--- a/layout/style/nsStyleContext.h
+++ b/layout/style/nsStyleContext.h
@@ -123,23 +123,16 @@ public:
     --mFrameRefCnt;
   }
 
   uint32_t FrameRefCnt() const {
     return mFrameRefCnt;
   }
 #endif
 
-  bool HasSingleReference() const {
-    NS_ASSERTION(mRefCnt != 0,
-                 "do not call HasSingleReference on a newly created "
-                 "nsStyleContext with no references yet");
-    return mRefCnt == 1;
-  }
-
   nsPresContext* PresContext() const { return mRuleNode->PresContext(); }
 
   nsStyleContext* GetParent() const { return mParent; }
 
   nsIAtom* GetPseudo() const { return mPseudoTag; }
   mozilla::CSSPseudoElementType GetPseudoType() const {
     return static_cast<mozilla::CSSPseudoElementType>(
              mBits >> NS_STYLE_CONTEXT_TYPE_SHIFT);