9 @@ fn push_string_form_data_entry(
     push_form_data_entry(entries, name, v8::Global::new(scope, value));
 }
 
-fn form_control_value(
-    scope: &mut v8::PinScope<'_, '_>,
-    control: v8::Local<'_, v8::Object>,
+fn form_control_value<'s>(
+    scope: &mut v8::PinScope<'s, '_>,
+    control: v8::Local<'s, v8::Object>,
     default: &str,
 ) -> String {
     if let Some(value) = native_form_control_value(scope, control) {
@@ -392,11 +400,12 @@ fn form_control_value(
     object_string_property_defined(scope, control, "value").unwrap_or_else(|| default.to_owned())
 }
 
-fn native_form_control_value(
-    scope: &mut v8::PinScope<'_, '_>,
-    control: v8::Local<'_, v8::Object>,
+fn native_form_control_value<'s>(
+    scope: &mut v8::PinScope<'s, '_>,
+    control: v8::Local<'s, v8::Object>,
 ) -> Option<String> {
-    let (runtime_ptr, handle) = node_runtime_and_handle_from_object(scope, control).ok()?;
+    let (runtime_ptr, handle) =
+        node_runtime_and_handle_from_object_or_detached(scope, control).ok()?;
     let runtime = unsafe { &*runtime_ptr };
     let element = runtime.dom_host().node(handle).and_then(Node::as_element)?;
     if element.is_html_input() {
@@ -427,7 +436,9 @@ fn control_is_effectively_disabled<'s>(
     scope: &mut v8::PinScope<'s, '_>,
     control: v8::Local<'s, v8::Object>,
 ) -> bool {
-    if let Ok((runtime_ptr, handle)) = node_runtime_and_handle_from_object(scope, control) {
+    if let Ok((runtime_ptr, handle)) =
+        node_runtime_and_handle_from_object_or_detached(scope, control)
+    {
         return form_control_is_effectively_disabled(unsafe { &*runtime_ptr }, handle);
     }
     if object_bool_property(scope, control, "disabled").unwrap_or(false) {
@@ -453,7 +464,8 @@ fn native_form_associated_custom_element<'s>(
     scope: &mut v8::PinScope<'s, '_>,
     control: v8::Local<'s, v8::Object>,
 ) -> bool {
-    let Ok((runtime_ptr, handle)) = node_runtime_and_handle_from_object(scope, control) else {
+    let Ok((runtime_ptr, handle)) = node_runtime_and_handle_from_object_or_detached(scope, control)
+    else {
         return false;
     };
     is_form_associated_custom_element_handle(unsafe { &*runtime_ptr }, handle)
@@ -488,23 +500,6 @@ fn control_is_in_first_legend<'s>(
     false
 }
 
-fn control_has_datalist_ancestor<'s>(
-    scope: &mut v8::PinScope<'s, '_>,
-    control: v8::Local<'s, v8::Object>,
-) -> bool {
-    let mut current = object_property_as_object(scope, control, "parentElement");
-    while let Some(element) = current {
-        let tag = object_string_property_defined(scope, element, "tagName")
-            .map(|tag| tag.to_ascii_lowercase())
-            .unwrap_or_default();
-        if tag == "datalist" {
-            return true;
-        }
-        current = object_property_as_object(scope, element, "parentElement");
-    }
-    false
-}
-
 fn option_is_disabled(scope: &mut v8::PinScope<'_, '_>, option: v8::Local<'_, v8::Object>) -> bool {
     let mut current = Some(option);
     while let Some(element) = current {
diff --git a/moli-renderer-v8/src/native_bridge/element.rs b/moli-renderer-v8/src/native_bridge/element.rs
index 403341ece0..29effdfae8 100644
--- a/moli-renderer-v8/src/native_bridge/element.rs
+++ b/moli-renderer-v8/src/native_bridge/element.rs
@@ -105,9 +105,9 @@ use trusted_types::{
 };
 
 pub(crate) use forms::{
-    autocomplete_field_name, autofill_related_form_control_elements, form_associated_form_owner,
-    form_control_elements, form_data_control_elements, is_valid_submit_button,
-    submit_form_with_submit_event,
+    autocomplete_field_name, autofill_related_form_control_elements, control_has_datalist_ancestor,
+    form_associated_form_owner, form_control_elements, form_data_control_elements,
+    is_valid_submit_button, submit_form_with_submit_event,
 };
 pub(in crate::native_bridge) use forms::{form_named_control_matches, form_named_image_matches};
 #[cfg(test)]
diff --git a/moli-renderer-v8/src/native_bridge/element/forms.rs b/moli-renderer-v8/src/native_bridge/element/forms.rs
index 0477a6431e..7ddd9aee44 100644
--- a/moli-renderer-v8/src/native_bridge/element/forms.rs
+++ b/moli-renderer-v8/src/native_bridge/element/forms.rs
@@ -245,6 +245,7 @@ pub(in crate::native_bridge) use self::text_control::{
     text_control_set_selection_range_callback, textarea_value_getter_function,
     textarea_value_setter_function,
 };
+pub(crate) use self::validation::control_has_datalist_ancestor;
 pub(crate) use self::validation::v8_pattern_is_usable;
 pub(in crate::native_bridge) use self::validation::{
     control_check_validity_callback, control_matches_validity_pseudo,
diff --git a/moli-renderer-v8/src/native_bridge/element/forms/validation.rs b/moli-renderer-v8/src/native_bridge/element/forms/validation.rs
index b2c1c9b9fb..4481ce9c42 100644
--- a/moli-renderer-v8/src/native_bridge/element/forms/validation.rs
+++ b/moli-renderer-v8/src/native_bridge/element/forms/validation.rs
@@ -488,7 +488,7 @@ fn required_value_missing_is_suppressed_for_immutable_control(
             || (element.is_html_input() && element.input_type().supports_readonly()))
 }
 
-fn control_has_datalist_ancestor(runtime: &JsContextHost, handle: DomHandle) -> bool {
+pub(crate) fn control_has_datalist_ancestor(runtime: &JsContextHost, handle: DomHandle) -> bool {
     let mut current = runtime.dom_host().parent_node(handle);
     while let Some(parent) = current {
         let Some(parent_element) = runtime.dom_host().node(parent).and_then(Node::as_element)
diff --git a/moli-renderer-v8/src/script_vm/tests/dom_elements/form_data_brands.js b/moli-renderer-v8/src/script_vm/tests/dom_elements/form_data_brands.js
new file mode 100644
index 0000000000..c7fd3d83de
--- /dev/null
+++ b/moli-renderer-v8/src/script_vm/tests/dom_elements/form_data_brands.js
@@ -0,0 +1,84 @@
+(() => {
+  const globals = [window, document.getElementById('child').contentWindow];
+  const rows = [], errors = [];
+  for (let realm = 0; realm < globals.length; ++realm) {
+    const g = globals[realm], other = globals[1 - realm];
+    for (const kind of ['live', 'windowless', 'parsed']) {
+      const label = `${realm}/${kind}`;
+      try {
+        const d = kind === 'live' ? g.document : kind === 'windowless' ?
+          g.document.implementation.createHTMLDocument('') :
+          new g.DOMParser().parseFromString('<!doctype html><body>', 'text/html');
+        const form = d.createElement('form'), input = d.createElement('input');
+        input.setAttribute('name', 'input-name'); input.setAttribute('value', 'input-value');
+        form.appendChild(input);
+        const select = d.createElement('select'), option = d.createElement('option');
+        select.setAttribute('name', 'select-name'); option.setAttribute('value', 'option-value');
+        select.appendChild(option); form.appendChild(select);
+        const button = d.createElement('button');
+        button.setAttribute('type', 'submit'); button.setAttribute('name', 'send'); button.setAttribute('value', 'button');
+        form.appendChild(button);
+        let tagReads = 0;
+        Object.defineProperty(form, 'tagName', {configurable: true, get() { ++tagReads; throw new Error('author tag getter'); }});
+        let valueReads = 0;
+        Object.defineProperty(input, 'value', {configurable: true, get() { ++valueReads; throw new Error('author value getter'); }});
+        let eventCount = 0, eventRealm = true, eventTarget = true;
+        form.addEventListener('formdata', event => {
+          ++eventCount;
+          eventRealm &&= event instanceof g.FormDataEvent && event.formData instanceof g.FormData;
+          eventTarget &&= event.target === form;
+          event.formData.append('from-handler', 'listener');
+        });
+        const data = new other.FormData(form);
+        const checks = {constructorRealm: Object.getPrototypeOf(data) === other.FormData.prototype,
+          input: data.get('input-name') === 'input-value',
+          option: data.get('select-name') === 'option-value',
+          event: eventCount === 1 && eventRealm && eventTarget,
+          handlerMutation: data.get('from-handler') === 'listener',
+          nativeProperties: tagReads === 0 && valueReads === 0,
+          omitSubmitter: !data.has('send')};
+        const withSubmitter = new other.FormData(form, button);
+        checks.submitter = withSubmitter.get('send') === 'button' && eventCount === 2;
+        let traps = 0;
+        const author = new g.Proxy(form, {get() { ++traps; return undefined; }, getPrototypeOf() { ++traps; return null; }});
+        const revoked = g.Proxy.revocable(form, {}); revoked.revoke();
+        checks.invalidForms = true;
+        for (const invalid of [null, {}, g.Object.create(form), author, revoked.proxy,
+          d.createElement('div'), d.createElementNS('http://www.w3.org/2000/svg', 'form')]) {
+          let error;
+          try { new other.FormData(invalid); } catch (caught) { error = caught; }
+          checks.invalidForms &&= error instanceof other.TypeError;
+        }
+        checks.invalidSubmitters = true;
+        for (const invalid of [{}, g.Object.create(button), new g.Proxy(button, {get() { ++traps; }}),
+          d.createElement('div'), other.document.createElement('div')]) {
+          let error;
+          try { new other.FormData(form, invalid); } catch (caught) { error = caught; }
+          checks.invalidSubmitters &&= error instanceof other.TypeError;
+        }
+        const foreign = d.createElement('button'); foreign.type = 'submit';
+        const crossDocument = other.document.createElement('button'); crossDocument.type = 'submit';
+        checks.foreignSubmitter = true;
+        for (const submitter of [foreign, crossDocument]) {
+          let notFound;
+          try { new other.FormData(form, submitter); } catch (caught) { notFound = caught; }
+          checks.foreignSubmitter &&= notFound instanceof other.DOMException && notFound.name === 'NotFoundError';
+        }
+        let omittedSubmitterError;
+        try { new other.FormData(undefined, {}); }
+        catch (error) { omittedSubmitterError = error; }
+        checks.omittedFormStillConvertsSubmitter = omittedSubmitterError instanceof other.TypeError;
+        checks.noPublicReads = traps === 0 && tagReads === 0 && valueReads === 0;
+        other.document.adoptNode(form);
+        const adoptedData = new other.FormData(form);
+        checks.adoptedFormRealm = eventCount === 3 && eventRealm && eventTarget &&
+          Object.getPrototypeOf(adoptedData) === other.FormData.prototype &&
+          adoptedData.get('from-handler') === 'listener';
+        rows.push({label, checks});
+      } catch (error) { errors.push({label, message: String(error)}); }
+    }
+  }
+  globalThis.__uiEventResults = {rows, errors,
+    passed: errors.length === 0 && rows.every(row => Object.values(row.checks).every(value => value === true))};
+  return __uiEventResults.passed;
+})()
diff --git a/moli-renderer-v8/src/script_vm/tests/dom_elements/form_data_brands.rs b/moli-renderer-v8/src/script_vm/tests/dom_elements/form_data_brands.rs
new file mode 100644
index 0000000000..eb73d5fbbd
--- /dev/null
+++ b/moli-renderer-v8/src/script_vm/tests/dom_elements/form_data_brands.rs
@@ -0,0 +1,33 @@
+use super::*;
+
+#[tokio::test]
+async fn form_data_constructor_accepts_native_forms_across_document_realms() {
+    let loader = ResourceRequestClient::new(&moli_fetch::FetchConfig::default()).unwrap();
+    let mut vm = new_storage_page_task_executor_test_vm_with_loader(
+        "https://form-data-brands.test/",
+        &loader,
+    );
+    vm.eval(
+        r#"
+      if (!document.documentElement) document.appendChild(document.createElement('html'));
+      if (!document.body) document.documentElement.appendChild(document.createElement('body'));
+      const frame=document.body.appendChild(document.createElement('iframe'));
+      frame.id='child'; frame.srcdoc='<body></body>'; void frame.contentWindow;
+      'ready'
+    "#,
+    )
+    .unwrap();
+    assert!(
+        vm.run_one_child_frame_task_executor_turn(
+            ChildFrameSemanticTurnKind::RealmMaterialization,
+            &loader,
+        )
+        .await
+        .unwrap()
+    );
+    vm.drain_ready_page_task_executor_turns_for_setup(&loader, 128)
+        .await
+        .unwrap();
+    assert_eq!(vm.eval(include_str!("form_data_brands.js")).unwrap(), "true", "{}",
+        vm.eval("JSON.stringify({errors:__uiEventResults.errors,failures:__uiEventResults.rows.filter(row=>Object.values(row.checks).some(value=>value!==true))})").unwrap());
+}
diff --git a/moli-renderer-v8/src/script_vm/tests/dom_elements/mod.rs b/moli-renderer-v8/src/script_vm/tests/dom_elements/mod.rs
index 7000e0114d..9ea50f38cf 100644
--- a/moli-renderer-v8/src/script_vm/tests/dom_elements/mod.rs
+++ b/moli-renderer-v8/src/script_vm/tests/dom_elements/mod.rs
@@ -5,6 +5,7 @@ mod custom_elements;
 mod detached;
 mod dom_surface;
 mod focus;
+mod form_data_brands;
 mod live_document;
 mod text_controls;
 mod wrapper_identity;