diff --git a/gfx/layers/ipc/CompositorParent.cpp b/gfx/layers/ipc/CompositorParent.cpp
index b1b4b4c30bb5..5877d1b76f52 100644
--- a/gfx/layers/ipc/CompositorParent.cpp
+++ b/gfx/layers/ipc/CompositorParent.cpp
@@ -1015,6 +1015,9 @@ EraseLayerState(uint64_t aId)
 CompositorParent::DeallocateLayerTreeId(uint64_t aId)
 {
   MOZ_ASSERT(NS_IsMainThread());
+  // Here main thread notifies compositor to remove an element from
+  // sIndirectLayerTrees. This removed element might be queried soon.
+  // Checking the elements of sIndirectLayerTrees exist or not before using.
   CompositorLoop()->PostTask(FROM_HERE,
                              NewRunnableFunction(&EraseLayerState, aId));
 }
@@ -1236,9 +1239,15 @@ CrossProcessCompositorParent::AllocPLayerTransactionParent(const nsTArray<Layers
 {
   MOZ_ASSERT(aId != 0);
 
-  if (sIndirectLayerTrees[aId].mLayerManager) {
-    sIndirectLayerTrees[aId].mCrossProcessParent = this;
-    LayerManagerComposite* lm = sIndirectLayerTrees[aId].mLayerManager;
+  CompositorParent::LayerTreeState* state = nullptr;
+  LayerTreeMap::iterator itr = sIndirectLayerTrees.find(aId);
+  if (sIndirectLayerTrees.end() != itr) {
+    state = &itr->second;
+  }
+
+  if (state && state->mLayerManager) {
+    state->mCrossProcessParent = this;
+    LayerManagerComposite* lm = state->mLayerManager;
     *aTextureFactoryIdentifier = lm->GetCompositor()->GetTextureFactoryIdentifier();
     *aSuccess = true;
     LayerTransactionParent* p = new LayerTransactionParent(lm, this, aId);
@@ -1267,7 +1276,13 @@ CrossProcessCompositorParent::DeallocPLayerTransactionParent(PLayerTransactionPa
 bool
 CrossProcessCompositorParent::RecvNotifyChildCreated(const uint64_t& child)
 {
-  sIndirectLayerTrees[child].mParent->NotifyChildCreated(child);
+  const CompositorParent::LayerTreeState* state = CompositorParent::GetIndirectShadowTree(child);
+  if (!state) {
+    return false;
+  }
+
+  MOZ_ASSERT(state->mParent);
+  state->mParent->NotifyChildCreated(child);
   return true;
 }
 
@@ -1281,9 +1296,13 @@ CrossProcessCompositorParent::ShadowLayersUpdated(
   uint64_t id = aLayerTree->GetId();
 
   MOZ_ASSERT(id != 0);
-  MOZ_ASSERT(sIndirectLayerTrees[id].mParent);
 
-  sIndirectLayerTrees[id].mParent->ScheduleRotationOnCompositorThread(aTargetConfig, aIsFirstPaint);
+  const CompositorParent::LayerTreeState* state = CompositorParent::GetIndirectShadowTree(id);
+  if (!state) {
+    return;
+  }
+  MOZ_ASSERT(state->mParent);
+  state->mParent->ScheduleRotationOnCompositorThread(aTargetConfig, aIsFirstPaint);
 
   Layer* shadowRoot = aLayerTree->GetRoot();
   if (shadowRoot) {
@@ -1291,7 +1310,7 @@ CrossProcessCompositorParent::ShadowLayersUpdated(
   }
   UpdateIndirectTree(id, shadowRoot, aTargetConfig);
 
-  sIndirectLayerTrees[id].mParent->NotifyShadowTreeTransaction(id, aIsFirstPaint, aScheduleComposite);
+  state->mParent->NotifyShadowTreeTransaction(id, aIsFirstPaint, aScheduleComposite);
 }
 
 void
@@ -1308,7 +1327,13 @@ CrossProcessCompositorParent::SetTestSampleTime(
 {
   uint64_t id = aLayerTree->GetId();
   MOZ_ASSERT(id != 0);
-  return sIndirectLayerTrees[id].mParent->SetTestSampleTime(aLayerTree, aTime);
+  const CompositorParent::LayerTreeState* state = CompositorParent::GetIndirectShadowTree(id);
+  if (!state) {
+    return false;
+  }
+
+  MOZ_ASSERT(state->mParent);
+  return state->mParent->SetTestSampleTime(aLayerTree, aTime);
 }
 
 void
@@ -1316,14 +1341,26 @@ CrossProcessCompositorParent::LeaveTestMode(LayerTransactionParent* aLayerTree)
 {
   uint64_t id = aLayerTree->GetId();
   MOZ_ASSERT(id != 0);
-  sIndirectLayerTrees[id].mParent->LeaveTestMode(aLayerTree);
+  const CompositorParent::LayerTreeState* state = CompositorParent::GetIndirectShadowTree(id);
+  if (!state) {
+    return;
+  }
+
+  MOZ_ASSERT(state->mParent);
+  state->mParent->LeaveTestMode(aLayerTree);
 }
 
 AsyncCompositionManager*
 CrossProcessCompositorParent::GetCompositionManager(LayerTransactionParent* aLayerTree)
 {
   uint64_t id = aLayerTree->GetId();
-  return sIndirectLayerTrees[id].mParent->GetCompositionManager(aLayerTree);
+  const CompositorParent::LayerTreeState* state = CompositorParent::GetIndirectShadowTree(id);
+  if (!state) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(state->mParent);
+  return state->mParent->GetCompositionManager(aLayerTree);
 }
 
 void