--- a/gfx/layers/d3d11/CompositorD3D11.cpp
+++ b/gfx/layers/d3d11/CompositorD3D11.cpp
@@ -27,16 +27,17 @@
 
 #include "mozilla/EnumeratedArray.h"
 #include "mozilla/Telemetry.h"
 #include "BlendShaderConstants.h"
 
 #include "D3D11ShareHandleImage.h"
 
 #include <VersionHelpers.h> // For IsWindows8OrGreater
+#include <winsdkver.h>
 
 namespace mozilla {
 
 using namespace gfx;
 
 namespace layers {
 
 static bool CanUsePartialPresents(ID3D11Device* aDevice);
@@ -486,21 +487,24 @@ CompositorD3D11::Initialize(nsCString* c
 
   {
     RefPtr<IDXGIFactory> dxgiFactory;
     dxgiAdapter->GetParent(IID_PPV_ARGS(dxgiFactory.StartAssignment()));
 
     RefPtr<IDXGIFactory2> dxgiFactory2;
     hr = dxgiFactory->QueryInterface((IDXGIFactory2**)getter_AddRefs(dxgiFactory2));
 
+#if (_WIN32_WINDOWS_MAXVER >= 0x0A00)
     if (gfxPrefs::Direct3D11UseDoubleBuffering() && SUCCEEDED(hr) && dxgiFactory2 && IsWindows10OrGreater()) {
       // DXGI_SCALING_NONE is not available on Windows 7 with Platform Update.
       // This looks awful for things like the awesome bar and browser window resizing
       // so we don't use a flip buffer chain here. When using EFFECT_SEQUENTIAL
       // it looks like windows doesn't stretch the surface when resizing.
+      // We chose not to run this on Windows 10 because it appears sometimes this breaks
+      // our ability to test ASAP compositing.
       RefPtr<IDXGISwapChain1> swapChain;
 
       DXGI_SWAP_CHAIN_DESC1 swapDesc;
       ::ZeroMemory(&swapDesc, sizeof(swapDesc));
       swapDesc.Width = 0;
       swapDesc.Height = 0;
       swapDesc.Format = DXGI_FORMAT_B8G8R8A8_UNORM;
       swapDesc.SampleDesc.Count = 1;
@@ -522,17 +526,19 @@ CompositorD3D11::Initialize(nsCString* c
         *out_failureReason = "FEATURE_FAILURE_D3D11_SWAP_CHAIN";
         return false;
       }
 
       DXGI_RGBA color = { 1.0f, 1.0f, 1.0f, 1.0f };
       swapChain->SetBackgroundColor(&color);
 
       mSwapChain = swapChain;
-    } else {
+    } else
+#endif
+    {
       DXGI_SWAP_CHAIN_DESC swapDesc;
       ::ZeroMemory(&swapDesc, sizeof(swapDesc));
       swapDesc.BufferDesc.Width = 0;
       swapDesc.BufferDesc.Height = 0;
       swapDesc.BufferDesc.Format = DXGI_FORMAT_B8G8R8A8_UNORM;
       swapDesc.BufferDesc.RefreshRate.Numerator = 60;
       swapDesc.BufferDesc.RefreshRate.Denominator = 1;
       swapDesc.SampleDesc.Count = 1;
@@ -818,16 +824,20 @@ CompositorD3D11::GetPSForEffect(Effect* 
     NS_WARNING("No shader to load");
     return nullptr;
   }
 }
 
 void
 CompositorD3D11::ClearRect(const gfx::Rect& aRect)
 {
+  if (aRect.IsEmpty()) {
+    return;
+  }
+
   mContext->OMSetBlendState(mAttachments->mDisabledBlendState, sBlendFactor, 0xFFFFFFFF);
 
   Matrix4x4 identity;
   memcpy(&mVSConstants.layerTransform, &identity._11, 64);
 
   mVSConstants.layerQuad = aRect;
   mVSConstants.renderTargetOffset[0] = 0;
   mVSConstants.renderTargetOffset[1] = 0;
@@ -849,18 +859,16 @@ CompositorD3D11::ClearRect(const gfx::Re
   mPSConstants.layerColor[3] = 0;
 
   if (!UpdateConstantBuffers()) {
     NS_WARNING("Failed to update shader constant buffers");
     return;
   }
 
   mContext->Draw(4, 0);
-
-  mContext->OMSetBlendState(mAttachments->mPremulBlendState, sBlendFactor, 0xFFFFFFFF);
 }
 
 static inline bool
 EffectHasPremultipliedAlpha(Effect* aEffect)
 {
   if (aEffect->mType == EffectTypes::RGB) {
     return static_cast<TexturedEffect*>(aEffect)->mPremultiplied;
   }
@@ -1353,18 +1361,22 @@ CompositorD3D11::BeginFrame(const nsIntR
   }
 
   mCurrentClip = mBackBufferInvalid.GetBounds();
 
   mContext->RSSetState(mAttachments->mRasterizerState);
 
   SetRenderTarget(mDefaultRT);
 
-  // ClearRect will set the correct blend state for us.
-  ClearRect(Rect(mCurrentClip.x, mCurrentClip.y, mCurrentClip.width, mCurrentClip.height));
+  IntRegion regionToClear(mCurrentClip);
+  regionToClear.Sub(regionToClear, aOpaqueRegion);
+
+  ClearRect(Rect(regionToClear.GetBounds()));
+
+  mContext->OMSetBlendState(mAttachments->mPremulBlendState, sBlendFactor, 0xFFFFFFFF);
 
   if (mAttachments->mSyncTexture) {
     RefPtr<IDXGIKeyedMutex> mutex;
     mAttachments->mSyncTexture->QueryInterface((IDXGIKeyedMutex**)getter_AddRefs(mutex));
 
     MOZ_ASSERT(mutex);
     {
       HRESULT hr;