diff --git a/dom/base/AncestorIterator.h b/dom/base/AncestorIterator.h
index 2c8a9b6ed325..1dc7cc5824ae 100644
--- a/dom/base/AncestorIterator.h
+++ b/dom/base/AncestorIterator.h
@@ -50,6 +50,7 @@ namespace dom {
     nsINode* mCurrent;                                                   \
   };                                                                     \
   class name_ : public Inclusive##name_ {                                \
+   public:                                                               \
     using Super = Inclusive##name_;                                      \
     explicit name_(const nsINode& aNode)                                 \
         : Inclusive##name_(aNode.method_()) {}                           \
diff --git a/dom/base/FilteredNodeIterator.h b/dom/base/FilteredNodeIterator.h
index 359a527de2f3..ce64fa65c81b 100644
--- a/dom/base/FilteredNodeIterator.h
+++ b/dom/base/FilteredNodeIterator.h
@@ -23,6 +23,11 @@ class FilteredNodeIterator : public Iter {
     EnsureValid();
   }
 
+  static T* First(const nsINode& aNode) {
+    FilteredNodeIterator iter(aNode);
+    return *iter;
+  }
+
   FilteredNodeIterator& begin() { return *this; }
   using Iter::end;
 
diff --git a/dom/html/HTMLFormSubmission.cpp b/dom/html/HTMLFormSubmission.cpp
index 7b6370deb099..0d723f6a7c78 100644
--- a/dom/html/HTMLFormSubmission.cpp
+++ b/dom/html/HTMLFormSubmission.cpp
@@ -30,6 +30,7 @@
 #include "nsCExternalHandlerService.h"
 #include "nsContentUtils.h"
 
+#include "mozilla/dom/AncestorIterator.h"
 #include "mozilla/dom/Directory.h"
 #include "mozilla/dom/File.h"
 #include "mozilla/StaticPrefs_dom.h"
@@ -831,14 +832,8 @@ nsresult HTMLFormSubmission::GetFromForm(HTMLFormElement* aForm,
   }
 
   if (method == NS_FORM_METHOD_DIALOG) {
-    HTMLDialogElement* dialog = nullptr;
-    for (nsIContent* parent = aForm->GetParent(); parent;
-         parent = parent->GetParent()) {
-      dialog = HTMLDialogElement::FromNodeOrNull(parent);
-      if (dialog) {
-        break;
-      }
-    }
+    HTMLDialogElement* dialog =
+        AncestorsOfType<HTMLDialogElement>::First(*aForm);
 
     // If there isn't one, or if it does not have an open attribute, do
     // nothing.