--- a/dom/canvas/CanvasRenderingContext2D.cpp
+++ b/dom/canvas/CanvasRenderingContext2D.cpp
@@ -4842,17 +4842,18 @@ CanvasRenderingContext2D::DrawWindow(nsG
     return;
   }
 
   RefPtr<gfxContext> thebes;
   RefPtr<DrawTarget> drawDT;
   // Rendering directly is faster and can be done if mTarget supports Azure
   // and does not need alpha blending.
   if (gfxPlatform::GetPlatform()->SupportsAzureContentForDrawTarget(mTarget) &&
-      GlobalAlpha() == 1.0f)
+      GlobalAlpha() == 1.0f &&
+      UsedOperation() == CompositionOp::OP_OVER)
   {
     thebes = new gfxContext(mTarget);
     thebes->SetMatrix(gfxMatrix(matrix._11, matrix._12, matrix._21,
                                 matrix._22, matrix._31, matrix._32));
   } else {
     drawDT =
       gfxPlatform::GetPlatform()->CreateOffscreenContentDrawTarget(IntSize(ceil(sw), ceil(sh)),
                                                                    SurfaceFormat::B8G8R8A8);
@@ -4887,17 +4888,17 @@ CanvasRenderingContext2D::DrawWindow(nsG
       error.Throw(NS_ERROR_FAILURE);
       return;
     }
 
     gfx::Rect destRect(0, 0, w, h);
     gfx::Rect sourceRect(0, 0, sw, sh);
     mTarget->DrawSurface(source, destRect, sourceRect,
                          DrawSurfaceOptions(gfx::Filter::POINT),
-                         DrawOptions(GlobalAlpha(), CompositionOp::OP_OVER,
+                         DrawOptions(GlobalAlpha(), UsedOperation(),
                                      AntialiasMode::NONE));
     mTarget->Flush();
   } else {
     mTarget->SetTransform(matrix);
   }
 
   // note that x and y are coordinates in the document that
   // we're drawing; x and y are drawn to 0,0 in current user

--- a/layout/base/nsPresShell.cpp
+++ b/layout/base/nsPresShell.cpp
@@ -4637,46 +4637,17 @@ PresShell::RenderDocument(const nsRect& 
     // Nothing to paint, just fill the rect
     aThebesContext->SetColor(Color::FromABGR(aBackgroundColor));
     aThebesContext->Fill();
     return NS_OK;
   }
 
   gfxContextAutoSaveRestore save(aThebesContext);
 
-  CompositionOp oldOp = aThebesContext->CurrentOp();
-  if (oldOp == CompositionOp::OP_OVER) {
-    // Clip to the destination rectangle before we push the group,
-    // to limit the size of the temporary surface
-    aThebesContext->Clip();
-  }
-
-  // we want the window to be composited as a single image using
-  // whatever operator was set; set OP_OVER here, which is
-  // either already the case, or overrides the operator in a group.
-  // the original operator will be present when we PopGroup.
-  // we can avoid using a temporary surface if we're using OP_OVER
-  bool needsGroup = oldOp != CompositionOp::OP_OVER;
-
-  if (needsGroup) {
-    aThebesContext->PushGroup(NS_GET_A(aBackgroundColor) == 0xff ?
-                              gfxContentType::COLOR :
-                              gfxContentType::COLOR_ALPHA);
-    aThebesContext->Save();
-
-    if (oldOp != CompositionOp::OP_OVER) {
-      // Clip now while we paint to the temporary surface. For
-      // non-source-bounded operators (e.g., SOURCE), we need to do clip
-      // here after we've pushed the group, so that eventually popping
-      // the group and painting it will be able to clear the entire
-      // destination surface.
-      aThebesContext->Clip();
-      aThebesContext->SetOp(CompositionOp::OP_OVER);
-    }
-  }
+  MOZ_ASSERT(aThebesContext->CurrentOp() == CompositionOp::OP_OVER);
 
   nsDeviceContext* devCtx = mPresContext->DeviceContext();
 
   gfxPoint offset(-nsPresContext::AppUnitsToFloatCSSPixels(aRect.x),
                   -nsPresContext::AppUnitsToFloatCSSPixels(aRect.y));
   gfxFloat scale = gfxFloat(devCtx->AppUnitsPerDevPixel())/nsPresContext::AppUnitsPerCSSPixel();
 
   // Since canvas APIs use floats to set up their matrices, we may have some
@@ -4738,23 +4709,16 @@ PresShell::RenderDocument(const nsRect& 
   // Don't let drawWindow blow away our retained layer tree
   if ((flags & nsLayoutUtils::PAINT_WIDGET_LAYERS) && wouldFlushRetainedLayers) {
     flags &= ~nsLayoutUtils::PAINT_WIDGET_LAYERS;
   }
 
   nsLayoutUtils::PaintFrame(&rc, rootFrame, nsRegion(aRect),
                             aBackgroundColor, flags);
 
-  // if we had to use a group, paint it to the destination now
-  if (needsGroup) {
-    aThebesContext->Restore();
-    aThebesContext->PopGroupToSource();
-    aThebesContext->Paint();
-  }
-
   return NS_OK;
 }
 
 /*
  * Clip the display list aList to a range. Returns the clipped
  * rectangle surrounding the range.
  */
 nsRect