2 files changed, 15 insertions, 0 deletions
diff --git a/layout/generic/DetailsFrame.cpp b/layout/generic/DetailsFrame.cpp
index 1d28bbe96..389a476cb 100644
--- a/layout/generic/DetailsFrame.cpp
+++ b/layout/generic/DetailsFrame.cpp
@@ -129,3 +129,12 @@ DetailsFrame::AppendAnonymousContentTo(nsTArray<nsIContent*>& aElements,
     aElements.AppendElement(mDefaultSummary);
   }
 }
+
+bool
+DetailsFrame::HasMainSummaryFrame(nsIFrame* aSummaryFrame)
+{
+  nsIFrame* firstChild =
+    nsPlaceholderFrame::GetRealFrameFor(mFrames.FirstChild());
+
+  return aSummaryFrame == firstChild;
+}
diff --git a/layout/generic/DetailsFrame.h b/layout/generic/DetailsFrame.h
index 1eb4ea87b..4ae177f16 100644
--- a/layout/generic/DetailsFrame.h
+++ b/layout/generic/DetailsFrame.h
@@ -54,6 +54,12 @@ public:
 
   void AppendAnonymousContentTo(nsTArray<nsIContent*>& aElements,
                                 uint32_t aFilter) override;
+  // Returns true if |aSummaryFrame| is the main summary (i.e. the first child
+  // of this details frame).
+  // This function is used when the summary element is removed from the parent
+  // details element since at that moment the summary element has been already
+  // removed from the details element children.
+  bool HasMainSummaryFrame(nsIFrame* aSummaryFrame);
 
 private:
   nsCOMPtr<nsIContent> mDefaultSummary;