diff --git a/gfx/layers/Layers.cpp b/gfx/layers/Layers.cpp
index 1d619180efd6..a1ffd9eb9366 100644
--- a/gfx/layers/Layers.cpp
+++ b/gfx/layers/Layers.cpp
@@ -200,6 +200,17 @@ LayerManager::CreateOptimalSurface(const gfxIntSize &aSize,
     CreateOffscreenSurface(aSize, gfxASurface::ContentFromFormat(aFormat));
 }
 
+#ifdef DEBUG
+void
+LayerManager::Mutated(Layer* aLayer)
+{
+  NS_ABORT_IF_FALSE(!aLayer->GetTileSourceRect() ||
+                    (LAYERS_BASIC == GetBackendType() &&
+                     Layer::TYPE_IMAGE == aLayer->GetType()),
+                    "Tiling not supported for this manager/layer type");
+}
+#endif  // DEBUG
+
 //--------------------------------------------------
 // Layer
 
diff --git a/gfx/layers/Layers.h b/gfx/layers/Layers.h
index 927c0c1bc75c..a31428b5779a 100644
--- a/gfx/layers/Layers.h
+++ b/gfx/layers/Layers.h
@@ -359,8 +359,15 @@ public:
   /**
    * CONSTRUCTION PHASE ONLY
    * Called when a managee has mutated.
+   * Subclasses overriding this method must first call their
+   * superclass's impl
    */
+#ifdef DEBUG
+  // In debug builds, we check some properties of |aLayer|.
+  virtual void Mutated(Layer* aLayer);
+#else
   virtual void Mutated(Layer* aLayer) { }
+#endif
 
   /**
    * CONSTRUCTION PHASE ONLY
@@ -641,6 +648,10 @@ public:
    * ColorLayers, a source rect for tiling doesn't make sense at all.
    *
    * If aRect is null no tiling will be performed. 
+   *
+   * NB: this interface is only implemented for BasicImageLayers, and
+   * then only for source rects the same size as the layers'
+   * underlying images.
    */
   void SetTileSourceRect(const nsIntRect* aRect)
   {
diff --git a/gfx/layers/basic/BasicLayers.cpp b/gfx/layers/basic/BasicLayers.cpp
index 57dba5534f62..2ca6bc62e992 100644
--- a/gfx/layers/basic/BasicLayers.cpp
+++ b/gfx/layers/basic/BasicLayers.cpp
@@ -667,7 +667,8 @@ public:
                      void* aCallbackData);
 
   static void PaintContext(gfxPattern* aPattern,
-                           const gfxIntSize& aSize,
+                           const nsIntRegion& aVisible,
+                           const nsIntRect* aTileSourceRect,
                            float aOpacity,
                            gfxContext* aContext);
 
@@ -712,13 +713,16 @@ BasicImageLayer::GetAndPaintCurrentImage(gfxContext* aContext,
 
   pat->SetFilter(mFilter);
 
-  PaintContext(pat, mSize, aOpacity, aContext); 
+  PaintContext(pat,
+               nsIntRegion(nsIntRect(0, 0, mSize.width, mSize.height)),
+               GetTileSourceRect(), aOpacity, aContext); 
   return pat.forget();
 }
 
 /*static*/ void
 BasicImageLayer::PaintContext(gfxPattern* aPattern,
-                              const gfxIntSize& aSize,
+                              const nsIntRegion& aVisible,
+                              const nsIntRect* aTileSourceRect,
                               float aOpacity,
                               gfxContext* aContext)
 {
@@ -736,14 +740,34 @@ BasicImageLayer::PaintContext(gfxPattern* aPattern,
     extend = gfxPattern::EXTEND_NONE;
   }
 
-  aPattern->SetExtend(extend);
+  if (!aTileSourceRect) {
+    aContext->NewPath();
+    // No need to snap here; our transform has already taken care of it.
+    // XXX true for arbitrary regions?  Don't care yet though
+    gfxUtils::PathFromRegion(aContext, aVisible);
+    aPattern->SetExtend(extend);
+    aContext->SetPattern(aPattern);
+    aContext->FillWithOpacity(aOpacity);
+  } else {
+    nsRefPtr<gfxASurface> source = aPattern->GetSurface();
+    NS_ABORT_IF_FALSE(source, "Expecting a surface pattern");
+    gfxIntSize sourceSize = source->GetSize();
+    nsIntRect sourceRect(0, 0, sourceSize.width, sourceSize.height);
+    NS_ABORT_IF_FALSE(sourceRect == *aTileSourceRect,
+                      "Cowardly refusing to create a temporary surface for tiling");
 
-  /* Draw RGB surface onto frame */
-  aContext->NewPath();
-  // No need to snap here; our transform has already taken care of it.
-  aContext->Rectangle(gfxRect(0, 0, aSize.width, aSize.height));
-  aContext->SetPattern(aPattern);
-  aContext->FillWithOpacity(aOpacity);
+    gfxContextAutoSaveRestore saveRestore(aContext);
+
+    aContext->NewPath();
+    gfxUtils::PathFromRegion(aContext, aVisible);
+
+    aPattern->SetExtend(gfxPattern::EXTEND_REPEAT);
+    aContext->SetPattern(aPattern);
+    aContext->FillWithOpacity(aOpacity);
+  }
+
+  // Reset extend mode for callers that need to reuse the pattern
+  aPattern->SetExtend(extend);
 }
 
 class BasicColorLayer : public ColorLayer, BasicImplData {
@@ -1890,7 +1914,9 @@ BasicShadowableImageLayer::Paint(gfxContext* aContext,
   }
 
   nsRefPtr<gfxContext> tmpCtx = new gfxContext(mBackSurface);
-  PaintContext(pat, mSize, 1.0, tmpCtx);
+  PaintContext(pat,
+               nsIntRegion(nsIntRect(0, 0, mSize.width, mSize.height)),
+               nsnull, 1.0, tmpCtx);
 
   BasicManager()->PaintedImage(BasicManager()->Hold(this),
                                mBackSurface);
@@ -2366,7 +2392,8 @@ BasicShadowImageLayer::Paint(gfxContext* aContext,
 
   nsRefPtr<gfxPattern> pat = new gfxPattern(mFrontSurface);
   pat->SetFilter(mFilter);
-  BasicImageLayer::PaintContext(pat, mSize, GetEffectiveOpacity(), aContext);
+  BasicImageLayer::PaintContext(
+    pat, GetEffectiveVisibleRegion(), GetTileSourceRect(), GetEffectiveOpacity(), aContext);
 }
 
 class BasicShadowColorLayer : public ShadowColorLayer,
@@ -2631,6 +2658,8 @@ BasicShadowLayerManager::SetRoot(Layer* aLayer)
 void
 BasicShadowLayerManager::Mutated(Layer* aLayer)
 {
+  BasicLayerManager::Mutated(aLayer);
+
   NS_ASSERTION(InConstruction() || InDrawing(), "wrong phase");
   if (HasShadowManager()) {
     ShadowLayerForwarder::Mutated(Hold(aLayer));
diff --git a/gfx/layers/ipc/PLayers.ipdl b/gfx/layers/ipc/PLayers.ipdl
index aa0732d8db3d..62b80fd146d1 100644
--- a/gfx/layers/ipc/PLayers.ipdl
+++ b/gfx/layers/ipc/PLayers.ipdl
@@ -122,6 +122,8 @@ struct CommonLayerAttributes {
   float opacity;
   bool useClipRect;
   nsIntRect clipRect;
+  bool useTileSourceRect;
+  nsIntRect tileSourceRect;
 };
 
 struct ThebesLayerAttributes {
diff --git a/gfx/layers/ipc/ShadowLayers.cpp b/gfx/layers/ipc/ShadowLayers.cpp
index eb63a3adfca0..6e051ed4cabc 100644
--- a/gfx/layers/ipc/ShadowLayers.cpp
+++ b/gfx/layers/ipc/ShadowLayers.cpp
@@ -345,6 +345,9 @@ ShadowLayerForwarder::EndTransaction(InfallibleTArray<EditReply>* aReplies)
     common.useClipRect() = !!mutant->GetClipRect();
     common.clipRect() = (common.useClipRect() ?
                          *mutant->GetClipRect() : nsIntRect());
+    common.useTileSourceRect() = !!mutant->GetTileSourceRect();
+    common.tileSourceRect() = (common.useTileSourceRect() ?
+                               *mutant->GetTileSourceRect() : nsIntRect());
     attrs.specific() = null_t();
     mutant->FillSpecificAttributes(attrs.specific());
 
diff --git a/gfx/layers/ipc/ShadowLayersParent.cpp b/gfx/layers/ipc/ShadowLayersParent.cpp
index 9c742047d183..b4c6f05e57ba 100644
--- a/gfx/layers/ipc/ShadowLayersParent.cpp
+++ b/gfx/layers/ipc/ShadowLayersParent.cpp
@@ -296,6 +296,7 @@ ShadowLayersParent::RecvUpdate(const InfallibleTArray<Edit>& cset,
       layer->SetOpacity(common.opacity());
       layer->SetClipRect(common.useClipRect() ? &common.clipRect() : NULL);
       layer->SetTransform(common.transform());
+      layer->SetTileSourceRect(common.useTileSourceRect() ? &common.tileSourceRect() : NULL);
 
       typedef SpecificLayerAttributes Specific;
       const SpecificLayerAttributes& specific = attrs.specific();