diff --git a/content/canvas/src/nsCanvasRenderingContext2D.cpp b/content/canvas/src/nsCanvasRenderingContext2D.cpp
index 81c48d0fcb9e..dcb639c128bb 100644
--- a/content/canvas/src/nsCanvasRenderingContext2D.cpp
+++ b/content/canvas/src/nsCanvasRenderingContext2D.cpp
@@ -297,7 +297,6 @@ NS_INTERFACE_MAP_BEGIN(nsTextMetrics)
 NS_INTERFACE_MAP_END
 
 struct nsCanvasBidiProcessor;
-class CanvasRenderingContext2DUserData;
 
 /**
  ** nsCanvasRenderingContext2D
@@ -378,7 +377,6 @@ public:
         nsRefPtr<gfxPath> mPath;
     };
     friend class PathAutoSaveRestore;
-    friend class CanvasRenderingContext2DUserData;
 
 protected:
     nsresult GetImageDataArray(JSContext* aCx, int32_t aX, int32_t aY,
@@ -441,8 +439,6 @@ protected:
 
     // the canvas element we're a context of
     nsCOMPtr<nsIDOMHTMLCanvasElement> mCanvasElement;
-    nsTArray<CanvasRenderingContext2DUserData*> mUserDatas;
-
     nsHTMLCanvasElement *HTMLCanvasElement() {
         return static_cast<nsHTMLCanvasElement*>(mCanvasElement.get());
     }
@@ -759,40 +755,6 @@ protected:
     friend struct nsCanvasBidiProcessor;
 };
 
-class CanvasRenderingContext2DUserData : public LayerUserData {
-public:
-    CanvasRenderingContext2DUserData(nsCanvasRenderingContext2D *aContext)
-        : mContext(aContext)
-    {
-        aContext->mUserDatas.AppendElement(this);
-    }
-    ~CanvasRenderingContext2DUserData()
-    {
-        if (mContext) {
-            mContext->mUserDatas.RemoveElement(this);
-        }
-    }
-    static void DidTransactionCallback(void* aData)
-    {
-        CanvasRenderingContext2DUserData* self =
-            static_cast<CanvasRenderingContext2DUserData*>(aData);
-        if (self->mContext) {
-            self->mContext->MarkContextClean();
-        }
-    }
-    bool IsForContext(nsCanvasRenderingContext2D *aContext)
-    {
-        return mContext == aContext;
-    }
-    void Forget()
-    {
-        mContext = nsnull;
-    }
-
-private:
-    nsCanvasRenderingContext2D *mContext;
-};
-
 NS_IMPL_CYCLE_COLLECTING_ADDREF(nsCanvasRenderingContext2D)
 NS_IMPL_CYCLE_COLLECTING_RELEASE(nsCanvasRenderingContext2D)
 
@@ -848,10 +810,6 @@ nsCanvasRenderingContext2D::nsCanvasRenderingContext2D()
 nsCanvasRenderingContext2D::~nsCanvasRenderingContext2D()
 {
     Reset();
-    // Drop references from all CanvasRenderingContext2DUserDatas to this context
-    for (PRUint32 i = 0; i < mUserDatas.Length(); ++i) {
-        mUserDatas[i]->Forget();
-    }
     sNumLivingContexts--;
     if (!sNumLivingContexts) {
         delete[] sUnpremultiplyTable;
@@ -4202,6 +4160,19 @@ nsCanvasRenderingContext2D::SetMozImageSmoothingEnabled(bool val)
 
 static PRUint8 g2DContextLayerUserData;
 
+class CanvasRenderingContext2DUserData : public LayerUserData {
+public:
+  CanvasRenderingContext2DUserData(nsHTMLCanvasElement *aContent)
+    : mContent(aContent) {}
+  static void DidTransactionCallback(void* aData)
+  {
+    static_cast<CanvasRenderingContext2DUserData*>(aData)->mContent->MarkContextClean();
+  }
+
+private:
+  nsRefPtr<nsHTMLCanvasElement> mContent;
+};
+
 already_AddRefed<CanvasLayer>
 nsCanvasRenderingContext2D::GetCanvasLayer(nsDisplayListBuilder* aBuilder,
                                            CanvasLayer *aOldLayer,
@@ -4210,14 +4181,10 @@ nsCanvasRenderingContext2D::GetCanvasLayer(nsDisplayListBuilder* aBuilder,
     if (!EnsureSurface()) 
         return nsnull;
 
-    if (!mResetLayer && aOldLayer) {
-        CanvasRenderingContext2DUserData* userData =
-            static_cast<CanvasRenderingContext2DUserData*>(
-                    aOldLayer->GetUserData(&g2DContextLayerUserData));
-        if (userData && userData->IsForContext(this)) {
-            NS_ADDREF(aOldLayer);
-            return aOldLayer;
-        }
+    if (!mResetLayer && aOldLayer &&
+        aOldLayer->HasUserData(&g2DContextLayerUserData)) {
+        NS_ADDREF(aOldLayer);
+        return aOldLayer;
     }
 
     nsRefPtr<CanvasLayer> canvasLayer = aManager->CreateCanvasLayer();
@@ -4239,7 +4206,7 @@ nsCanvasRenderingContext2D::GetCanvasLayer(nsDisplayListBuilder* aBuilder,
       // releasing the reference to the element.
       // The userData will receive DidTransactionCallbacks, which flush the
       // the invalidation state to indicate that the canvas is up to date.
-      userData = new CanvasRenderingContext2DUserData(this);
+      userData = new CanvasRenderingContext2DUserData(HTMLCanvasElement());
       canvasLayer->SetDidTransactionCallback(
               CanvasRenderingContext2DUserData::DidTransactionCallback, userData);
     }
diff --git a/content/canvas/src/nsCanvasRenderingContext2DAzure.cpp b/content/canvas/src/nsCanvasRenderingContext2DAzure.cpp
index 72829a344edd..a0d1cdd28743 100644
--- a/content/canvas/src/nsCanvasRenderingContext2DAzure.cpp
+++ b/content/canvas/src/nsCanvasRenderingContext2DAzure.cpp
@@ -351,7 +351,6 @@ NS_INTERFACE_MAP_BEGIN(nsTextMetricsAzure)
 NS_INTERFACE_MAP_END
 
 struct nsCanvasBidiProcessorAzure;
-class CanvasRenderingContext2DUserData;
 
 // Cap sigma to avoid overly large temp surfaces.
 static const Float SIGMA_MAX = 100;
@@ -417,8 +416,6 @@ public:
   nsresult LineTo(const Point& aPoint);
   nsresult BezierTo(const Point& aCP1, const Point& aCP2, const Point& aCP3);
 
-  friend class CanvasRenderingContext2DUserData;
-
 protected:
   nsresult GetImageDataArray(JSContext* aCx, int32_t aX, int32_t aY,
                              uint32_t aWidth, uint32_t aHeight,
@@ -504,8 +501,6 @@ protected:
   // the canvas element we're a context of
   nsCOMPtr<nsIDOMHTMLCanvasElement> mCanvasElement;
 
-  nsTArray<CanvasRenderingContext2DUserData*> mUserDatas;
-
   // If mCanvasElement is not provided, then a docshell is
   nsCOMPtr<nsIDocShell> mDocShell;
 
@@ -938,40 +933,6 @@ protected:
   friend struct nsCanvasBidiProcessorAzure;
 };
 
-class CanvasRenderingContext2DUserData : public LayerUserData {
-public:
-  CanvasRenderingContext2DUserData(nsCanvasRenderingContext2DAzure *aContext)
-    : mContext(aContext)
-  {
-    aContext->mUserDatas.AppendElement(this);
-  }
-  ~CanvasRenderingContext2DUserData()
-  {
-    if (mContext) {
-      mContext->mUserDatas.RemoveElement(this);
-    }
-  }
-  static void DidTransactionCallback(void* aData)
-  {
-    CanvasRenderingContext2DUserData* self =
-      static_cast<CanvasRenderingContext2DUserData*>(aData);
-    if (self->mContext) {
-      self->mContext->MarkContextClean();
-    }
-  }
-  bool IsForContext(nsCanvasRenderingContext2DAzure *aContext)
-  {
-    return mContext == aContext;
-  }
-  void Forget()
-  {
-    mContext = nsnull;
-  }
-
-private:
-  nsCanvasRenderingContext2DAzure *mContext;
-};
-
 NS_IMPL_CYCLE_COLLECTING_ADDREF(nsCanvasRenderingContext2DAzure)
 NS_IMPL_CYCLE_COLLECTING_RELEASE(nsCanvasRenderingContext2DAzure)
 
@@ -1039,10 +1000,6 @@ nsCanvasRenderingContext2DAzure::nsCanvasRenderingContext2DAzure()
 nsCanvasRenderingContext2DAzure::~nsCanvasRenderingContext2DAzure()
 {
   Reset();
-  // Drop references from all CanvasRenderingContext2DUserDatas to this context
-  for (PRUint32 i = 0; i < mUserDatas.Length(); ++i) {
-    mUserDatas[i]->Forget();
-  }
   sNumLivingContexts--;
   if (!sNumLivingContexts) {
     delete[] sUnpremultiplyTable;
@@ -4388,6 +4345,19 @@ nsCanvasRenderingContext2DAzure::SetMozImageSmoothingEnabled(bool val)
 
 static PRUint8 g2DContextLayerUserData;
 
+class CanvasRenderingContext2DUserData : public LayerUserData {
+public:
+  CanvasRenderingContext2DUserData(nsHTMLCanvasElement *aContent)
+    : mContent(aContent) {}
+  static void DidTransactionCallback(void* aData)
+  {
+    static_cast<CanvasRenderingContext2DUserData*>(aData)->mContent->MarkContextClean();
+  }
+
+private:
+  nsRefPtr<nsHTMLCanvasElement> mContent;
+};
+
 already_AddRefed<CanvasLayer>
 nsCanvasRenderingContext2DAzure::GetCanvasLayer(nsDisplayListBuilder* aBuilder,
                                            CanvasLayer *aOldLayer,
@@ -4401,20 +4371,16 @@ nsCanvasRenderingContext2DAzure::GetCanvasLayer(nsDisplayListBuilder* aBuilder,
     mTarget->Flush();
   }
 
-  if (!mResetLayer && aOldLayer) {
-    CanvasRenderingContext2DUserData* userData =
-      static_cast<CanvasRenderingContext2DUserData*>(
-        aOldLayer->GetUserData(&g2DContextLayerUserData));
-    if (userData && userData->IsForContext(this)) {
+  if (!mResetLayer && aOldLayer &&
+      aOldLayer->HasUserData(&g2DContextLayerUserData)) {
       NS_ADDREF(aOldLayer);
       return aOldLayer;
-    }
   }
 
   nsRefPtr<CanvasLayer> canvasLayer = aManager->CreateCanvasLayer();
   if (!canvasLayer) {
-    NS_WARNING("CreateCanvasLayer returned null!");
-    return nsnull;
+      NS_WARNING("CreateCanvasLayer returned null!");
+      return nsnull;
   }
   CanvasRenderingContext2DUserData *userData = nsnull;
   if (aBuilder->IsPaintingToWindow()) {
@@ -4430,7 +4396,7 @@ nsCanvasRenderingContext2DAzure::GetCanvasLayer(nsDisplayListBuilder* aBuilder,
     // releasing the reference to the element.
     // The userData will receive DidTransactionCallbacks, which flush the
     // the invalidation state to indicate that the canvas is up to date.
-    userData = new CanvasRenderingContext2DUserData(this);
+    userData = new CanvasRenderingContext2DUserData(HTMLCanvasElement());
     canvasLayer->SetDidTransactionCallback(
             CanvasRenderingContext2DUserData::DidTransactionCallback, userData);
   }