diff --git a/gfx/layers/basic/BasicLayerManager.cpp b/gfx/layers/basic/BasicLayerManager.cpp
index 947638b41766..9eee33767087 100644
--- a/gfx/layers/basic/BasicLayerManager.cpp
+++ b/gfx/layers/basic/BasicLayerManager.cpp
@@ -1311,10 +1311,12 @@ BasicShadowLayerManager::ProgressiveUpdateCallback(bool aHasPendingNewThebesCont
     const gfx3DMatrix& rootTransform = GetRoot()->GetTransform();
     float devPixelRatioX = 1 / rootTransform.GetXScale();
     float devPixelRatioY = 1 / rootTransform.GetYScale();
-    gfx::Rect displayPort((metrics.mDisplayPort.x + metrics.mScrollOffset.x) * devPixelRatioX,
-                          (metrics.mDisplayPort.y + metrics.mScrollOffset.y) * devPixelRatioY,
-                          metrics.mDisplayPort.width * devPixelRatioX,
-                          metrics.mDisplayPort.height * devPixelRatioY);
+    const gfx::Rect& metricsDisplayPort = metrics.mCriticalDisplayPort.IsEmpty() ?
+      metrics.mDisplayPort : metrics.mCriticalDisplayPort;
+    gfx::Rect displayPort((metricsDisplayPort.x + metrics.mScrollOffset.x) * devPixelRatioX,
+                          (metricsDisplayPort.y + metrics.mScrollOffset.y) * devPixelRatioY,
+                          metricsDisplayPort.width * devPixelRatioX,
+                          metricsDisplayPort.height * devPixelRatioY);
 
     return AndroidBridge::Bridge()->ProgressiveUpdateCallback(
       aHasPendingNewThebesContent, displayPort, devPixelRatioX,
diff --git a/gfx/layers/basic/BasicTiledThebesLayer.cpp b/gfx/layers/basic/BasicTiledThebesLayer.cpp
index cacc1551bfea..94de90961c5d 100644
--- a/gfx/layers/basic/BasicTiledThebesLayer.cpp
+++ b/gfx/layers/basic/BasicTiledThebesLayer.cpp
@@ -388,6 +388,37 @@ BasicTiledThebesLayer::PaintThebes(gfxContext* aContext,
   if (invalidRegion.IsEmpty())
     return;
 
+  // Calculate the transform required to convert screen space into layer space
+  gfx3DMatrix transform = GetEffectiveTransform();
+  // XXX Not sure if this code for intermediate surfaces is correct.
+  //     It rarely gets hit though, and shouldn't have terrible consequences
+  //     even if it is wrong.
+  for (ContainerLayer* parent = GetParent(); parent; parent = parent->GetParent()) {
+    if (parent->UseIntermediateSurface()) {
+      transform.PreMultiply(parent->GetEffectiveTransform());
+    }
+  }
+  transform.Invert();
+
+  nsIntRect layerDisplayPort;
+  const gfx::Rect& criticalDisplayPort = GetParent()->GetFrameMetrics().mCriticalDisplayPort;
+  if (!criticalDisplayPort.IsEmpty()) {
+    // Find the critical display port in layer space.
+    gfxRect transformedCriticalDisplayPort = transform.TransformBounds(
+      gfxRect(criticalDisplayPort.x, criticalDisplayPort.y,
+              criticalDisplayPort.width, criticalDisplayPort.height));
+    transformedCriticalDisplayPort.RoundOut();
+    layerDisplayPort = nsIntRect(transformedCriticalDisplayPort.x,
+                                 transformedCriticalDisplayPort.y,
+                                 transformedCriticalDisplayPort.width,
+                                 transformedCriticalDisplayPort.height);
+
+    // Clip the invalid region to the critical display-port
+    invalidRegion.And(invalidRegion, layerDisplayPort);
+    if (invalidRegion.IsEmpty())
+      return;
+  }
+
   gfxSize resolution(1, 1);
   for (ContainerLayer* parent = GetParent(); parent; parent = parent->GetParent()) {
     const FrameMetrics& metrics = parent->GetFrameMetrics();
@@ -399,29 +430,23 @@ BasicTiledThebesLayer::PaintThebes(gfxContext* aContext,
   if (gfxPlatform::UseProgressiveTilePainting() &&
       !BasicManager()->HasShadowTarget() &&
       mTiledBuffer.GetResolution() == resolution) {
-    // Calculate the transform required to convert screen space into layer space
-    gfx3DMatrix transform = GetEffectiveTransform();
-    // XXX Not sure if this code for intermediate surfaces is correct.
-    //     It rarely gets hit though, and shouldn't have terrible consequences
-    //     even if it is wrong.
-    for (ContainerLayer* parent = GetParent(); parent; parent = parent->GetParent()) {
-      if (parent->UseIntermediateSurface()) {
-        transform.PreMultiply(parent->GetEffectiveTransform());
-      }
-    }
-    transform.Invert();
-
     // Store the old valid region, then clear it before painting.
     // We clip the old valid region to the visible region, as it only gets
     // used to decide stale content (currently valid and previously visible)
     nsIntRegion oldValidRegion = mTiledBuffer.GetValidRegion();
     oldValidRegion.And(oldValidRegion, mVisibleRegion);
+    if (!layerDisplayPort.IsEmpty()) {
+      oldValidRegion.And(oldValidRegion, layerDisplayPort);
+    }
     mTiledBuffer.ClearPaintedRegion();
 
     // Make sure that tiles that fall outside of the visible region are
     // discarded on the first update.
     if (!BasicManager()->IsRepeatTransaction()) {
       mValidRegion.And(mValidRegion, mVisibleRegion);
+      if (!layerDisplayPort.IsEmpty()) {
+        mValidRegion.And(mValidRegion, layerDisplayPort);
+      }
     }
 
     // Calculate the scroll offset since the last transaction.
@@ -472,6 +497,9 @@ BasicTiledThebesLayer::PaintThebes(gfxContext* aContext,
     mTiledBuffer.ClearPaintedRegion();
     mTiledBuffer.SetResolution(resolution);
     mValidRegion = mVisibleRegion;
+    if (!layerDisplayPort.IsEmpty()) {
+      mValidRegion.And(mValidRegion, layerDisplayPort);
+    }
     mTiledBuffer.PaintThebes(this, mValidRegion, invalidRegion, aCallback, aCallbackData);
   }
 
diff --git a/gfx/layers/ipc/CompositorParent.cpp b/gfx/layers/ipc/CompositorParent.cpp
index ab125205c740..5623c48cc3af 100644
--- a/gfx/layers/ipc/CompositorParent.cpp
+++ b/gfx/layers/ipc/CompositorParent.cpp
@@ -875,7 +875,8 @@ CompositorParent::TransformShadowTree(TimeStamp aCurrentFrame)
     // We synchronise the viewport information with Java after sending the above
     // notifications, so that Java can take these into account in its response.
     // Calculate the absolute display port to send to Java
-    gfx::Rect displayPortLayersPixels(metrics.mDisplayPort);
+    gfx::Rect displayPortLayersPixels(metrics.mCriticalDisplayPort.IsEmpty() ?
+                                      metrics.mDisplayPort : metrics.mCriticalDisplayPort);
     nsIntRect displayPortDevPixels(
       NS_lround(displayPortLayersPixels.x * devPixelRatioX),
       NS_lround(displayPortLayersPixels.y * devPixelRatioY),