diff --git a/layout/base/nsDisplayList.cpp b/layout/base/nsDisplayList.cpp
index efcfb8bdd4ef..30a974ca11ce 100644
--- a/layout/base/nsDisplayList.cpp
+++ b/layout/base/nsDisplayList.cpp
@@ -2528,6 +2528,17 @@ nsDisplayFixedPosition::BuildLayer(nsDisplayListBuilder* aBuilder,
   return layer.forget();
 }
 
+bool nsDisplayFixedPosition::TryMerge(nsDisplayListBuilder* aBuilder, nsDisplayItem* aItem) {
+  if (aItem->GetType() != TYPE_FIXED_POSITION)
+    return false;
+  // Items with the same fixed position frame can be merged.
+  nsDisplayFixedPosition* other = static_cast<nsDisplayFixedPosition*>(aItem);
+  if (other->mFixedPosFrame != mFixedPosFrame)
+    return false;
+  MergeFromTrackingMergedFrames(other);
+  return true;
+}
+
 nsDisplayScrollLayer::nsDisplayScrollLayer(nsDisplayListBuilder* aBuilder,
                                            nsDisplayList* aList,
                                            nsIFrame* aForFrame,
diff --git a/layout/base/nsDisplayList.h b/layout/base/nsDisplayList.h
index df3471911737..750811e114c3 100644
--- a/layout/base/nsDisplayList.h
+++ b/layout/base/nsDisplayList.h
@@ -1948,6 +1948,8 @@ public:
   {
     return mozilla::LAYER_ACTIVE;
   }
+  virtual bool TryMerge(nsDisplayListBuilder* aBuilder, nsDisplayItem* aItem);
+
   NS_DISPLAY_DECL_NAME("FixedPosition", TYPE_FIXED_POSITION)
 
 protected: