diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index 359be08132ec..da26b2cbe4eb 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -9797,7 +9797,7 @@ nsIDocument::SetNavigationTiming(nsDOMNavigationTiming* aTiming)
 }
 
 Element*
-nsDocument::FindImageMap(const nsAString& aUseMapValue)
+nsIDocument::FindImageMap(const nsAString& aUseMapValue)
 {
   if (aUseMapValue.IsEmpty()) {
     return nullptr;
diff --git a/dom/base/nsDocument.h b/dom/base/nsDocument.h
index 12c7dec9113a..c4e8b61d0ec0 100644
--- a/dom/base/nsDocument.h
+++ b/dom/base/nsDocument.h
@@ -658,8 +658,6 @@ public:
 
   virtual nsresult GetStateObject(nsIVariant** aResult) override;
 
-  virtual Element* FindImageMap(const nsAString& aNormalizedMapName) override;
-
   // Returns the size of the mBlockedTrackingNodes array. (nsIDocument.h)
   //
   // This array contains nodes that have been blocked to prevent
@@ -867,8 +865,6 @@ private:
   // Set if we've found a URL for the current picture
   nsString mPreloadPictureFoundSource;
 
-  RefPtr<nsContentList> mImageMaps;
-
   nsCString mScrollToRef;
   uint8_t mScrolledToRefAlready : 1;
   uint8_t mChangeScrollPosWhenScrollingToRef : 1;
diff --git a/dom/base/nsIDocument.h b/dom/base/nsIDocument.h
index 034ea97fdc5b..8f5f63371ccc 100644
--- a/dom/base/nsIDocument.h
+++ b/dom/base/nsIDocument.h
@@ -2798,7 +2798,7 @@ public:
 
   void SetNavigationTiming(nsDOMNavigationTiming* aTiming);
 
-  virtual Element* FindImageMap(const nsAString& aNormalizedMapName) = 0;
+  Element* FindImageMap(const nsAString& aNormalizedMapName);
 
   // Add aLink to the set of links that need their status resolved.
   void RegisterPendingLinkUpdate(mozilla::dom::Link* aLink);
@@ -4054,10 +4054,13 @@ protected:
 
   RefPtr<mozilla::dom::DOMImplementation> mDOMImplementation;
 
+  RefPtr<nsContentList> mImageMaps;
+
 public:
   js::ExpandoAndGeneration mExpandoAndGeneration;
 
 protected:
+
   nsTArray<RefPtr<mozilla::StyleSheet>> mOnDemandBuiltInUASheets;
   nsTArray<RefPtr<mozilla::StyleSheet>> mAdditionalSheets[AdditionalSheetTypeCount];