--- a/layout/generic/DetailsFrame.cpp
+++ b/layout/generic/DetailsFrame.cpp
@@ -23,16 +23,18 @@ NS_QUERYFRAME_HEAD(DetailsFrame)
 NS_QUERYFRAME_TAIL_INHERITING(nsBlockFrame)
 
 nsBlockFrame*
 NS_NewDetailsFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
 {
   return new (aPresShell) DetailsFrame(aContext);
 }
 
+namespace mozilla {
+
 DetailsFrame::DetailsFrame(nsStyleContext* aContext)
   : nsBlockFrame(aContext)
 {
 }
 
 DetailsFrame::~DetailsFrame()
 {
 }
@@ -124,8 +126,10 @@ DetailsFrame::CreateAnonymousContent(nsT
 void
 DetailsFrame::AppendAnonymousContentTo(nsTArray<nsIContent*>& aElements,
                                        uint32_t aFilter)
 {
   if (mDefaultSummary) {
     aElements.AppendElement(mDefaultSummary);
   }
 }
+
+} // namespace mozilla

--- a/layout/generic/DetailsFrame.h
+++ b/layout/generic/DetailsFrame.h
@@ -8,16 +8,18 @@
 #define DetailsFrame_h
 
 #include "nsBlockFrame.h"
 #include "nsIAnonymousContentCreator.h"
 
 class nsContainerFrame;
 class nsStyleContext;
 
+namespace mozilla {
+
 // DetailsFrame is generated by HTMLDetailsElement. See
 // nsCSSFrameConstructor::ConstructDetailsFrame for the structure of a
 // DetailsFrame.
 //
 class DetailsFrame final : public nsBlockFrame
                          , public nsIAnonymousContentCreator
 {
 public:
@@ -54,9 +56,11 @@ public:
 
   void AppendAnonymousContentTo(nsTArray<nsIContent*>& aElements,
                                 uint32_t aFilter) override;
 
 private:
   nsCOMPtr<nsIContent> mDefaultSummary;
 };
 
+} // namespace mozilla
+
 #endif // DetailsFrame_h