diff --git a/dom/ipc/ContentParent.cpp b/dom/ipc/ContentParent.cpp
index 21a3a1cafe79..3eb9f64f6a8c 100644
--- a/dom/ipc/ContentParent.cpp
+++ b/dom/ipc/ContentParent.cpp
@@ -23,8 +23,6 @@
 
 #include "chrome/common/process_watcher.h"
 
-#include <set>
-
 #include "mozilla/a11y/PDocAccessible.h"
 #include "AppProcessChecker.h"
 #include "AudioChannelService.h"
@@ -90,6 +88,7 @@
 #include "mozilla/layers/PAPZParent.h"
 #include "mozilla/layers/CompositorThread.h"
 #include "mozilla/layers/ImageBridgeParent.h"
+#include "mozilla/layers/LayerTreeOwnerTracker.h"
 #include "mozilla/layers/SharedBufferManagerParent.h"
 #include "mozilla/layout/RenderFrameParent.h"
 #include "mozilla/LookAndFeel.h"
@@ -1685,18 +1684,6 @@ ContentParent::ProcessingError(Result aCode, const char* aReason)
   KillHard(aReason);
 }
 
-typedef std::pair<ContentParent*, std::set<uint64_t> > IDPair;
-
-namespace {
-std::map<ContentParent*, std::set<uint64_t> >&
-NestedBrowserLayerIds()
-{
-  MOZ_ASSERT(NS_IsMainThread());
-  static std::map<ContentParent*, std::set<uint64_t> > sNestedBrowserIds;
-  return sNestedBrowserIds;
-}
-} // namespace
-
 /* static */
 bool
 ContentParent::AllocateLayerTreeId(TabParent* aTabParent, uint64_t* aId)
@@ -1712,7 +1699,9 @@ ContentParent::AllocateLayerTreeId(ContentParent* aContent,
                                    uint64_t* aId)
 {
   GPUProcessManager* gpu = GPUProcessManager::Get();
+
   *aId = gpu->AllocateLayerTreeId();
+  gpu->MapLayerTreeId(*aId, aContent->OtherPid());
 
   if (!gfxPlatform::AsyncPanZoomEnabled()) {
     return true;
@@ -1748,33 +1737,22 @@ ContentParent::RecvAllocateLayerTreeId(const ContentParentId& aCpId,
     cpm->GetTopLevelTabParentByProcessAndTabId(aCpId, aTabId);
   MOZ_ASSERT(contentParent && browserParent);
 
-  if (!AllocateLayerTreeId(contentParent, browserParent, aTabId, aId)) {
-    return false;
-  }
-
-  auto iter = NestedBrowserLayerIds().find(this);
-  if (iter == NestedBrowserLayerIds().end()) {
-    std::set<uint64_t> ids;
-    ids.insert(*aId);
-    NestedBrowserLayerIds().insert(IDPair(this, ids));
-  } else {
-    iter->second.insert(*aId);
-  }
-  return true;
+  return AllocateLayerTreeId(contentParent, browserParent, aTabId, aId);
 }
 
 bool
 ContentParent::RecvDeallocateLayerTreeId(const uint64_t& aId)
 {
-  auto iter = NestedBrowserLayerIds().find(this);
-  if (iter != NestedBrowserLayerIds().end() &&
-      iter->second.find(aId) != iter->second.end())
+  GPUProcessManager* gpu = GPUProcessManager::Get();
+
+  if (!gpu->IsLayerTreeIdMapped(aId, this->OtherPid()))
   {
-    GPUProcessManager::Get()->DeallocateLayerTreeId(aId);
-  } else {
     // You can't deallocate layer tree ids that you didn't allocate
     KillHard("DeallocateLayerTreeId");
   }
+
+  gpu->DeallocateLayerTreeId(aId);
+
   return true;
 }
 
diff --git a/gfx/ipc/GPUParent.cpp b/gfx/ipc/GPUParent.cpp
index a9a58861eedc..6cf9b453aa9d 100644
--- a/gfx/ipc/GPUParent.cpp
+++ b/gfx/ipc/GPUParent.cpp
@@ -15,6 +15,7 @@
 #include "mozilla/layers/CompositorThread.h"
 #include "mozilla/layers/ImageBridgeParent.h"
 #include "nsDebugImpl.h"
+#include "mozilla/layers/LayerTreeOwnerTracker.h"
 #include "VRManager.h"
 #include "VRManagerParent.h"
 #include "VsyncBridgeParent.h"
@@ -62,6 +63,7 @@ GPUParent::Init(base::ProcessId aParentPid,
   }
   CompositorThreadHolder::Start();
   VRManager::ManagerInit();
+  LayerTreeOwnerTracker::Initialize();
   return true;
 }
 
@@ -222,6 +224,13 @@ GPUParent::RecvDeallocateLayerTreeId(const uint64_t& aLayersId)
   return true;
 }
 
+bool
+GPUParent::RecvAddLayerTreeIdMapping(const uint64_t& aLayersId, const ProcessId& aOwnerId)
+{
+  LayerTreeOwnerTracker::Get()->Map(aLayersId, aOwnerId);
+  return true;
+}
+
 void
 GPUParent::ActorDestroy(ActorDestroyReason aWhy)
 {
@@ -244,6 +253,7 @@ GPUParent::ActorDestroy(ActorDestroyReason aWhy)
   DeviceManagerDx::Shutdown();
   DeviceManagerD3D9::Shutdown();
 #endif
+  LayerTreeOwnerTracker::Shutdown();
   gfxVars::Shutdown();
   gfxConfig::Shutdown();
   gfxPrefs::DestroySingleton();
diff --git a/gfx/ipc/GPUParent.h b/gfx/ipc/GPUParent.h
index 28d977d690f6..6fefb731d660 100644
--- a/gfx/ipc/GPUParent.h
+++ b/gfx/ipc/GPUParent.h
@@ -43,6 +43,7 @@ public:
   bool RecvNewContentVRManager(Endpoint<PVRManagerParent>&& aEndpoint) override;
   bool RecvDeallocateLayerTreeId(const uint64_t& aLayersId) override;
   bool RecvGetDeviceStatus(GPUDeviceData* aOutStatus) override;
+  bool RecvAddLayerTreeIdMapping(const uint64_t& aLayersId, const ProcessId& aOwnerId) override;
 
   void ActorDestroy(ActorDestroyReason aWhy) override;
 
diff --git a/gfx/ipc/GPUProcessManager.cpp b/gfx/ipc/GPUProcessManager.cpp
index df5839cf2224..6c145ee81d85 100644
--- a/gfx/ipc/GPUProcessManager.cpp
+++ b/gfx/ipc/GPUProcessManager.cpp
@@ -6,10 +6,13 @@
 #include "GPUProcessManager.h"
 #include "GPUProcessHost.h"
 #include "mozilla/StaticPtr.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/layers/APZCTreeManager.h"
 #include "mozilla/layers/CompositorBridgeParent.h"
 #include "mozilla/layers/ImageBridgeChild.h"
 #include "mozilla/layers/ImageBridgeParent.h"
 #include "mozilla/layers/InProcessCompositorSession.h"
+#include "mozilla/layers/LayerTreeOwnerTracker.h"
 #include "mozilla/layers/RemoteCompositorSession.h"
 #include "mozilla/widget/PlatformWidgetTypes.h"
 #ifdef MOZ_WIDGET_SUPPORTS_OOP_COMPOSITING
@@ -57,10 +60,14 @@ GPUProcessManager::GPUProcessManager()
 {
   mObserver = new Observer(this);
   nsContentUtils::RegisterShutdownObserver(mObserver);
+
+  LayerTreeOwnerTracker::Initialize();
 }
 
 GPUProcessManager::~GPUProcessManager()
 {
+  LayerTreeOwnerTracker::Shutdown();
+
   // The GPU process should have already been shut down.
   MOZ_ASSERT(!mProcess && !mGPUChild);
 
@@ -505,6 +512,24 @@ GPUProcessManager::GetAPZCTreeManagerForLayers(uint64_t aLayersId)
   return CompositorBridgeParent::GetAPZCTreeManager(aLayersId);
 }
 
+void
+GPUProcessManager::MapLayerTreeId(uint64_t aLayersId, base::ProcessId aOwningId)
+{
+  LayerTreeOwnerTracker::Get()->Map(aLayersId, aOwningId);
+
+  if (mGPUChild) {
+    mGPUChild->SendAddLayerTreeIdMapping(
+        aLayersId,
+        aOwningId);
+  }
+}
+
+bool
+GPUProcessManager::IsLayerTreeIdMapped(uint64_t aLayersId, base::ProcessId aRequestingId)
+{
+  return LayerTreeOwnerTracker::Get()->IsMapped(aLayersId, aRequestingId);
+}
+
 uint64_t
 GPUProcessManager::AllocateLayerTreeId()
 {
diff --git a/gfx/ipc/GPUProcessManager.h b/gfx/ipc/GPUProcessManager.h
index 33e9868e9ec2..1ca8e8efa3ef 100644
--- a/gfx/ipc/GPUProcessManager.h
+++ b/gfx/ipc/GPUProcessManager.h
@@ -93,6 +93,13 @@ public:
   // pan/zoom-related events can be sent.
   already_AddRefed<IAPZCTreeManager> GetAPZCTreeManagerForLayers(uint64_t aLayersId);
 
+  // Maps the layer tree and process together so that aOwningPID is allowed
+  // to access aLayersId across process.
+  void MapLayerTreeId(uint64_t aLayersId, base::ProcessId aOwningId);
+
+  // Checks to see if aLayersId and aRequestingPID have been mapped by MapLayerTreeId
+  bool IsLayerTreeIdMapped(uint64_t aLayersId, base::ProcessId aRequestingId);
+
   // Allocate an ID that can be used to refer to a layer tree and
   // associated resources that live only on the compositor thread.
   //
diff --git a/gfx/ipc/PGPU.ipdl b/gfx/ipc/PGPU.ipdl
index 69b862216295..21e6daf9a827 100644
--- a/gfx/ipc/PGPU.ipdl
+++ b/gfx/ipc/PGPU.ipdl
@@ -9,6 +9,7 @@ include protocol PImageBridge;
 include protocol PVRManager;
 include protocol PVsyncBridge;
 
+using base::ProcessId from "base/process.h";
 using mozilla::TimeDuration from "mozilla/TimeStamp.h";
 using mozilla::CSSToLayoutDeviceScale from "Units.h";
 using mozilla::gfx::IntSize from "mozilla/gfx/2D.h";
@@ -58,6 +59,9 @@ parent:
 
   async DeallocateLayerTreeId(uint64_t layersId);
 
+  // Called to notify the GPU process of who owns a layersId.
+  sync AddLayerTreeIdMapping(uint64_t layersId, ProcessId ownerId);
+
   // Request the current DeviceStatus from the GPU process. This blocks until
   // one is available (i.e., Init has completed).
   sync GetDeviceStatus() returns (GPUDeviceData status);
diff --git a/gfx/layers/apz/util/ScrollLinkedEffectDetector.cpp b/gfx/layers/apz/util/ScrollLinkedEffectDetector.cpp
index 56b593f300da..758b705a3615 100644
--- a/gfx/layers/apz/util/ScrollLinkedEffectDetector.cpp
+++ b/gfx/layers/apz/util/ScrollLinkedEffectDetector.cpp
@@ -6,6 +6,7 @@
 #include "ScrollLinkedEffectDetector.h"
 
 #include "nsIDocument.h"
+#include "nsThreadUtils.h"
 
 namespace mozilla {
 namespace layers {
diff --git a/gfx/layers/ipc/APZCTreeManagerParent.cpp b/gfx/layers/ipc/APZCTreeManagerParent.cpp
index c9af1ba0cdec..9c7b9a8fd1e5 100644
--- a/gfx/layers/ipc/APZCTreeManagerParent.cpp
+++ b/gfx/layers/ipc/APZCTreeManagerParent.cpp
@@ -12,8 +12,9 @@
 namespace mozilla {
 namespace layers {
 
-APZCTreeManagerParent::APZCTreeManagerParent(RefPtr<APZCTreeManager> aAPZCTreeManager)
-  : mTreeManager(aAPZCTreeManager)
+APZCTreeManagerParent::APZCTreeManagerParent(uint64_t aLayersId, RefPtr<APZCTreeManager> aAPZCTreeManager)
+  : mLayersId(aLayersId)
+  , mTreeManager(aAPZCTreeManager)
 {
   MOZ_ASSERT(aAPZCTreeManager != nullptr);
 }
@@ -138,6 +139,12 @@ APZCTreeManagerParent::RecvZoomToRect(
     const CSSRect& aRect,
     const uint32_t& aFlags)
 {
+  if (aGuid.mLayersId != mLayersId) {
+    // Guard against bad data from hijacked child processes
+    NS_ERROR("Unexpected layers id in RecvZoomToRect; dropping message...");
+    return false;
+  }
+
   mTreeManager->ZoomToRect(aGuid, aRect, aFlags);
   return true;
 }
@@ -156,6 +163,14 @@ APZCTreeManagerParent::RecvSetTargetAPZC(
     const uint64_t& aInputBlockId,
     nsTArray<ScrollableLayerGuid>&& aTargets)
 {
+  for (size_t i = 0; i < aTargets.Length(); i++) {
+    if (aTargets[i].mLayersId != mLayersId) {
+      // Guard against bad data from hijacked child processes
+      NS_ERROR("Unexpected layers id in RecvSetTargetAPZC; dropping message...");
+      return false;
+    }
+  }
+
   mTreeManager->SetTargetAPZC(aInputBlockId, aTargets);
   return true;
 }
@@ -165,6 +180,12 @@ APZCTreeManagerParent::RecvUpdateZoomConstraints(
     const ScrollableLayerGuid& aGuid,
     const MaybeZoomConstraints& aConstraints)
 {
+  if (aGuid.mLayersId != mLayersId) {
+    // Guard against bad data from hijacked child processes
+    NS_ERROR("Unexpected layers id in RecvUpdateZoomConstraints; dropping message...");
+    return false;
+  }
+
   mTreeManager->UpdateZoomConstraints(aGuid, aConstraints);
   return true;
 }
@@ -172,6 +193,12 @@ APZCTreeManagerParent::RecvUpdateZoomConstraints(
 bool
 APZCTreeManagerParent::RecvCancelAnimation(const ScrollableLayerGuid& aGuid)
 {
+  if (aGuid.mLayersId != mLayersId) {
+    // Guard against bad data from hijacked child processes
+    NS_ERROR("Unexpected layers id in RecvCancelAnimation; dropping message...");
+    return false;
+  }
+
   mTreeManager->CancelAnimation(aGuid);
   return true;
 }
@@ -204,6 +231,12 @@ APZCTreeManagerParent::RecvStartScrollbarDrag(
     const ScrollableLayerGuid& aGuid,
     const AsyncDragMetrics& aDragMetrics)
 {
+  if (aGuid.mLayersId != mLayersId) {
+    // Guard against bad data from hijacked child processes
+    NS_ERROR("Unexpected layers id in RecvStartScrollbarDrag; dropping message...");
+    return false;
+  }
+
   mTreeManager->StartScrollbarDrag(aGuid, aDragMetrics);
   return true;
 }
diff --git a/gfx/layers/ipc/APZCTreeManagerParent.h b/gfx/layers/ipc/APZCTreeManagerParent.h
index a46cc50dc4da..855d462ea40f 100644
--- a/gfx/layers/ipc/APZCTreeManagerParent.h
+++ b/gfx/layers/ipc/APZCTreeManagerParent.h
@@ -19,7 +19,7 @@ class APZCTreeManagerParent
 {
 public:
 
-  explicit APZCTreeManagerParent(RefPtr<APZCTreeManager> aAPZCTreeManager);
+  explicit APZCTreeManagerParent(uint64_t aLayersId, RefPtr<APZCTreeManager> aAPZCTreeManager);
   virtual ~APZCTreeManagerParent() { }
 
   bool
@@ -133,6 +133,7 @@ public:
   ActorDestroy(ActorDestroyReason aWhy) override { }
 
 private:
+  uint64_t mLayersId;
   RefPtr<APZCTreeManager> mTreeManager;
 };
 
diff --git a/gfx/layers/ipc/CompositorBridgeChild.cpp b/gfx/layers/ipc/CompositorBridgeChild.cpp
index 94c3fa24c668..5ec651d141d8 100644
--- a/gfx/layers/ipc/CompositorBridgeChild.cpp
+++ b/gfx/layers/ipc/CompositorBridgeChild.cpp
@@ -13,6 +13,8 @@
 #include "base/task.h"                  // for NewRunnableMethod, etc
 #include "gfxPrefs.h"
 #include "mozilla/layers/ImageBridgeChild.h"
+#include "mozilla/layers/IAPZCTreeManager.h"
+#include "mozilla/layers/APZCTreeManagerChild.h"
 #include "mozilla/layers/LayerTransactionChild.h"
 #include "mozilla/layers/PLayerTransactionChild.h"
 #include "mozilla/layers/TextureClient.h"// for TextureClient
@@ -1007,6 +1009,41 @@ CompositorBridgeChild::DeallocPCompositorWidgetChild(PCompositorWidgetChild* aAc
 #endif
 }
 
+RefPtr<IAPZCTreeManager>
+CompositorBridgeChild::GetAPZCTreeManager(uint64_t aLayerTreeId)
+{
+  bool apzEnabled = false;
+  Unused << SendAsyncPanZoomEnabled(aLayerTreeId, &apzEnabled);
+
+  if (!apzEnabled) {
+    return nullptr;
+  }
+
+  PAPZCTreeManagerChild* child = SendPAPZCTreeManagerConstructor(aLayerTreeId);
+  if (!child) {
+    return nullptr;
+  }
+  APZCTreeManagerChild* parent = static_cast<APZCTreeManagerChild*>(child);
+
+  return RefPtr<IAPZCTreeManager>(parent);
+}
+
+PAPZCTreeManagerChild*
+CompositorBridgeChild::AllocPAPZCTreeManagerChild(const uint64_t& aLayersId)
+{
+  APZCTreeManagerChild* child = new APZCTreeManagerChild();
+  child->AddRef();
+  return child;
+}
+
+bool
+CompositorBridgeChild::DeallocPAPZCTreeManagerChild(PAPZCTreeManagerChild* aActor)
+{
+  APZCTreeManagerChild* parent = static_cast<APZCTreeManagerChild*>(aActor);
+  parent->Release();
+  return true;
+}
+
 void
 CompositorBridgeChild::ProcessingError(Result aCode, const char* aReason)
 {
diff --git a/gfx/layers/ipc/CompositorBridgeChild.h b/gfx/layers/ipc/CompositorBridgeChild.h
index 97c070283bb4..5a91dc095674 100644
--- a/gfx/layers/ipc/CompositorBridgeChild.h
+++ b/gfx/layers/ipc/CompositorBridgeChild.h
@@ -34,6 +34,8 @@ namespace layers {
 
 using mozilla::dom::TabChild;
 
+class IAPZCTreeManager;
+class APZCTreeManagerChild;
 class ClientLayerManager;
 class CompositorBridgeParent;
 class TextureClient;
@@ -209,6 +211,11 @@ public:
   PCompositorWidgetChild* AllocPCompositorWidgetChild(const CompositorWidgetInitData& aInitData) override;
   bool DeallocPCompositorWidgetChild(PCompositorWidgetChild* aActor) override;
 
+  RefPtr<IAPZCTreeManager> GetAPZCTreeManager(uint64_t aLayerTreeId);
+
+  PAPZCTreeManagerChild* AllocPAPZCTreeManagerChild(const uint64_t& aLayersId) override;
+  bool DeallocPAPZCTreeManagerChild(PAPZCTreeManagerChild* aActor) override;
+
   virtual ShmemAllocator* AsShmemAllocator() override { return this; }
 
   void ProcessingError(Result aCode, const char* aReason) override;
diff --git a/gfx/layers/ipc/CompositorBridgeParent.cpp b/gfx/layers/ipc/CompositorBridgeParent.cpp
index aa38525f1a17..b274800e11d4 100644
--- a/gfx/layers/ipc/CompositorBridgeParent.cpp
+++ b/gfx/layers/ipc/CompositorBridgeParent.cpp
@@ -32,6 +32,7 @@
 #include "VRManager.h"                  // for VRManager
 #include "mozilla/ipc/Transport.h"      // for Transport
 #include "mozilla/layers/APZCTreeManager.h"  // for APZCTreeManager
+#include "mozilla/layers/APZCTreeManagerParent.h"  // for APZCTreeManagerParent
 #include "mozilla/layers/APZThreadUtils.h"  // for APZCTreeManager
 #include "mozilla/layers/AsyncCompositionManager.h"
 #include "mozilla/layers/BasicCompositor.h"  // for BasicCompositor
@@ -42,6 +43,7 @@
 #include "mozilla/layers/FrameUniformityData.h"
 #include "mozilla/layers/ImageBridgeParent.h"
 #include "mozilla/layers/LayerManagerComposite.h"
+#include "mozilla/layers/LayerTreeOwnerTracker.h"
 #include "mozilla/layers/LayersTypes.h"
 #include "mozilla/layers/PLayerTransactionParent.h"
 #include "mozilla/layers/RemoteContentController.h"
@@ -1350,6 +1352,30 @@ CompositorBridgeParent::ForceComposeToTarget(DrawTarget* aTarget, const gfx::Int
   mCompositorScheduler->ForceComposeToTarget(aTarget, aRect);
 }
 
+PAPZCTreeManagerParent*
+CompositorBridgeParent::AllocPAPZCTreeManagerParent(const uint64_t& aLayersId)
+{
+  return nullptr;
+}
+
+bool
+CompositorBridgeParent::DeallocPAPZCTreeManagerParent(PAPZCTreeManagerParent* aActor)
+{
+  return false;
+}
+
+bool
+CompositorBridgeParent::RecvAsyncPanZoomEnabled(const uint64_t& aLayersId, bool* aHasAPZ)
+{
+  return false;
+}
+
+RefPtr<APZCTreeManager>
+CompositorBridgeParent::GetAPZCTreeManager()
+{
+  return mApzcTreeManager;
+}
+
 bool
 CompositorBridgeParent::CanComposite()
 {
@@ -2169,6 +2195,11 @@ public:
     return false;
   }
 
+  virtual bool RecvAsyncPanZoomEnabled(const uint64_t& aLayersId, bool* aHasAPZ) override;
+
+  virtual PAPZCTreeManagerParent* AllocPAPZCTreeManagerParent(const uint64_t& aLayersId) override;
+  virtual bool DeallocPAPZCTreeManagerParent(PAPZCTreeManagerParent* aActor) override;
+
   virtual CompositorBridgeParentIPCAllocator* AsCompositorBridgeParentIPCAllocator() override { return this; }
 
   virtual void UpdatePaintTime(LayerTransactionParent* aLayerTree, const TimeDuration& aPaintTime) override {
@@ -2459,6 +2490,12 @@ CrossProcessCompositorBridgeParent::AllocPLayerTransactionParent(
 {
   MOZ_ASSERT(aId != 0);
 
+  // Check to see if this child process has access to this layer tree.
+  if (!LayerTreeOwnerTracker::Get()->IsMapped(aId, OtherPid())) {
+    NS_ERROR("Unexpected layers id in AllocPLayerTransactionParent; dropping message...");
+    return nullptr;
+  }
+
   MonitorAutoLock lock(*sIndirectLayerTreesLock);
 
   CompositorBridgeParent::LayerTreeState* state = nullptr;
@@ -2497,6 +2534,44 @@ CrossProcessCompositorBridgeParent::DeallocPLayerTransactionParent(PLayerTransac
   return true;
 }
 
+bool
+CrossProcessCompositorBridgeParent::RecvAsyncPanZoomEnabled(const uint64_t& aLayersId, bool* aHasAPZ)
+{
+  // Check to see if this child process has access to this layer tree.
+  if (!LayerTreeOwnerTracker::Get()->IsMapped(aLayersId, OtherPid())) {
+    NS_ERROR("Unexpected layers id in RecvAsyncPanZoomEnabled; dropping message...");
+    return false;
+  }
+
+  MonitorAutoLock lock(*sIndirectLayerTreesLock);
+  CompositorBridgeParent::LayerTreeState& state = sIndirectLayerTrees[aLayersId];
+
+  *aHasAPZ = state.mParent ? state.mParent->AsyncPanZoomEnabled() : false;
+  return true;
+}
+
+PAPZCTreeManagerParent*
+CrossProcessCompositorBridgeParent::AllocPAPZCTreeManagerParent(const uint64_t& aLayersId)
+{
+  // Check to see if this child process has access to this layer tree.
+  if (!LayerTreeOwnerTracker::Get()->IsMapped(aLayersId, OtherPid())) {
+    NS_ERROR("Unexpected layers id in AllocPAPZCTreeManagerParent; dropping message...");
+    return nullptr;
+  }
+
+  MonitorAutoLock lock(*sIndirectLayerTreesLock);
+  CompositorBridgeParent::LayerTreeState& state = sIndirectLayerTrees[aLayersId];
+
+  MOZ_ASSERT(state.mParent);
+  return new APZCTreeManagerParent(aLayersId, state.mParent->GetAPZCTreeManager());
+}
+bool
+CrossProcessCompositorBridgeParent::DeallocPAPZCTreeManagerParent(PAPZCTreeManagerParent* aActor)
+{
+  delete aActor;
+  return true;
+}
+
 bool
 CrossProcessCompositorBridgeParent::RecvNotifyChildCreated(const uint64_t& child)
 {
diff --git a/gfx/layers/ipc/CompositorBridgeParent.h b/gfx/layers/ipc/CompositorBridgeParent.h
index 734b8f25f933..d1a941ef5ef3 100644
--- a/gfx/layers/ipc/CompositorBridgeParent.h
+++ b/gfx/layers/ipc/CompositorBridgeParent.h
@@ -489,6 +489,13 @@ public:
 
   void ForceComposeToTarget(gfx::DrawTarget* aTarget, const gfx::IntRect* aRect = nullptr);
 
+  PAPZCTreeManagerParent* AllocPAPZCTreeManagerParent(const uint64_t& aLayersId) override;
+  bool DeallocPAPZCTreeManagerParent(PAPZCTreeManagerParent* aActor) override;
+
+  bool RecvAsyncPanZoomEnabled(const uint64_t& aLayersId, bool* aHasAPZ) override;
+
+  RefPtr<APZCTreeManager> GetAPZCTreeManager();
+
   bool AsyncPanZoomEnabled() const {
     return !!mApzcTreeManager;
   }
diff --git a/gfx/layers/ipc/LayerTreeOwnerTracker.cpp b/gfx/layers/ipc/LayerTreeOwnerTracker.cpp
new file mode 100644
index 000000000000..7fc08c3edea0
--- /dev/null
+++ b/gfx/layers/ipc/LayerTreeOwnerTracker.cpp
@@ -0,0 +1,64 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=99: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "LayerTreeOwnerTracker.h"
+
+#include "mozilla/StaticPtr.h"              // for StaticAutoPtr
+#include "mozilla/dom/ContentParent.h"      // for ContentParent
+#include "mozilla/gfx/GPUChild.h"           // for GPUChild
+#include "mozilla/gfx/GPUProcessManager.h"  // for GPUProcessManager
+
+#include <utility> // for std::make_pair
+
+namespace mozilla {
+namespace layers {
+
+static StaticAutoPtr<LayerTreeOwnerTracker> sSingleton;
+
+LayerTreeOwnerTracker::LayerTreeOwnerTracker() :
+  mLayerIdsLock("LayerTreeOwnerTrackerLock")
+{
+}
+
+void
+LayerTreeOwnerTracker::Initialize()
+{
+  MOZ_ASSERT(!sSingleton);
+  sSingleton = new LayerTreeOwnerTracker();
+}
+
+void
+LayerTreeOwnerTracker::Shutdown()
+{
+  sSingleton = nullptr;
+}
+
+LayerTreeOwnerTracker*
+LayerTreeOwnerTracker::Get()
+{
+  return sSingleton;
+}
+
+void
+LayerTreeOwnerTracker::Map(uint64_t aLayersId, base::ProcessId aProcessId)
+{
+  MutexAutoLock lock(mLayerIdsLock);
+
+  // Add the mapping to the list
+  mLayerIds[aLayersId] = aProcessId;
+}
+
+bool
+LayerTreeOwnerTracker::IsMapped(uint64_t aLayersId, base::ProcessId aProcessId)
+{
+  MutexAutoLock lock(mLayerIdsLock);
+
+  auto iter = mLayerIds.find(aLayersId);
+  return iter != mLayerIds.end() && iter->second == aProcessId;
+}
+
+} // namespace layers
+} // namespace mozilla
diff --git a/gfx/layers/ipc/LayerTreeOwnerTracker.h b/gfx/layers/ipc/LayerTreeOwnerTracker.h
new file mode 100644
index 000000000000..67809e4e5c66
--- /dev/null
+++ b/gfx/layers/ipc/LayerTreeOwnerTracker.h
@@ -0,0 +1,62 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set sw=4 ts=8 et tw=80 : */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_layers_LayerTreeOwnerTracker_h
+#define mozilla_layers_LayerTreeOwnerTracker_h
+
+#include "base/process.h"  // for base::ProcessId
+#include "mozilla/Mutex.h" // for mozilla::Mutex
+
+#include <map>
+
+namespace mozilla {
+
+namespace dom {
+  class ContentParent;
+}
+
+namespace layers {
+
+/**
+ * A utility class for tracking which content processes should be allowed
+ * to access which layer trees.
+ *
+ * ProcessId's are used to track which content process can access the layer
+ * tree, and in the case of nested browser's we use the top level content
+ * processes' ProcessId.
+ *
+ * This class is only available in the main process and gpu process. Mappings
+ * are synced from main process to the gpu process. The actual syncing happens
+ * in GPUProcessManager, and so this class should not be used directly.
+ */
+class LayerTreeOwnerTracker final
+{
+public:
+  static void Initialize();
+  static void Shutdown();
+  static LayerTreeOwnerTracker* Get();
+
+  /**
+   * Map aLayersId and aProcessId together so that that process
+   * can access that layer tree.
+   */
+  void Map(uint64_t aLayersId, base::ProcessId aProcessId);
+  /**
+   * Checks whether it is okay for aProcessId to access aLayersId.
+   */
+  bool IsMapped(uint64_t aLayersId, base::ProcessId aProcessId);
+
+private:
+  LayerTreeOwnerTracker();
+
+  mozilla::Mutex mLayerIdsLock;
+  std::map<uint64_t, base::ProcessId> mLayerIds;
+};
+
+} // namespace layers
+} // namespace mozilla
+
+#endif // mozilla_layers_LayerTreeOwnerTracker_h
diff --git a/gfx/layers/ipc/PAPZCTreeManager.ipdl b/gfx/layers/ipc/PAPZCTreeManager.ipdl
index 134460317b69..ee3b8cae57f1 100644
--- a/gfx/layers/ipc/PAPZCTreeManager.ipdl
+++ b/gfx/layers/ipc/PAPZCTreeManager.ipdl
@@ -6,6 +6,8 @@
 include "mozilla/GfxMessageUtils.h";
 include "ipc/nsGUIEventIPC.h";
 
+include protocol PCompositorBridge;
+
 using CSSRect from "Units.h";
 using LayoutDeviceIntPoint from "Units.h";
 using ScreenPoint from "Units.h";
@@ -34,6 +36,8 @@ namespace layers {
 
 sync protocol PAPZCTreeManager
 {
+manager PCompositorBridge;
+
 parent:
 
   sync ReceiveMultiTouchInputEvent(MultiTouchInput aEvent)
diff --git a/gfx/layers/ipc/PCompositorBridge.ipdl b/gfx/layers/ipc/PCompositorBridge.ipdl
index 584d927034e7..6e02f3274a2d 100644
--- a/gfx/layers/ipc/PCompositorBridge.ipdl
+++ b/gfx/layers/ipc/PCompositorBridge.ipdl
@@ -8,6 +8,7 @@
 include LayersSurfaces;
 include LayersMessages;
 include PlatformWidgetTypes;
+include protocol PAPZCTreeManager;
 include protocol PBrowser;
 include protocol PCompositable;
 include protocol PCompositorWidget;
@@ -46,6 +47,7 @@ namespace layers {
  */
 sync protocol PCompositorBridge
 {
+  manages PAPZCTreeManager;
   // A Compositor manages a single Layer Manager (PLayerTransaction)
   manages PLayerTransaction;
   manages PTexture;
@@ -119,6 +121,12 @@ parent:
   // When out-of-process, this must be called to finish initialization.
   sync Initialize(uint64_t rootLayerTreeId);
 
+  // Returns whether this Compositor has APZ enabled or not.
+  sync AsyncPanZoomEnabled(uint64_t layersId) returns (bool aHasAPZ);
+
+  // Must be called after Initialize(), and only succeeds if AsyncPanZoomEnabled() is true.
+  async PAPZCTreeManager(uint64_t layersId);
+
   /**
    * Confirmation callback for UpdatePluginConfigurations and HideAllPlugins.
    */
diff --git a/gfx/layers/moz.build b/gfx/layers/moz.build
index 9347d27cb22b..732449437002 100644
--- a/gfx/layers/moz.build
+++ b/gfx/layers/moz.build
@@ -173,6 +173,7 @@ EXPORTS.mozilla.layers += [
     'ipc/LayerAnimationUtils.h',
     'ipc/LayerTransactionChild.h',
     'ipc/LayerTransactionParent.h',
+    'ipc/LayerTreeOwnerTracker.h',
     'ipc/RemoteContentController.h',
     'ipc/ShadowLayerChild.h',
     'ipc/ShadowLayers.h',
@@ -363,6 +364,7 @@ UNIFIED_SOURCES += [
     'ipc/LayerAnimationUtils.cpp',
     'ipc/LayerTransactionChild.cpp',
     'ipc/LayerTransactionParent.cpp',
+    'ipc/LayerTreeOwnerTracker.cpp',
     'ipc/RemoteContentController.cpp',
     'ipc/ShadowLayerChild.cpp',
     'ipc/ShadowLayerParent.cpp',