diff --git a/mozilla/gfx/idl/gfxIImageFrame.idl b/mozilla/gfx/idl/gfxIImageFrame.idl
index 7658a233216..9779af4627b 100644
--- a/mozilla/gfx/idl/gfxIImageFrame.idl
+++ b/mozilla/gfx/idl/gfxIImageFrame.idl
@@ -57,7 +57,7 @@ native nsRectRef(nsIntRect &);
  * @author Stuart Parmenter <pavlov@netscape.com>
  * @version 0.1
  */
-[scriptable, uuid(2502c898-73bd-4da5-8fae-21cf7a492f64)]
+[scriptable, uuid(7292afa2-3b94-424d-97d5-51ce2f04c0fe)]
 interface gfxIImageFrame : nsISupports
 {
   /**
@@ -156,4 +156,8 @@ interface gfxIImageFrame : nsISupports
    * moment
    */
   attribute long frameDisposalMethod;
+
+  /* PNG specific methods */
+
+  attribute long blendMethod;
 };
diff --git a/mozilla/gfx/src/shared/gfxImageFrame.cpp b/mozilla/gfx/src/shared/gfxImageFrame.cpp
index 060667c14d3..8ac40d9dc71 100644
--- a/mozilla/gfx/src/shared/gfxImageFrame.cpp
+++ b/mozilla/gfx/src/shared/gfxImageFrame.cpp
@@ -46,7 +46,8 @@ gfxImageFrame::gfxImageFrame() :
   mInitialized(PR_FALSE),
   mMutable(PR_TRUE),
   mTimeout(100),
-  mDisposalMethod(0)
+  mDisposalMethod(0), /* imgIContainer::kDisposeNotSpecified */
+  mBlendMethod(1) /* imgIContainer::kBlendOver */
 {
   /* member initializers and constructor code */
 }
@@ -343,6 +344,24 @@ NS_IMETHODIMP gfxImageFrame::SetFrameDisposalMethod(PRInt32 aFrameDisposalMethod
   return NS_OK;
 }
 
+/* attribute long blendMethod; */
+NS_IMETHODIMP gfxImageFrame::GetBlendMethod(PRInt32 *aBlendMethod)
+{
+  if (!mInitialized)
+    return NS_ERROR_NOT_INITIALIZED;
+
+  *aBlendMethod = mBlendMethod;
+  return NS_OK;
+}
+NS_IMETHODIMP gfxImageFrame::SetBlendMethod(PRInt32 aBlendMethod)
+{
+  if (!mInitialized)
+    return NS_ERROR_NOT_INITIALIZED;
+
+  mBlendMethod = (PRInt8)aBlendMethod;
+  return NS_OK;
+}
+
 NS_IMETHODIMP gfxImageFrame::GetInterface(const nsIID & aIID, void * *result)
 {
   if (!mInitialized)
diff --git a/mozilla/gfx/src/shared/gfxImageFrame.h b/mozilla/gfx/src/shared/gfxImageFrame.h
index d9f251461e5..80108af75af 100644
--- a/mozilla/gfx/src/shared/gfxImageFrame.h
+++ b/mozilla/gfx/src/shared/gfxImageFrame.h
@@ -80,4 +80,5 @@ private:
   PRInt32      mTimeout; // -1 means display forever
   nsIntPoint   mOffset;
   PRInt32      mDisposalMethod;
+  PRInt8       mBlendMethod;
 };
diff --git a/mozilla/modules/libpr0n/decoders/png/nsPNGDecoder.cpp b/mozilla/modules/libpr0n/decoders/png/nsPNGDecoder.cpp
index 83b74d378e2..0b00ef52d61 100644
--- a/mozilla/modules/libpr0n/decoders/png/nsPNGDecoder.cpp
+++ b/mozilla/modules/libpr0n/decoders/png/nsPNGDecoder.cpp
@@ -136,13 +136,13 @@ void nsPNGDecoder::SetAnimFrameInfo()
 {
   png_uint_16 delay_num, delay_den; /* in seconds */
   png_byte dispose_op;
+  png_byte blend_op;
   PRInt32 timeout; /* in milliseconds */
   
   delay_num = png_get_next_frame_delay_num(mPNG, mInfo);
   delay_den = png_get_next_frame_delay_den(mPNG, mInfo);
   dispose_op = png_get_next_frame_dispose_op(mPNG, mInfo);
-
-  // XXX need to handle blend_op here!
+  blend_op = png_get_next_frame_blend_op(mPNG, mInfo);
 
   if (delay_num == 0) {
     timeout = 0; // gfxImageFrame::SetTimeout() will set to a minimum
@@ -163,6 +163,11 @@ void nsPNGDecoder::SetAnimFrameInfo()
       mFrame->SetFrameDisposalMethod(imgIContainer::kDisposeClear);
   else
       mFrame->SetFrameDisposalMethod(imgIContainer::kDisposeKeep);
+  
+  if (blend_op == PNG_BLEND_OP_SOURCE)
+      mFrame->SetBlendMethod(imgIContainer::kBlendSource);
+  /*else // 'over' is the default for a gfxImageFrame
+      mFrame->SetBlendMethod(imgIContainer::kBlendOver); */
 }
 
 
diff --git a/mozilla/modules/libpr0n/public/imgIContainer.idl b/mozilla/modules/libpr0n/public/imgIContainer.idl
index 6897fb737ee..cc750212898 100644
--- a/mozilla/modules/libpr0n/public/imgIContainer.idl
+++ b/mozilla/modules/libpr0n/public/imgIContainer.idl
@@ -68,6 +68,16 @@ interface imgIContainer : nsISupports
   const long kDisposeClear            =  2; // Clear the frame's area, revealing bg
   const long kDisposeRestorePrevious  =  3; // Restore the previous (composited) frame
   
+  /*
+   * "Blend" method indicates how the current image is combined with the
+   * previous image.
+   */
+  const long kBlendSource             =  0; // All color components of the frame, including alpha, 
+                                            // overwrite the current contents of the frame's 
+                                            // output buffer region
+  const long kBlendOver               =  1; // The frame should be composited onto the output buffer 
+                                            // based on its alpha, using a simple OVER operation
+  
   /**
    * Create a new \a aWidth x \a aHeight sized image container.
    *
diff --git a/mozilla/modules/libpr0n/src/imgContainer.cpp b/mozilla/modules/libpr0n/src/imgContainer.cpp
index 616fc7de32f..ac1816b334e 100644
--- a/mozilla/modules/libpr0n/src/imgContainer.cpp
+++ b/mozilla/modules/libpr0n/src/imgContainer.cpp
@@ -943,7 +943,7 @@ nsresult imgContainer::DoComposite(gfxIImageFrame** aFrameToUse,
   }
 
   // Check if the frame we are composing wants the previous image restored afer
-  // it is done. Don't store it (again) if last frame wanted it's image restored
+  // it is done. Don't store it (again) if last frame wanted its image restored
   // too
   if ((nextFrameDisposalMethod == imgIContainer::kDisposeRestorePrevious) &&
       (prevFrameDisposalMethod != imgIContainer::kDisposeRestorePrevious)) {
@@ -1089,7 +1089,19 @@ nsresult imgContainer::DrawFrameTo(gfxIImageFrame *aSrc,
   dstImg->GetSurface(getter_AddRefs(dstSurf));
 
   gfxContext dst(dstSurf);
+  
+  // first clear the surface if the blend flag says so
+  PRInt32 blendMethod;
+  aSrc->GetBlendMethod(&blendMethod);
+  gfxContext::GraphicsOperator defaultOperator = dst.CurrentOperator();
+  if (blendMethod == imgIContainer::kBlendSource) {
+    dst.SetOperator(gfxContext::OPERATOR_CLEAR);
+    dst.Rectangle(gfxRect(aDstRect.x, aDstRect.y, aDstRect.width, aDstRect.height));
+    dst.Fill();
+  }
+  
   dst.NewPath();
+  dst.SetOperator(defaultOperator);
   // We don't use PixelSnappedRectangleAndSetPattern because if
   // these coords aren't already pixel aligned, we've lost
   // before we've even begun.