diff --git a/content/canvas/public/DocumentRendererChild.h b/content/canvas/public/DocumentRendererChild.h
index e70a9e4de500..0cdc478e581d 100644
--- a/content/canvas/public/DocumentRendererChild.h
+++ b/content/canvas/public/DocumentRendererChild.h
@@ -6,7 +6,6 @@
 #define mozilla_dom_DocumentRendererChild
 
 #include "mozilla/ipc/PDocumentRendererChild.h"
-#include "nsICanvasRenderingContextInternal.h"
 #include "nsString.h"
 #include "gfxContext.h"
 
diff --git a/content/canvas/public/DocumentRendererParent.h b/content/canvas/public/DocumentRendererParent.h
index 394bcc9b15b8..9e332faeb474 100644
--- a/content/canvas/public/DocumentRendererParent.h
+++ b/content/canvas/public/DocumentRendererParent.h
@@ -6,11 +6,12 @@
 #define mozilla_dom_DocumentRendererParent
 
 #include "mozilla/ipc/PDocumentRendererParent.h"
-#include "nsICanvasRenderingContextInternal.h"
 #include "nsCOMPtr.h"
 #include "nsString.h"
 #include "gfxContext.h"
 
+class nsICanvasRenderingContextInternal;
+
 namespace mozilla {
 namespace ipc {
 
diff --git a/content/canvas/public/nsICanvasRenderingContextInternal.h b/content/canvas/public/nsICanvasRenderingContextInternal.h
index 91f8fb9c7870..ab66374adc07 100644
--- a/content/canvas/public/nsICanvasRenderingContextInternal.h
+++ b/content/canvas/public/nsICanvasRenderingContextInternal.h
@@ -9,14 +9,14 @@
 #include "nsISupports.h"
 #include "nsIInputStream.h"
 #include "nsIDocShell.h"
+#include "nsHTMLCanvasElement.h"
 #include "gfxPattern.h"
 #include "mozilla/RefPtr.h"
 
 #define NS_ICANVASRENDERINGCONTEXTINTERNAL_IID \
-{ 0xffb42d3c, 0x8281, 0x44c8, \
-  { 0xac, 0xba, 0x73, 0x15, 0x31, 0xaa, 0xe5, 0x07 } }
+{ 0x8b8da863, 0xd151, 0x4014, \
+  { 0x8b, 0xdc, 0x62, 0xb5, 0x0d, 0xc0, 0x2b, 0x62 } }
 
-class nsHTMLCanvasElement;
 class gfxContext;
 class gfxASurface;
 class nsIPropertyBag;
@@ -46,9 +46,10 @@ public:
     RenderFlagPremultAlpha = 0x1
   };
 
-  // This method should NOT hold a ref to aParentCanvas; it will be called
-  // with nsnull when the element is going away.
-  NS_IMETHOD SetCanvasElement(nsHTMLCanvasElement* aParentCanvas) = 0;
+  void SetCanvasElement(nsHTMLCanvasElement* aParentCanvas)
+  {
+    mCanvasElement = aParentCanvas;
+  }
 
   // Sets the dimensions of the canvas, in pixels.  Called
   // whenever the size of the element changes.
@@ -119,6 +120,9 @@ public:
   // anything into this canvas before changing the shmem state, it will be
   // lost.
   NS_IMETHOD SetIsIPC(bool isIPC) = 0;
+
+protected:
+  nsRefPtr<nsHTMLCanvasElement> mCanvasElement;
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(nsICanvasRenderingContextInternal,
diff --git a/content/canvas/src/DocumentRendererChild.cpp b/content/canvas/src/DocumentRendererChild.cpp
index f742e0ac571d..02856a2b4bd6 100644
--- a/content/canvas/src/DocumentRendererChild.cpp
+++ b/content/canvas/src/DocumentRendererChild.cpp
@@ -11,6 +11,7 @@
 #include "nsPIDOMWindow.h"
 #include "nsIDOMWindow.h"
 #include "nsIDOMDocument.h"
+#include "nsIDocShell.h"
 #include "nsIDocShellTreeNode.h"
 #include "nsIDocShellTreeItem.h"
 #include "nsIDocument.h"
diff --git a/content/canvas/src/DocumentRendererParent.cpp b/content/canvas/src/DocumentRendererParent.cpp
index 622943520f95..13af5c9799eb 100644
--- a/content/canvas/src/DocumentRendererParent.cpp
+++ b/content/canvas/src/DocumentRendererParent.cpp
@@ -5,6 +5,7 @@
 #include "mozilla/ipc/DocumentRendererParent.h"
 #include "gfxImageSurface.h"
 #include "gfxPattern.h"
+#include "nsICanvasRenderingContextInternal.h"
 
 using namespace mozilla::ipc;
 
diff --git a/content/canvas/src/WebGLContext.cpp b/content/canvas/src/WebGLContext.cpp
index ec7ac6ec0e43..ff3bb53c95e0 100644
--- a/content/canvas/src/WebGLContext.cpp
+++ b/content/canvas/src/WebGLContext.cpp
@@ -73,8 +73,7 @@ NS_NewCanvasRenderingContextWebGL(nsIDOMWebGLRenderingContext** aResult)
 }
 
 WebGLContext::WebGLContext()
-    : mCanvasElement(nsnull),
-      gl(nsnull)
+    : gl(nsnull)
 {
     SetIsDOMBinding();
     mEnabledExtensions.SetLength(WebGLExtensionID_Max);
@@ -243,10 +242,10 @@ WebGLContext::Invalidate()
     if (!mCanvasElement)
         return;
 
-    nsSVGEffects::InvalidateDirectRenderingObservers(HTMLCanvasElement());
+    nsSVGEffects::InvalidateDirectRenderingObservers(mCanvasElement);
 
     mInvalidated = true;
-    HTMLCanvasElement()->InvalidateCanvasContent(nsnull);
+    mCanvasElement->InvalidateCanvasContent(nsnull);
 }
 
 /* readonly attribute nsIDOMHTMLCanvasElement canvas; */
@@ -262,14 +261,6 @@ WebGLContext::GetCanvas(nsIDOMHTMLCanvasElement **canvas)
 // nsICanvasRenderingContextInternal
 //
 
-NS_IMETHODIMP
-WebGLContext::SetCanvasElement(nsHTMLCanvasElement* aParentCanvas)
-{
-    mCanvasElement = aParentCanvas;
-
-    return NS_OK;
-}
-
 static bool
 GetBoolFromPropertyBag(nsIPropertyBag *bag, const char *propName, bool *boolResult)
 {
@@ -332,7 +323,7 @@ WebGLContext::SetDimensions(PRInt32 width, PRInt32 height)
     /*** early success return cases ***/
   
     if (mCanvasElement) {
-        HTMLCanvasElement()->InvalidateCanvas();
+        mCanvasElement->InvalidateCanvas();
     }
 
     if (gl && mWidth == width && mHeight == height)
@@ -727,7 +718,7 @@ WebGLContext::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 WebGLContextUserData(HTMLCanvasElement());
+      userData = new WebGLContextUserData(mCanvasElement);
       canvasLayer->SetDidTransactionCallback(
               WebGLContextUserData::DidTransactionCallback, userData);
     }
@@ -1066,7 +1057,7 @@ WebGLContext::Notify(nsITimer* timer)
 {
     TerminateContextLossTimer();
 
-    if (!HTMLCanvasElement()) {
+    if (!mCanvasElement) {
         // the canvas is gone. That happens when the page was closed before we got
         // this timer event. In this case, there's nothing to do here, just don't crash.
         return NS_OK;
@@ -1076,8 +1067,8 @@ WebGLContext::Notify(nsITimer* timer)
     // that now.
     if (mContextStatus == ContextLostAwaitingEvent) {
         bool defaultAction;
-        nsContentUtils::DispatchTrustedEvent(HTMLCanvasElement()->OwnerDoc(),
-                                             (nsIDOMHTMLCanvasElement*) HTMLCanvasElement(),
+        nsContentUtils::DispatchTrustedEvent(mCanvasElement->OwnerDoc(),
+                                             static_cast<nsIDOMHTMLCanvasElement*>(mCanvasElement),
                                              NS_LITERAL_STRING("webglcontextlost"),
                                              true,
                                              true,
@@ -1105,8 +1096,8 @@ WebGLContext::Notify(nsITimer* timer)
             return NS_OK;
         }
         mContextStatus = ContextStable;
-        nsContentUtils::DispatchTrustedEvent(HTMLCanvasElement()->OwnerDoc(),
-                                             (nsIDOMHTMLCanvasElement*) HTMLCanvasElement(),
+        nsContentUtils::DispatchTrustedEvent(mCanvasElement->OwnerDoc(),
+                                             static_cast<nsIDOMHTMLCanvasElement*>(mCanvasElement),
                                              NS_LITERAL_STRING("webglcontextrestored"),
                                              true,
                                              true);
@@ -1215,7 +1206,7 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(WebGLContext)
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(WebGLContext)
-  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NSCOMPTR(mCanvasElement)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NSCOMPTR_AMBIGUOUS(mCanvasElement, nsINode)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NSTARRAY_OF_NSCOMPTR(mEnabledExtensions)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
diff --git a/content/canvas/src/WebGLContext.h b/content/canvas/src/WebGLContext.h
index cb773b7e6ca9..8e8f119bd7c1 100644
--- a/content/canvas/src/WebGLContext.h
+++ b/content/canvas/src/WebGLContext.h
@@ -483,7 +483,7 @@ public:
                                                            nsIDOMWebGLRenderingContext)
 
     nsINode* GetParentObject() {
-        return HTMLCanvasElement();
+        return mCanvasElement;
     }
 
     virtual JSObject* WrapObject(JSContext *cx, JSObject *scope,
@@ -494,11 +494,6 @@ public:
     NS_DECL_NSITIMERCALLBACK
 
     // nsICanvasRenderingContextInternal
-    NS_IMETHOD SetCanvasElement(nsHTMLCanvasElement* aParentCanvas);
-    nsHTMLCanvasElement* HTMLCanvasElement() const {
-        return static_cast<nsHTMLCanvasElement*>(mCanvasElement.get());
-    }
-
     NS_IMETHOD SetDimensions(PRInt32 width, PRInt32 height);
     NS_IMETHOD InitializeWithSurface(nsIDocShell *docShell, gfxASurface *surface, PRInt32 width, PRInt32 height)
         { return NS_ERROR_NOT_IMPLEMENTED; }
@@ -619,7 +614,7 @@ public:
 
     // WebIDL WebGLRenderingContext API
     nsHTMLCanvasElement* GetCanvas() const {
-        return HTMLCanvasElement();
+        return mCanvasElement;
     }
     WebGLsizei GetDrawingBufferWidth() const {
         if (!IsContextStable())
@@ -1107,8 +1102,6 @@ protected:
         return ((x + y - 1) / y) * y;
     }
 
-    nsCOMPtr<nsIDOMHTMLCanvasElement> mCanvasElement;
-
     nsRefPtr<gl::GLContext> gl;
 
     CheckedUint32 mGeneration;
diff --git a/content/canvas/src/WebGLContextGL.cpp b/content/canvas/src/WebGLContextGL.cpp
index 611f42b19004..625024979a16 100644
--- a/content/canvas/src/WebGLContextGL.cpp
+++ b/content/canvas/src/WebGLContextGL.cpp
@@ -3841,7 +3841,7 @@ WebGLContext::ReadPixels(WebGLint x, WebGLint y, WebGLsizei width,
         return;
     }
 
-    if (HTMLCanvasElement()->IsWriteOnly() && !nsContentUtils::IsCallerTrustedForRead()) {
+    if (mCanvasElement->IsWriteOnly() && !nsContentUtils::IsCallerTrustedForRead()) {
         GenerateWarning("readPixels: Not allowed");
         return rv.Throw(NS_ERROR_DOM_SECURITY_ERR);
     }
@@ -4343,7 +4343,7 @@ WebGLContext::SurfaceFromElementResultToImageSurface(nsLayoutUtils::SurfaceFromE
     // validated for cross-domain use.
     if (!res.mCORSUsed) {
         bool subsumes;
-        nsresult rv = HTMLCanvasElement()->NodePrincipal()->Subsumes(res.mPrincipal, &subsumes);
+        nsresult rv = mCanvasElement->NodePrincipal()->Subsumes(res.mPrincipal, &subsumes);
         if (NS_FAILED(rv) || !subsumes) {
             GenerateWarning("It is forbidden to load a WebGL texture from a cross-domain element that has not been validated with CORS. "
                                 "See https://developer.mozilla.org/en/WebGL/Cross-Domain_Textures");
diff --git a/content/canvas/src/nsCanvasRenderingContext2D.cpp b/content/canvas/src/nsCanvasRenderingContext2D.cpp
index f4e43de333ac..05f77b03bf9b 100644
--- a/content/canvas/src/nsCanvasRenderingContext2D.cpp
+++ b/content/canvas/src/nsCanvasRenderingContext2D.cpp
@@ -317,7 +317,6 @@ public:
     nsresult Redraw();
 
     // nsICanvasRenderingContextInternal
-    NS_IMETHOD SetCanvasElement(nsHTMLCanvasElement* aParentCanvas);
     NS_IMETHOD SetDimensions(PRInt32 width, PRInt32 height);
     void Initialize(nsIDocShell *shell, PRInt32 width, PRInt32 height);
     NS_IMETHOD InitializeWithSurface(nsIDocShell *shell, gfxASurface *surface, PRInt32 width, PRInt32 height);
@@ -445,12 +444,6 @@ protected:
     bool mResetLayer;
     bool mIPC;
 
-    // the canvas element we're a context of
-    nsCOMPtr<nsIDOMHTMLCanvasElement> mCanvasElement;
-    nsHTMLCanvasElement *HTMLCanvasElement() {
-        return static_cast<nsHTMLCanvasElement*>(mCanvasElement.get());
-    }
-
     // Initialize the Thebes rendering context
     void CreateThebes();
 
@@ -771,7 +764,7 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsCanvasRenderingContext2D)
   NS_IMPL_CYCLE_COLLECTION_UNLINK_NSCOMPTR(mCanvasElement)
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(nsCanvasRenderingContext2D)
-  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NSCOMPTR(mCanvasElement)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NSCOMPTR_AMBIGUOUS(mCanvasElement, nsINode)
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
 DOMCI_DATA(CanvasRenderingContext2D, nsCanvasRenderingContext2D)
@@ -807,7 +800,6 @@ NS_NewCanvasRenderingContext2DThebes(nsIDOMCanvasRenderingContext2D** aResult)
 nsCanvasRenderingContext2D::nsCanvasRenderingContext2D()
     : mValid(false), mZero(false), mOpaque(false), mResetLayer(true)
     , mIPC(false)
-    , mCanvasElement(nsnull)
     , mSaveCount(0), mIsEntireFrameInvalid(false)
     , mPredictManyRedrawCalls(false), mHasPath(false), mInvalidateCount(0)
     , mLastStyle(STYLE_MAX), mStyleStack(20)
@@ -831,9 +823,9 @@ bool
 nsCanvasRenderingContext2D::ParseColor(const nsAString& aString,
                                        nscolor* aColor)
 {
-    nsIDocument* document = HTMLCanvasElement()
-                             ? HTMLCanvasElement()->OwnerDoc()
-                             : nsnull;
+    nsIDocument* document = mCanvasElement
+                            ? mCanvasElement->OwnerDoc()
+                            : nsnull;
 
     // Pass the CSS Loader object to the parser, to allow parser error
     // reports to include the outer window ID.
@@ -845,10 +837,10 @@ nsCanvasRenderingContext2D::ParseColor(const nsAString& aString,
 
     nsIPresShell* presShell = GetPresShell();
     nsRefPtr<nsStyleContext> parentContext;
-    if (HTMLCanvasElement() && HTMLCanvasElement()->IsInDoc()) {
+    if (mCanvasElement && mCanvasElement->IsInDoc()) {
         // Inherit from the canvas element.
         parentContext = nsComputedDOMStyle::GetStyleContextForElement(
-            HTMLCanvasElement(), nsnull, presShell);
+            mCanvasElement, nsnull, presShell);
     }
 
     unused << nsRuleNode::ComputeColor(
@@ -861,7 +853,7 @@ nsresult
 nsCanvasRenderingContext2D::Reset()
 {
     if (mCanvasElement) {
-        HTMLCanvasElement()->InvalidateCanvas();
+        mCanvasElement->InvalidateCanvas();
     }
 
     // only do this for non-docshell created contexts,
@@ -913,7 +905,7 @@ nsCanvasRenderingContext2D::SetStyleFromStringOrInterface(const nsAString& aStr,
     nsContentUtils::ReportToConsole(
         nsIScriptError::warningFlag,
         "Canvas",
-        mCanvasElement ? HTMLCanvasElement()->OwnerDoc() : nsnull,
+        mCanvasElement ? mCanvasElement->OwnerDoc() : nsnull,
         nsContentUtils::eDOM_PROPERTIES,
         "UnexpectedCanvasVariantStyle");
 
@@ -997,7 +989,7 @@ nsCanvasRenderingContext2D::ApplyStyle(Style aWhichStyle,
     nsCanvasPattern* pattern = CurrentState().patternStyles[aWhichStyle];
     if (pattern) {
         if (mCanvasElement)
-            CanvasUtils::DoDrawImageSecurityCheck(HTMLCanvasElement(),
+            CanvasUtils::DoDrawImageSecurityCheck(mCanvasElement,
                                                   pattern->Principal(),
                                                   pattern->GetForceWriteOnly(),
                                                   pattern->GetCORSUsed());
@@ -1038,9 +1030,9 @@ nsCanvasRenderingContext2D::Redraw()
         return NS_OK;
     }
 
-    nsSVGEffects::InvalidateDirectRenderingObservers(HTMLCanvasElement());
+    nsSVGEffects::InvalidateDirectRenderingObservers(mCanvasElement);
 
-    HTMLCanvasElement()->InvalidateCanvasContent(nsnull);
+    mCanvasElement->InvalidateCanvasContent(nsnull);
 
     return NS_OK;
 }
@@ -1063,9 +1055,9 @@ nsCanvasRenderingContext2D::Redraw(const gfxRect& r)
         return NS_OK;
     }
 
-    nsSVGEffects::InvalidateDirectRenderingObservers(HTMLCanvasElement());
+    nsSVGEffects::InvalidateDirectRenderingObservers(mCanvasElement);
 
-    HTMLCanvasElement()->InvalidateCanvasContent(&r);
+    mCanvasElement->InvalidateCanvasContent(&r);
 
     return NS_OK;
 }
@@ -1377,14 +1369,6 @@ nsCanvasRenderingContext2D::GetImageFormat() const
 // nsCanvasRenderingContext2D impl
 //
 
-NS_IMETHODIMP
-nsCanvasRenderingContext2D::SetCanvasElement(nsHTMLCanvasElement* aCanvasElement)
-{
-    mCanvasElement = aCanvasElement;
-
-    return NS_OK;
-}
-
 NS_IMETHODIMP
 nsCanvasRenderingContext2D::GetCanvas(nsIDOMHTMLCanvasElement **canvas)
 {
@@ -2472,9 +2456,8 @@ nsCanvasRenderingContext2D::SetFont(const nsAString& font)
      * string is equal to the old one.
      */
 
-    nsCOMPtr<nsIContent> content = do_QueryInterface(mCanvasElement);
-    if (!content && !mDocShell) {
-        NS_WARNING("Canvas element must be an nsIContent and non-null or a docshell must be provided");
+    if (!mCanvasElement && !mDocShell) {
+        NS_WARNING("Canvas element must be non-null or a docshell must be provided");
         return NS_ERROR_FAILURE;
     }
 
@@ -2514,10 +2497,10 @@ nsCanvasRenderingContext2D::SetFont(const nsAString& font)
     // values (2em, bolder, etc.)
     nsRefPtr<nsStyleContext> parentContext;
 
-    if (content && content->IsInDoc()) {
+    if (mCanvasElement && mCanvasElement->IsInDoc()) {
         // inherit from the canvas element
         parentContext = nsComputedDOMStyle::GetStyleContextForElement(
-                content->AsElement(),
+                mCanvasElement,
                 nsnull,
                 presShell);
     } else {
@@ -2852,9 +2835,8 @@ nsCanvasRenderingContext2D::DrawOrMeasureText(const nsAString& aRawText,
     if (aMaxWidth < 0)
         return NS_ERROR_INVALID_ARG;
 
-    nsCOMPtr<nsIContent> content = do_QueryInterface(mCanvasElement);
-    if (!content && !mDocShell) {
-        NS_WARNING("Canvas element must be an nsIContent and non-null or a docshell must be provided");
+    if (!mCanvasElement && !mDocShell) {
+        NS_WARNING("Canvas element must be non-null or a docshell must be provided");
         return NS_ERROR_FAILURE;
     }
 
@@ -2871,10 +2853,10 @@ nsCanvasRenderingContext2D::DrawOrMeasureText(const nsAString& aRawText,
     // for now, default to ltr if not in doc
     bool isRTL = false;
 
-    if (content && content->IsInDoc()) {
+    if (mCanvasElement && mCanvasElement->IsInDoc()) {
         // try to find the closest context
         nsRefPtr<nsStyleContext> canvasStyle =
-            nsComputedDOMStyle::GetStyleContextForElement(content->AsElement(),
+            nsComputedDOMStyle::GetStyleContextForElement(mCanvasElement,
                                                           nsnull,
                                                           presShell);
         if (!canvasStyle)
@@ -3397,7 +3379,7 @@ nsCanvasRenderingContext2D::DrawImage(nsIDOMElement *imgElt, float a1,
     nsRefPtr<gfxPattern> pattern;
     gfxIntSize imgSize;
     nsRefPtr<gfxASurface> imgsurf =
-      CanvasImageCache::Lookup(imgElt, HTMLCanvasElement(), &imgSize);
+      CanvasImageCache::Lookup(imgElt, mCanvasElement, &imgSize);
 
     if (!imgsurf) {
         // The canvas spec says that drawImage should draw the first frame
@@ -3424,14 +3406,14 @@ nsCanvasRenderingContext2D::DrawImage(nsIDOMElement *imgElt, float a1,
         imgSize = res.mSize;
 
         if (mCanvasElement) {
-            CanvasUtils::DoDrawImageSecurityCheck(HTMLCanvasElement(),
+            CanvasUtils::DoDrawImageSecurityCheck(mCanvasElement,
                                                   res.mPrincipal,
                                                   res.mIsWriteOnly,
                                                   res.mCORSUsed);
         }
 
         if (res.mImageRequest) {
-            CanvasImageCache::NotifyDrawImage(imgElt, HTMLCanvasElement(),
+            CanvasImageCache::NotifyDrawImage(imgElt, mCanvasElement,
                                               res.mImageRequest, imgsurf, imgSize);
         }
     }
@@ -3834,8 +3816,7 @@ nsCanvasRenderingContext2D::GetImageData(double aSx, double aSy,
 
     // Check only if we have a canvas element; if we were created with a docshell,
     // then it's special internal use.
-    if (mCanvasElement &&
-        HTMLCanvasElement()->IsWriteOnly() &&
+    if (mCanvasElement && mCanvasElement->IsWriteOnly() &&
         !nsContentUtils::IsCallerTrustedForRead()) {
         // XXX ERRMSG we need to report an error to developers here! (bug 329026)
         return NS_ERROR_DOM_SECURITY_ERR;
@@ -4217,7 +4198,7 @@ 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(HTMLCanvasElement());
+      userData = new CanvasRenderingContext2DUserData(mCanvasElement);
       canvasLayer->SetDidTransactionCallback(
               CanvasRenderingContext2DUserData::DidTransactionCallback, userData);
     }
diff --git a/content/canvas/src/nsCanvasRenderingContext2DAzure.cpp b/content/canvas/src/nsCanvasRenderingContext2DAzure.cpp
index d8960d2a025f..619213cfd182 100644
--- a/content/canvas/src/nsCanvasRenderingContext2DAzure.cpp
+++ b/content/canvas/src/nsCanvasRenderingContext2DAzure.cpp
@@ -373,7 +373,6 @@ public:
   nsresult Redraw();
 
   // nsICanvasRenderingContextInternal
-  NS_IMETHOD SetCanvasElement(nsHTMLCanvasElement* aParentCanvas);
   NS_IMETHOD SetDimensions(PRInt32 width, PRInt32 height);
   NS_IMETHOD InitializeWithSurface(nsIDocShell *shell, gfxASurface *surface, PRInt32 width, PRInt32 height)
   { return NS_ERROR_NOT_IMPLEMENTED; }
@@ -482,10 +481,6 @@ protected:
     */
   SurfaceFormat GetSurfaceFormat() const;
 
-  nsHTMLCanvasElement *HTMLCanvasElement() {
-    return static_cast<nsHTMLCanvasElement*>(mCanvasElement.get());
-  }
-
   // Member vars
   PRInt32 mWidth, mHeight;
 
@@ -505,9 +500,6 @@ protected:
   // This is needed for drawing in drawAsyncXULElement
   bool mIPC;
 
-  // the canvas element we're a context of
-  nsCOMPtr<nsIDOMHTMLCanvasElement> mCanvasElement;
-
   // If mCanvasElement is not provided, then a docshell is
   nsCOMPtr<nsIDocShell> mDocShell;
 
@@ -784,7 +776,7 @@ protected:
                                 gradient->mRadius2, gradient->GetGradientStopsForTarget(aRT));
       } else if (state.patternStyles[aStyle]) {
         if (aCtx->mCanvasElement) {
-          CanvasUtils::DoDrawImageSecurityCheck(aCtx->HTMLCanvasElement(),
+          CanvasUtils::DoDrawImageSecurityCheck(aCtx->mCanvasElement,
                                                 state.patternStyles[aStyle]->mPrincipal,
                                                 state.patternStyles[aStyle]->mForceWriteOnly,
                                                 state.patternStyles[aStyle]->mCORSUsed);
@@ -948,7 +940,7 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsCanvasRenderingContext2DAzure)
   NS_IMPL_CYCLE_COLLECTION_UNLINK_NSCOMPTR(mCanvasElement)
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(nsCanvasRenderingContext2DAzure)
-  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NSCOMPTR(mCanvasElement)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NSCOMPTR_AMBIGUOUS(mCanvasElement, nsINode)
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
 // XXX
@@ -996,7 +988,6 @@ NS_NewCanvasRenderingContext2DAzure(nsIDOMCanvasRenderingContext2D** aResult)
 nsCanvasRenderingContext2DAzure::nsCanvasRenderingContext2DAzure()
   : mValid(false), mZero(false), mOpaque(false), mResetLayer(true)
   , mIPC(false)
-  , mCanvasElement(nsnull)
   , mIsEntireFrameInvalid(false)
   , mPredictManyRedrawCalls(false), mPathTransformWillUpdate(false)
   , mInvalidateCount(0)
@@ -1020,9 +1011,9 @@ bool
 nsCanvasRenderingContext2DAzure::ParseColor(const nsAString& aString,
                                             nscolor* aColor)
 {
-  nsIDocument* document = HTMLCanvasElement()
-                           ? HTMLCanvasElement()->OwnerDoc()
-                           : nsnull;
+  nsIDocument* document = mCanvasElement
+                          ? mCanvasElement->OwnerDoc()
+                          : nsnull;
 
   // Pass the CSS Loader object to the parser, to allow parser error
   // reports to include the outer window ID.
@@ -1034,10 +1025,10 @@ nsCanvasRenderingContext2DAzure::ParseColor(const nsAString& aString,
 
   nsIPresShell* presShell = GetPresShell();
   nsRefPtr<nsStyleContext> parentContext;
-  if (HTMLCanvasElement() && HTMLCanvasElement()->IsInDoc()) {
+  if (mCanvasElement && mCanvasElement->IsInDoc()) {
     // Inherit from the canvas element.
     parentContext = nsComputedDOMStyle::GetStyleContextForElement(
-      HTMLCanvasElement(), nsnull, presShell);
+      mCanvasElement, nsnull, presShell);
   }
 
   unused << nsRuleNode::ComputeColor(
@@ -1050,7 +1041,7 @@ nsresult
 nsCanvasRenderingContext2DAzure::Reset()
 {
   if (mCanvasElement) {
-    HTMLCanvasElement()->InvalidateCanvas();
+    mCanvasElement->InvalidateCanvas();
   }
 
   // only do this for non-docshell created contexts,
@@ -1103,7 +1094,7 @@ nsCanvasRenderingContext2DAzure::SetStyleFromStringOrInterface(const nsAString&
   nsContentUtils::ReportToConsole(
     nsIScriptError::warningFlag,
     "Canvas",
-    mCanvasElement ? HTMLCanvasElement()->OwnerDoc() : nsnull,
+    mCanvasElement ? mCanvasElement->OwnerDoc() : nsnull,
     nsContentUtils::eDOM_PROPERTIES,
     "UnexpectedCanvasVariantStyle");
 
@@ -1176,9 +1167,9 @@ nsCanvasRenderingContext2DAzure::Redraw()
       gfxPlatform::GetPlatform()->GetThebesSurfaceForDrawTarget(mTarget);
   mThebesSurface->MarkDirty();
 
-  nsSVGEffects::InvalidateDirectRenderingObservers(HTMLCanvasElement());
+  nsSVGEffects::InvalidateDirectRenderingObservers(mCanvasElement);
 
-  HTMLCanvasElement()->InvalidateCanvasContent(nsnull);
+  mCanvasElement->InvalidateCanvasContent(nsnull);
 
   return NS_OK;
 }
@@ -1208,10 +1199,10 @@ nsCanvasRenderingContext2DAzure::Redraw(const mgfx::Rect &r)
       gfxPlatform::GetPlatform()->GetThebesSurfaceForDrawTarget(mTarget);
   mThebesSurface->MarkDirty();
 
-  nsSVGEffects::InvalidateDirectRenderingObservers(HTMLCanvasElement());
+  nsSVGEffects::InvalidateDirectRenderingObservers(mCanvasElement);
 
   gfxRect tmpR = ThebesRect(r);
-  HTMLCanvasElement()->InvalidateCanvasContent(&tmpR);
+  mCanvasElement->InvalidateCanvasContent(&tmpR);
 
   return;
 }
@@ -1497,14 +1488,6 @@ nsCanvasRenderingContext2DAzure::GetSurfaceFormat() const
 // nsCanvasRenderingContext2DAzure impl
 //
 
-NS_IMETHODIMP
-nsCanvasRenderingContext2DAzure::SetCanvasElement(nsHTMLCanvasElement* aCanvasElement)
-{
-  mCanvasElement = aCanvasElement;
-
-  return NS_OK;
-}
-
 NS_IMETHODIMP
 nsCanvasRenderingContext2DAzure::GetCanvas(nsIDOMHTMLCanvasElement **canvas)
 {
@@ -2680,9 +2663,8 @@ nsCanvasRenderingContext2DAzure::SetFont(const nsAString& font)
     * string is equal to the old one.
     */
 
-  nsCOMPtr<nsIContent> content = do_QueryInterface(mCanvasElement);
-  if (!content && !mDocShell) {
-      NS_WARNING("Canvas element must be an nsIContent and non-null or a docshell must be provided");
+  if (!mCanvasElement && !mDocShell) {
+      NS_WARNING("Canvas element must be non-null or a docshell must be provided");
       return NS_ERROR_FAILURE;
   }
 
@@ -2725,10 +2707,10 @@ nsCanvasRenderingContext2DAzure::SetFont(const nsAString& font)
   // values (2em, bolder, etc.)
   nsRefPtr<nsStyleContext> parentContext;
 
-  if (content && content->IsInDoc()) {
+  if (mCanvasElement && mCanvasElement->IsInDoc()) {
       // inherit from the canvas element
       parentContext = nsComputedDOMStyle::GetStyleContextForElement(
-              content->AsElement(),
+              mCanvasElement,
               nsnull,
               presShell);
   } else {
@@ -3168,9 +3150,8 @@ nsCanvasRenderingContext2DAzure::DrawOrMeasureText(const nsAString& aRawText,
   if (aMaxWidth < 0)
     return NS_ERROR_INVALID_ARG;
 
-  nsCOMPtr<nsIContent> content = do_QueryInterface(mCanvasElement);
-  if (!content && !mDocShell) {
-      NS_WARNING("Canvas element must be an nsIContent and non-null or a docshell must be provided");
+  if (!mCanvasElement && !mDocShell) {
+    NS_WARNING("Canvas element must be non-null or a docshell must be provided");
     return NS_ERROR_FAILURE;
   }
 
@@ -3187,10 +3168,10 @@ nsCanvasRenderingContext2DAzure::DrawOrMeasureText(const nsAString& aRawText,
   // for now, default to ltr if not in doc
   bool isRTL = false;
 
-  if (content && content->IsInDoc()) {
+  if (mCanvasElement && mCanvasElement->IsInDoc()) {
     // try to find the closest context
     nsRefPtr<nsStyleContext> canvasStyle =
-      nsComputedDOMStyle::GetStyleContextForElement(content->AsElement(),
+      nsComputedDOMStyle::GetStyleContextForElement(mCanvasElement,
                                                     nsnull,
                                                     presShell);
     if (!canvasStyle) {
@@ -3629,7 +3610,7 @@ nsCanvasRenderingContext2DAzure::DrawImage(nsIDOMElement *imgElt, float a1,
 
       if (srcSurf && mCanvasElement) {
         // Do security check here.
-        CanvasUtils::DoDrawImageSecurityCheck(HTMLCanvasElement(),
+        CanvasUtils::DoDrawImageSecurityCheck(mCanvasElement,
                                               content->NodePrincipal(), canvas->IsWriteOnly(),
                                               false);
         imgSize = gfxIntSize(srcSurf->GetSize().width, srcSurf->GetSize().height);
@@ -3637,7 +3618,7 @@ nsCanvasRenderingContext2DAzure::DrawImage(nsIDOMElement *imgElt, float a1,
     }
   } else {
     gfxASurface* imgsurf =
-      CanvasImageCache::Lookup(imgElt, HTMLCanvasElement(), &imgSize);
+      CanvasImageCache::Lookup(imgElt, mCanvasElement, &imgSize);
     if (imgsurf) {
       srcSurf = gfxPlatform::GetPlatform()->GetSourceSurfaceForSurface(mTarget, imgsurf);
     }
@@ -3663,13 +3644,13 @@ nsCanvasRenderingContext2DAzure::DrawImage(nsIDOMElement *imgElt, float a1,
     imgSize = res.mSize;
 
     if (mCanvasElement) {
-      CanvasUtils::DoDrawImageSecurityCheck(HTMLCanvasElement(),
+      CanvasUtils::DoDrawImageSecurityCheck(mCanvasElement,
                                             res.mPrincipal, res.mIsWriteOnly,
                                             res.mCORSUsed);
     }
 
     if (res.mImageRequest) {
-      CanvasImageCache::NotifyDrawImage(imgElt, HTMLCanvasElement(),
+      CanvasImageCache::NotifyDrawImage(imgElt, mCanvasElement,
                                         res.mImageRequest, res.mSurface, imgSize);
     }
 
@@ -4009,8 +3990,7 @@ nsCanvasRenderingContext2DAzure::GetImageData(double aSx, double aSy,
 
   // Check only if we have a canvas element; if we were created with a docshell,
   // then it's special internal use.
-  if (mCanvasElement &&
-      HTMLCanvasElement()->IsWriteOnly() &&
+  if (mCanvasElement && mCanvasElement->IsWriteOnly() &&
       !nsContentUtils::IsCallerTrustedForRead())
   {
     // XXX ERRMSG we need to report an error to developers here! (bug 329026)
@@ -4407,7 +4387,7 @@ 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(HTMLCanvasElement());
+    userData = new CanvasRenderingContext2DUserData(mCanvasElement);
     canvasLayer->SetDidTransactionCallback(
             CanvasRenderingContext2DUserData::DidTransactionCallback, userData);
   }
diff --git a/content/html/content/public/nsHTMLCanvasElement.h b/content/html/content/public/nsHTMLCanvasElement.h
index 0c588f88b9c5..e020373b50dc 100644
--- a/content/html/content/public/nsHTMLCanvasElement.h
+++ b/content/html/content/public/nsHTMLCanvasElement.h
@@ -16,14 +16,14 @@
 #include "nsDOMError.h"
 #include "nsNodeInfoManager.h"
 
-#include "nsICanvasRenderingContextInternal.h"
 #include "nsICanvasElementExternal.h"
-#include "nsIDOMCanvasRenderingContext2D.h"
 #include "nsLayoutUtils.h"
 
 #include "Layers.h"
 
+class nsICanvasRenderingContextInternal;
 class nsIDOMFile;
+class nsIPropertyBag;
 
 class nsHTMLCanvasElement : public nsGenericHTMLElement,
                             public nsICanvasElementExternal,
diff --git a/content/html/content/src/nsHTMLCanvasElement.cpp b/content/html/content/src/nsHTMLCanvasElement.cpp
index 34c7c08ac4e0..169d3691c61a 100644
--- a/content/html/content/src/nsHTMLCanvasElement.cpp
+++ b/content/html/content/src/nsHTMLCanvasElement.cpp
@@ -11,6 +11,8 @@
 #include "prmem.h"
 #include "nsDOMFile.h"
 
+#include "nsICanvasRenderingContextInternal.h"
+#include "nsIDOMCanvasRenderingContext2D.h"
 #include "nsIScriptSecurityManager.h"
 #include "nsIXPConnect.h"
 #include "jsapi.h"
@@ -453,15 +455,9 @@ nsHTMLCanvasElement::GetContextHelper(const nsAString& aContextId,
     return NS_OK;
   }
 
-  rv = ctx->SetCanvasElement(this);
-  if (NS_FAILED(rv)) {
-    *aContext = nsnull;
-    return rv;
-  }
-
+  ctx->SetCanvasElement(this);
   ctx.forget(aContext);
-
-  return rv;
+  return NS_OK;
 }
 
 NS_IMETHODIMP