Adding upstream version 115.8.0esr.upstream/115.8.0esr

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

46 files changed, 11332 insertions, 0 deletions

diff --git a/dom/storage/BackgroundSessionStorageServiceParent.cpp b/dom/storage/BackgroundSessionStorageServiceParent.cpp
new file mode 100644
index 0000000000..4182a7a718
--- /dev/null
+++ b/dom/storage/BackgroundSessionStorageServiceParent.cpp
@@ -0,0 +1,29 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "mozilla/dom/BackgroundSessionStorageServiceParent.h"
+
+#include "mozilla/dom/SessionStorageManager.h"
+#include "mozilla/ipc/BackgroundParent.h"
+
+namespace mozilla::dom {
+
+using namespace mozilla::ipc;
+
+mozilla::ipc::IPCResult
+BackgroundSessionStorageServiceParent::RecvClearStoragesForOrigin(
+    const nsACString& aOriginAttrs, const nsACString& aOriginKey) {
+  AssertIsInMainProcess();
+  AssertIsOnBackgroundThread();
+
+  if (!mozilla::dom::RecvClearStoragesForOrigin(aOriginAttrs, aOriginKey)) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+
+  return IPC_OK();
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/storage/BackgroundSessionStorageServiceParent.h b/dom/storage/BackgroundSessionStorageServiceParent.h
new file mode 100644
index 0000000000..ee25dc5c5e
--- /dev/null
+++ b/dom/storage/BackgroundSessionStorageServiceParent.h
@@ -0,0 +1,28 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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 DOM_STORAGE_BACKGROUNDSESSIONSTORAGESERVICEPARENT_H_
+#define DOM_STORAGE_BACKGROUNDSESSIONSTORAGESERVICEPARENT_H_
+
+#include "mozilla/dom/PBackgroundSessionStorageServiceParent.h"
+
+namespace mozilla::dom {
+
+class BackgroundSessionStorageServiceParent final
+    : public PBackgroundSessionStorageServiceParent {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(BackgroundSessionStorageServiceParent, override)
+
+  mozilla::ipc::IPCResult RecvClearStoragesForOrigin(
+      const nsACString& aOriginAttrs, const nsACString& aOriginKey);
+
+ private:
+  ~BackgroundSessionStorageServiceParent() = default;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // DOM_STORAGE_BACKGROUNDSESSIONSTORAGESERVICEPARENT_H_
diff --git a/dom/storage/LocalStorage.cpp b/dom/storage/LocalStorage.cpp
new file mode 100644
index 0000000000..ec75566242
--- /dev/null
+++ b/dom/storage/LocalStorage.cpp
@@ -0,0 +1,216 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "LocalStorage.h"
+#include "LocalStorageCache.h"
+#include "LocalStorageManager.h"
+#include "StorageUtils.h"
+
+#include "nsIPrincipal.h"
+
+#include "mozilla/dom/PermissionMessageUtils.h"
+#include "mozilla/dom/StorageBinding.h"
+#include "mozilla/dom/StorageEvent.h"
+#include "mozilla/dom/StorageEventBinding.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/EnumSet.h"
+#include "nsThreadUtils.h"
+#include "nsContentUtils.h"
+#include "nsServiceManagerUtils.h"
+
+namespace mozilla {
+
+using namespace ipc;
+
+namespace dom {
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(LocalStorage)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(LocalStorage, Storage)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mManager)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_REFERENCE
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(LocalStorage, Storage)
+  CycleCollectionNoteChild(
+      cb, NS_ISUPPORTS_CAST(nsIDOMStorageManager*, tmp->mManager.get()),
+      "mManager");
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(LocalStorage)
+  NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
+NS_INTERFACE_MAP_END_INHERITING(Storage)
+
+NS_IMPL_ADDREF_INHERITED(LocalStorage, Storage)
+NS_IMPL_RELEASE_INHERITED(LocalStorage, Storage)
+
+LocalStorage::LocalStorage(nsPIDOMWindowInner* aWindow,
+                           LocalStorageManager* aManager,
+                           LocalStorageCache* aCache,
+                           const nsAString& aDocumentURI,
+                           nsIPrincipal* aPrincipal,
+                           nsIPrincipal* aStoragePrincipal, bool aIsPrivate)
+    : Storage(aWindow, aPrincipal, aStoragePrincipal),
+      mManager(aManager),
+      mCache(aCache),
+      mDocumentURI(aDocumentURI),
+      mIsPrivate(aIsPrivate) {
+  mCache->Preload();
+}
+
+LocalStorage::~LocalStorage() = default;
+
+int64_t LocalStorage::GetOriginQuotaUsage() const {
+  return mCache->GetOriginQuotaUsage(this);
+}
+
+uint32_t LocalStorage::GetLength(nsIPrincipal& aSubjectPrincipal,
+                                 ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return 0;
+  }
+
+  uint32_t length;
+  aRv = mCache->GetLength(this, &length);
+  return length;
+}
+
+void LocalStorage::Key(uint32_t aIndex, nsAString& aResult,
+                       nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  aRv = mCache->GetKey(this, aIndex, aResult);
+}
+
+void LocalStorage::GetItem(const nsAString& aKey, nsAString& aResult,
+                           nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  aRv = mCache->GetItem(this, aKey, aResult);
+}
+
+void LocalStorage::SetItem(const nsAString& aKey, const nsAString& aData,
+                           nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  nsString data;
+  bool ok = data.Assign(aData, fallible);
+  if (!ok) {
+    aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return;
+  }
+
+  nsString old;
+  aRv = mCache->SetItem(this, aKey, data, old);
+  if (aRv.Failed()) {
+    return;
+  }
+
+  if (!aRv.ErrorCodeIs(NS_SUCCESS_DOM_NO_OPERATION)) {
+    OnChange(aKey, old, aData);
+  }
+}
+
+void LocalStorage::RemoveItem(const nsAString& aKey,
+                              nsIPrincipal& aSubjectPrincipal,
+                              ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  nsAutoString old;
+  aRv = mCache->RemoveItem(this, aKey, old);
+  if (aRv.Failed()) {
+    return;
+  }
+
+  if (!aRv.ErrorCodeIs(NS_SUCCESS_DOM_NO_OPERATION)) {
+    OnChange(aKey, old, VoidString());
+  }
+}
+
+void LocalStorage::Clear(nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  aRv = mCache->Clear(this);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+
+  if (!aRv.ErrorCodeIs(NS_SUCCESS_DOM_NO_OPERATION)) {
+    OnChange(VoidString(), VoidString(), VoidString());
+  }
+}
+
+void LocalStorage::OnChange(const nsAString& aKey, const nsAString& aOldValue,
+                            const nsAString& aNewValue) {
+  NotifyChange(/* aStorage */ this, StoragePrincipal(), aKey, aOldValue,
+               aNewValue, /* aStorageType */ u"localStorage", mDocumentURI,
+               mIsPrivate, /* aImmediateDispatch */ false);
+}
+
+void LocalStorage::ApplyEvent(StorageEvent* aStorageEvent) {
+  MOZ_ASSERT(aStorageEvent);
+
+  nsAutoString key;
+  nsAutoString old;
+  nsAutoString value;
+
+  aStorageEvent->GetKey(key);
+  aStorageEvent->GetNewValue(value);
+
+  // No key means clearing the full storage.
+  if (key.IsVoid()) {
+    MOZ_ASSERT(value.IsVoid());
+    mCache->Clear(this, LocalStorageCache::E10sPropagated);
+    return;
+  }
+
+  // No new value means removing the key.
+  if (value.IsVoid()) {
+    mCache->RemoveItem(this, key, old, LocalStorageCache::E10sPropagated);
+    return;
+  }
+
+  // Otherwise, we set the new value.
+  mCache->SetItem(this, key, value, old, LocalStorageCache::E10sPropagated);
+}
+
+void LocalStorage::GetSupportedNames(nsTArray<nsString>& aKeys) {
+  if (!CanUseStorage(*nsContentUtils::SubjectPrincipal())) {
+    // return just an empty array
+    aKeys.Clear();
+    return;
+  }
+
+  mCache->GetKeys(this, aKeys);
+}
+
+bool LocalStorage::IsForkOf(const Storage* aOther) const {
+  MOZ_ASSERT(aOther);
+  if (aOther->Type() != eLocalStorage) {
+    return false;
+  }
+
+  return mCache == static_cast<const LocalStorage*>(aOther)->mCache;
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/storage/LocalStorage.h b/dom/storage/LocalStorage.h
new file mode 100644
index 0000000000..4df24c5e63
--- /dev/null
+++ b/dom/storage/LocalStorage.h
@@ -0,0 +1,83 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_dom_LocalStorage_h
+#define mozilla_dom_LocalStorage_h
+
+#include "Storage.h"
+#include "nsWeakReference.h"
+
+namespace mozilla::dom {
+
+class LocalStorageCache;
+class LocalStorageManager;
+class StorageEvent;
+
+class LocalStorage final : public Storage, public nsSupportsWeakReference {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(LocalStorage, Storage)
+
+  StorageType Type() const override { return eLocalStorage; }
+
+  LocalStorageManager* GetManager() const { return mManager; }
+
+  LocalStorageCache const* GetCache() const { return mCache; }
+
+  const nsString& DocumentURI() const { return mDocumentURI; }
+
+  LocalStorage(nsPIDOMWindowInner* aWindow, LocalStorageManager* aManager,
+               LocalStorageCache* aCache, const nsAString& aDocumentURI,
+               nsIPrincipal* aPrincipal, nsIPrincipal* aStoragePrincipal,
+               bool aIsPrivate);
+
+  bool IsForkOf(const Storage* aOther) const override;
+
+  // WebIDL
+
+  int64_t GetOriginQuotaUsage() const override;
+
+  uint32_t GetLength(nsIPrincipal& aSubjectPrincipal,
+                     ErrorResult& aRv) override;
+
+  void Key(uint32_t aIndex, nsAString& aResult, nsIPrincipal& aSubjectPrincipal,
+           ErrorResult& aRv) override;
+
+  void GetItem(const nsAString& aKey, nsAString& aResult,
+               nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) override;
+
+  void GetSupportedNames(nsTArray<nsString>& aKeys) override;
+
+  void SetItem(const nsAString& aKey, const nsAString& aValue,
+               nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) override;
+
+  void RemoveItem(const nsAString& aKey, nsIPrincipal& aSubjectPrincipal,
+                  ErrorResult& aRv) override;
+
+  void Clear(nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) override;
+
+  void ApplyEvent(StorageEvent* aStorageEvent);
+
+ private:
+  ~LocalStorage();
+
+  friend class LocalStorageManager;
+  friend class LocalStorageCache;
+
+  RefPtr<LocalStorageManager> mManager;
+  RefPtr<LocalStorageCache> mCache;
+  nsString mDocumentURI;
+
+  // Whether this storage is running in private-browsing window.
+  bool mIsPrivate : 1;
+
+  void OnChange(const nsAString& aKey, const nsAString& aOldValue,
+                const nsAString& aNewValue);
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_LocalStorage_h
diff --git a/dom/storage/LocalStorageCache.cpp b/dom/storage/LocalStorageCache.cpp
new file mode 100644
index 0000000000..4b55482441
--- /dev/null
+++ b/dom/storage/LocalStorageCache.cpp
@@ -0,0 +1,615 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "LocalStorageCache.h"
+
+#include "Storage.h"
+#include "StorageDBThread.h"
+#include "StorageIPC.h"
+#include "StorageUtils.h"
+#include "LocalStorageManager.h"
+
+#include "nsDOMString.h"
+#include "nsXULAppAPI.h"
+#include "mozilla/Unused.h"
+#include "nsProxyRelease.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla::dom {
+
+#define DOM_STORAGE_CACHE_KEEP_ALIVE_TIME_MS 20000
+
+namespace {
+
+const uint32_t kDefaultSet = 0;
+const uint32_t kSessionSet = 1;
+
+inline uint32_t GetDataSetIndex(bool aPrivateBrowsing,
+                                bool aSessionScopedOrLess) {
+  if (!aPrivateBrowsing && aSessionScopedOrLess) {
+    return kSessionSet;
+  }
+
+  return kDefaultSet;
+}
+
+inline uint32_t GetDataSetIndex(const LocalStorage* aStorage) {
+  return GetDataSetIndex(aStorage->IsPrivateBrowsing(),
+                         aStorage->IsSessionScopedOrLess());
+}
+
+}  // namespace
+
+// LocalStorageCacheBridge
+
+NS_IMPL_ADDREF(LocalStorageCacheBridge)
+
+// Since there is no consumer of return value of Release, we can turn this
+// method to void to make implementation of asynchronous
+// LocalStorageCache::Release much simpler.
+NS_IMETHODIMP_(void) LocalStorageCacheBridge::Release(void) {
+  MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");
+  nsrefcnt count = --mRefCnt;
+  NS_LOG_RELEASE(this, count, "LocalStorageCacheBridge");
+  if (0 == count) {
+    mRefCnt = 1; /* stabilize */
+    /* enable this to find non-threadsafe destructors: */
+    /* NS_ASSERT_OWNINGTHREAD(_class); */
+    delete (this);
+  }
+}
+
+// LocalStorageCache
+
+LocalStorageCache::LocalStorageCache(const nsACString* aOriginNoSuffix)
+    : mActor(nullptr),
+      mOriginNoSuffix(*aOriginNoSuffix),
+      mMonitor("LocalStorageCache"),
+      mLoaded(false),
+      mLoadResult(NS_OK),
+      mInitialized(false),
+      mPersistent(false),
+      mPreloadTelemetryRecorded(false) {
+  MOZ_COUNT_CTOR(LocalStorageCache);
+}
+
+LocalStorageCache::~LocalStorageCache() {
+  if (mActor) {
+    mActor->SendDeleteMeInternal();
+    MOZ_ASSERT(!mActor, "SendDeleteMeInternal should have cleared!");
+  }
+
+  if (mManager) {
+    mManager->DropCache(this);
+  }
+
+  MOZ_COUNT_DTOR(LocalStorageCache);
+}
+
+void LocalStorageCache::SetActor(LocalStorageCacheChild* aActor) {
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aActor);
+  MOZ_ASSERT(!mActor);
+
+  mActor = aActor;
+}
+
+NS_IMETHODIMP_(void)
+LocalStorageCache::Release(void) {
+  // We must actually release on the main thread since the cache removes it
+  // self from the manager's hash table.  And we don't want to lock access to
+  // that hash table.
+  if (NS_IsMainThread()) {
+    LocalStorageCacheBridge::Release();
+    return;
+  }
+
+  RefPtr<nsRunnableMethod<LocalStorageCacheBridge, void, false>> event =
+      NewNonOwningRunnableMethod("dom::LocalStorageCacheBridge::Release",
+                                 static_cast<LocalStorageCacheBridge*>(this),
+                                 &LocalStorageCacheBridge::Release);
+
+  nsresult rv = NS_DispatchToMainThread(event);
+  if (NS_FAILED(rv)) {
+    NS_WARNING("LocalStorageCache::Release() on a non-main thread");
+    LocalStorageCacheBridge::Release();
+  }
+}
+
+void LocalStorageCache::Init(LocalStorageManager* aManager, bool aPersistent,
+                             nsIPrincipal* aPrincipal,
+                             const nsACString& aQuotaOriginScope) {
+  MOZ_ASSERT(!aQuotaOriginScope.IsEmpty());
+
+  if (mInitialized) {
+    return;
+  }
+
+  mInitialized = true;
+  aPrincipal->OriginAttributesRef().CreateSuffix(mOriginSuffix);
+  mPrivateBrowsingId = aPrincipal->GetPrivateBrowsingId();
+  mPersistent = aPersistent;
+  mQuotaOriginScope = aQuotaOriginScope;
+
+  if (mPersistent) {
+    mManager = aManager;
+    Preload();
+  }
+
+  // Check the quota string has (or has not) the identical origin suffix as
+  // this storage cache is bound to.
+  MOZ_ASSERT(StringBeginsWith(mQuotaOriginScope, mOriginSuffix));
+  MOZ_ASSERT(mOriginSuffix.IsEmpty() !=
+             StringBeginsWith(mQuotaOriginScope, "^"_ns));
+
+  mUsage = aManager->GetOriginUsage(mQuotaOriginScope, mPrivateBrowsingId);
+}
+
+void LocalStorageCache::NotifyObservers(const LocalStorage* aStorage,
+                                        const nsAString& aKey,
+                                        const nsAString& aOldValue,
+                                        const nsAString& aNewValue) {
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aStorage);
+
+  if (!mActor) {
+    return;
+  }
+
+  // We want to send a message to the parent in order to broadcast the
+  // StorageEvent correctly to any child process.
+
+  Unused << mActor->SendNotify(aStorage->DocumentURI(), aKey, aOldValue,
+                               aNewValue);
+}
+
+inline bool LocalStorageCache::Persist(const LocalStorage* aStorage) const {
+  return mPersistent &&
+         (aStorage->IsPrivateBrowsing() || !aStorage->IsSessionScopedOrLess());
+}
+
+const nsCString LocalStorageCache::Origin() const {
+  return LocalStorageManager::CreateOrigin(mOriginSuffix, mOriginNoSuffix);
+}
+
+LocalStorageCache::Data& LocalStorageCache::DataSet(
+    const LocalStorage* aStorage) {
+  return mData[GetDataSetIndex(aStorage)];
+}
+
+bool LocalStorageCache::ProcessUsageDelta(const LocalStorage* aStorage,
+                                          int64_t aDelta,
+                                          const MutationSource aSource) {
+  return ProcessUsageDelta(GetDataSetIndex(aStorage), aDelta, aSource);
+}
+
+bool LocalStorageCache::ProcessUsageDelta(uint32_t aGetDataSetIndex,
+                                          const int64_t aDelta,
+                                          const MutationSource aSource) {
+  // Check limit per this origin
+  Data& data = mData[aGetDataSetIndex];
+  uint64_t newOriginUsage = data.mOriginQuotaUsage + aDelta;
+  if (aSource == ContentMutation && aDelta > 0 &&
+      newOriginUsage > LocalStorageManager::GetOriginQuota()) {
+    return false;
+  }
+
+  // Now check eTLD+1 limit
+  if (mUsage &&
+      !mUsage->CheckAndSetETLD1UsageDelta(aGetDataSetIndex, aDelta, aSource)) {
+    return false;
+  }
+
+  // Update size in our data set
+  data.mOriginQuotaUsage = newOriginUsage;
+  return true;
+}
+
+void LocalStorageCache::Preload() {
+  if (mLoaded || !mPersistent) {
+    return;
+  }
+
+  StorageDBChild* storageChild =
+      StorageDBChild::GetOrCreate(mPrivateBrowsingId);
+  if (!storageChild) {
+    mLoaded = true;
+    mLoadResult = NS_ERROR_FAILURE;
+    return;
+  }
+
+  storageChild->AsyncPreload(this);
+}
+
+void LocalStorageCache::WaitForPreload(Telemetry::HistogramID aTelemetryID) {
+  if (!mPersistent) {
+    return;
+  }
+
+  bool loaded = mLoaded;
+
+  // Telemetry of rates of pending preloads
+  if (!mPreloadTelemetryRecorded) {
+    mPreloadTelemetryRecorded = true;
+    Telemetry::Accumulate(
+        Telemetry::LOCALDOMSTORAGE_PRELOAD_PENDING_ON_FIRST_ACCESS, !loaded);
+  }
+
+  if (loaded) {
+    return;
+  }
+
+  // Measure which operation blocks and for how long
+  Telemetry::RuntimeAutoTimer timer(aTelemetryID);
+
+  // If preload already started (i.e. we got some first data, but not all)
+  // SyncPreload will just wait for it to finish rather then synchronously
+  // read from the database.  It seems to me more optimal.
+
+  // TODO place for A/B testing (force main thread load vs. let preload finish)
+
+  // No need to check sDatabase for being non-null since preload is either
+  // done before we've shut the DB down or when the DB could not start,
+  // preload has not even be started.
+  StorageDBChild::Get(mPrivateBrowsingId)->SyncPreload(this);
+}
+
+nsresult LocalStorageCache::GetLength(const LocalStorage* aStorage,
+                                      uint32_t* aRetval) {
+  if (Persist(aStorage)) {
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_GETLENGTH_BLOCKING_MS);
+    if (NS_FAILED(mLoadResult)) {
+      return mLoadResult;
+    }
+  }
+
+  *aRetval = DataSet(aStorage).mKeys.Count();
+  return NS_OK;
+}
+
+nsresult LocalStorageCache::GetKey(const LocalStorage* aStorage,
+                                   uint32_t aIndex, nsAString& aRetval) {
+  // XXX: This does a linear search for the key at index, which would
+  // suck if there's a large numer of indexes. Do we care? If so,
+  // maybe we need to have a lazily populated key array here or
+  // something?
+  if (Persist(aStorage)) {
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_GETKEY_BLOCKING_MS);
+    if (NS_FAILED(mLoadResult)) {
+      return mLoadResult;
+    }
+  }
+
+  aRetval.SetIsVoid(true);
+  for (auto iter = DataSet(aStorage).mKeys.Iter(); !iter.Done(); iter.Next()) {
+    if (aIndex == 0) {
+      aRetval = iter.Key();
+      break;
+    }
+    aIndex--;
+  }
+
+  return NS_OK;
+}
+
+void LocalStorageCache::GetKeys(const LocalStorage* aStorage,
+                                nsTArray<nsString>& aKeys) {
+  if (Persist(aStorage)) {
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_GETALLKEYS_BLOCKING_MS);
+  }
+
+  if (NS_FAILED(mLoadResult)) {
+    return;
+  }
+
+  AppendToArray(aKeys, DataSet(aStorage).mKeys.Keys());
+}
+
+nsresult LocalStorageCache::GetItem(const LocalStorage* aStorage,
+                                    const nsAString& aKey, nsAString& aRetval) {
+  if (Persist(aStorage)) {
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_GETVALUE_BLOCKING_MS);
+    if (NS_FAILED(mLoadResult)) {
+      return mLoadResult;
+    }
+  }
+
+  // not using AutoString since we don't want to copy buffer to result
+  nsString value;
+  if (!DataSet(aStorage).mKeys.Get(aKey, &value)) {
+    SetDOMStringToNull(value);
+  }
+
+  aRetval = value;
+
+  return NS_OK;
+}
+
+nsresult LocalStorageCache::SetItem(const LocalStorage* aStorage,
+                                    const nsAString& aKey,
+                                    const nsAString& aValue, nsString& aOld,
+                                    const MutationSource aSource) {
+  // Size of the cache that will change after this action.
+  int64_t delta = 0;
+
+  if (Persist(aStorage)) {
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_SETVALUE_BLOCKING_MS);
+    if (NS_FAILED(mLoadResult)) {
+      return mLoadResult;
+    }
+  }
+
+  Data& data = DataSet(aStorage);
+  if (!data.mKeys.Get(aKey, &aOld)) {
+    SetDOMStringToNull(aOld);
+
+    // We only consider key size if the key doesn't exist before.
+    delta += static_cast<int64_t>(aKey.Length());
+  }
+
+  delta += static_cast<int64_t>(aValue.Length()) -
+           static_cast<int64_t>(aOld.Length());
+
+  if (!ProcessUsageDelta(aStorage, delta, aSource)) {
+    return NS_ERROR_DOM_QUOTA_EXCEEDED_ERR;
+  }
+
+  if (aValue == aOld && DOMStringIsNull(aValue) == DOMStringIsNull(aOld)) {
+    return NS_SUCCESS_DOM_NO_OPERATION;
+  }
+
+  data.mKeys.InsertOrUpdate(aKey, aValue);
+
+  if (aSource != ContentMutation) {
+    return NS_OK;
+  }
+
+#if !defined(MOZ_WIDGET_ANDROID)
+  NotifyObservers(aStorage, aKey, aOld, aValue);
+#endif
+
+  if (Persist(aStorage)) {
+    StorageDBChild* storageChild = StorageDBChild::Get(mPrivateBrowsingId);
+    if (!storageChild) {
+      NS_ERROR(
+          "Writing to localStorage after the database has been shut down"
+          ", data lose!");
+      return NS_ERROR_NOT_INITIALIZED;
+    }
+
+    if (DOMStringIsNull(aOld)) {
+      return storageChild->AsyncAddItem(this, aKey, aValue);
+    }
+
+    return storageChild->AsyncUpdateItem(this, aKey, aValue);
+  }
+
+  return NS_OK;
+}
+
+nsresult LocalStorageCache::RemoveItem(const LocalStorage* aStorage,
+                                       const nsAString& aKey, nsString& aOld,
+                                       const MutationSource aSource) {
+  if (Persist(aStorage)) {
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_REMOVEKEY_BLOCKING_MS);
+    if (NS_FAILED(mLoadResult)) {
+      return mLoadResult;
+    }
+  }
+
+  Data& data = DataSet(aStorage);
+  if (!data.mKeys.Get(aKey, &aOld)) {
+    SetDOMStringToNull(aOld);
+    return NS_SUCCESS_DOM_NO_OPERATION;
+  }
+
+  // Recalculate the cached data size
+  const int64_t delta = -(static_cast<int64_t>(aOld.Length()) +
+                          static_cast<int64_t>(aKey.Length()));
+  Unused << ProcessUsageDelta(aStorage, delta, aSource);
+  data.mKeys.Remove(aKey);
+
+  if (aSource != ContentMutation) {
+    return NS_OK;
+  }
+
+#if !defined(MOZ_WIDGET_ANDROID)
+  NotifyObservers(aStorage, aKey, aOld, VoidString());
+#endif
+
+  if (Persist(aStorage)) {
+    StorageDBChild* storageChild = StorageDBChild::Get(mPrivateBrowsingId);
+    if (!storageChild) {
+      NS_ERROR(
+          "Writing to localStorage after the database has been shut down"
+          ", data lose!");
+      return NS_ERROR_NOT_INITIALIZED;
+    }
+
+    return storageChild->AsyncRemoveItem(this, aKey);
+  }
+
+  return NS_OK;
+}
+
+nsresult LocalStorageCache::Clear(const LocalStorage* aStorage,
+                                  const MutationSource aSource) {
+  bool refresh = false;
+  if (Persist(aStorage)) {
+    // We need to preload all data (know the size) before we can proceeed
+    // to correctly decrease cached usage number.
+    // XXX as in case of unload, this is not technically needed now, but
+    // after super-scope quota introduction we have to do this.  Get telemetry
+    // right now.
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_CLEAR_BLOCKING_MS);
+    if (NS_FAILED(mLoadResult)) {
+      // When we failed to load data from the database, force delete of the
+      // scope data and make use of the storage possible again.
+      refresh = true;
+      mLoadResult = NS_OK;
+    }
+  }
+
+  Data& data = DataSet(aStorage);
+  bool hadData = !!data.mKeys.Count();
+
+  if (hadData) {
+    Unused << ProcessUsageDelta(aStorage, -data.mOriginQuotaUsage, aSource);
+    data.mKeys.Clear();
+  }
+
+  if (aSource != ContentMutation) {
+    return hadData ? NS_OK : NS_SUCCESS_DOM_NO_OPERATION;
+  }
+
+#if !defined(MOZ_WIDGET_ANDROID)
+  if (hadData) {
+    NotifyObservers(aStorage, VoidString(), VoidString(), VoidString());
+  }
+#endif
+
+  if (Persist(aStorage) && (refresh || hadData)) {
+    StorageDBChild* storageChild = StorageDBChild::Get(mPrivateBrowsingId);
+    if (!storageChild) {
+      NS_ERROR(
+          "Writing to localStorage after the database has been shut down"
+          ", data lose!");
+      return NS_ERROR_NOT_INITIALIZED;
+    }
+
+    return storageChild->AsyncClear(this);
+  }
+
+  return hadData ? NS_OK : NS_SUCCESS_DOM_NO_OPERATION;
+}
+
+int64_t LocalStorageCache::GetOriginQuotaUsage(
+    const LocalStorage* aStorage) const {
+  return mData[GetDataSetIndex(aStorage)].mOriginQuotaUsage;
+}
+
+void LocalStorageCache::UnloadItems(uint32_t aUnloadFlags) {
+  if (aUnloadFlags & kUnloadDefault) {
+    // Must wait for preload to pass correct usage to ProcessUsageDelta
+    // XXX this is not technically needed right now since there is just
+    // per-origin isolated quota handling, but when we introduce super-
+    // -scope quotas, we have to do this.  Better to start getting
+    // telemetry right now.
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_UNLOAD_BLOCKING_MS);
+
+    mData[kDefaultSet].mKeys.Clear();
+    ProcessUsageDelta(kDefaultSet, -mData[kDefaultSet].mOriginQuotaUsage);
+  }
+
+  if (aUnloadFlags & kUnloadSession) {
+    mData[kSessionSet].mKeys.Clear();
+    ProcessUsageDelta(kSessionSet, -mData[kSessionSet].mOriginQuotaUsage);
+  }
+
+#ifdef DOM_STORAGE_TESTS
+  if (aUnloadFlags & kTestReload) {
+    WaitForPreload(Telemetry::LOCALDOMSTORAGE_UNLOAD_BLOCKING_MS);
+
+    mData[kDefaultSet].mKeys.Clear();
+    mLoaded = false;  // This is only used in testing code
+    Preload();
+  }
+#endif
+}
+
+// LocalStorageCacheBridge
+
+uint32_t LocalStorageCache::LoadedCount() {
+  MonitorAutoLock monitor(mMonitor);
+  Data& data = mData[kDefaultSet];
+  return data.mKeys.Count();
+}
+
+bool LocalStorageCache::LoadItem(const nsAString& aKey,
+                                 const nsAString& aValue) {
+  MonitorAutoLock monitor(mMonitor);
+  if (mLoaded) {
+    return false;
+  }
+
+  Data& data = mData[kDefaultSet];
+  data.mKeys.LookupOrInsertWith(aKey, [&] {
+    data.mOriginQuotaUsage += aKey.Length() + aValue.Length();
+    return nsString(aValue);
+  });
+  return true;
+}
+
+void LocalStorageCache::LoadDone(nsresult aRv) {
+  MonitorAutoLock monitor(mMonitor);
+  mLoadResult = aRv;
+  mLoaded = true;
+  monitor.Notify();
+}
+
+void LocalStorageCache::LoadWait() {
+  MonitorAutoLock monitor(mMonitor);
+  while (!mLoaded) {
+    monitor.Wait();
+  }
+}
+
+// StorageUsage
+
+StorageUsage::StorageUsage(const nsACString& aOriginScope)
+    : mOriginScope(aOriginScope) {
+  mUsage[kDefaultSet] = mUsage[kSessionSet] = 0LL;
+}
+
+namespace {
+
+class LoadUsageRunnable : public Runnable {
+ public:
+  LoadUsageRunnable(int64_t* aUsage, const int64_t aDelta)
+      : Runnable("dom::LoadUsageRunnable"), mTarget(aUsage), mDelta(aDelta) {}
+
+ private:
+  int64_t* mTarget;
+  int64_t mDelta;
+
+  NS_IMETHOD Run() override {
+    *mTarget = mDelta;
+    return NS_OK;
+  }
+};
+
+}  // namespace
+
+void StorageUsage::LoadUsage(const int64_t aUsage) {
+  // Using kDefaultSet index since it is the index for the persitent data
+  // stored in the database we have just loaded usage for.
+  if (!NS_IsMainThread()) {
+    // In single process scenario we get this call from the DB thread
+    RefPtr<LoadUsageRunnable> r =
+        new LoadUsageRunnable(mUsage + kDefaultSet, aUsage);
+    NS_DispatchToMainThread(r);
+  } else {
+    // On a child process we get this on the main thread already
+    mUsage[kDefaultSet] += aUsage;
+  }
+}
+
+bool StorageUsage::CheckAndSetETLD1UsageDelta(
+    uint32_t aDataSetIndex, const int64_t aDelta,
+    const LocalStorageCache::MutationSource aSource) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  int64_t newUsage = mUsage[aDataSetIndex] + aDelta;
+  if (aSource == LocalStorageCache::ContentMutation && aDelta > 0 &&
+      newUsage > LocalStorageManager::GetSiteQuota()) {
+    return false;
+  }
+
+  mUsage[aDataSetIndex] = newUsage;
+  return true;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/storage/LocalStorageCache.h b/dom/storage/LocalStorageCache.h
new file mode 100644
index 0000000000..9df56cd475
--- /dev/null
+++ b/dom/storage/LocalStorageCache.h
@@ -0,0 +1,306 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_dom_LocalStorageCache_h
+#define mozilla_dom_LocalStorageCache_h
+
+#include "nsIPrincipal.h"
+
+#include "nsString.h"
+#include "nsTHashMap.h"
+#include "nsHashKeys.h"
+#include "mozilla/Monitor.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/Atomics.h"
+
+namespace mozilla::dom {
+
+class LocalStorage;
+class LocalStorageCacheChild;
+class LocalStorageManager;
+class StorageUsage;
+class StorageDBBridge;
+
+// Interface class on which only the database or IPC may call.
+// Used to populate the cache with DB data.
+class LocalStorageCacheBridge {
+ public:
+  NS_IMETHOD_(MozExternalRefCountType) AddRef(void);
+  NS_IMETHOD_(void) Release(void);
+
+  // The origin of the cache, result is concatenation of OriginNoSuffix() and
+  // OriginSuffix(), see below.
+  virtual const nsCString Origin() const = 0;
+
+  // The origin attributes suffix alone, this is usually passed as an
+  // |aOriginSuffix| argument to various methods
+  virtual const nsCString& OriginSuffix() const = 0;
+
+  // The origin in the database usage format (reversed) and without the suffix
+  virtual const nsCString& OriginNoSuffix() const = 0;
+
+  // Whether the cache is already fully loaded
+  virtual bool Loaded() = 0;
+
+  // How many items has so far been loaded into the cache, used
+  // for optimization purposes
+  virtual uint32_t LoadedCount() = 0;
+
+  // Called by the database to load a key and its value to the cache
+  virtual bool LoadItem(const nsAString& aKey, const nsAString& aValue) = 0;
+
+  // Called by the database after all keys and values has been loaded
+  // to this cache
+  virtual void LoadDone(nsresult aRv) = 0;
+
+  // Use to synchronously wait until the cache gets fully loaded with data,
+  // this method exits after LoadDone has been called
+  virtual void LoadWait() = 0;
+
+ protected:
+  virtual ~LocalStorageCacheBridge() = default;
+
+  ThreadSafeAutoRefCnt mRefCnt;
+  NS_DECL_OWNINGTHREAD
+};
+
+// Implementation of scope cache that is responsible for preloading data
+// for persistent storage (localStorage) and hold data for non-private,
+// private and session-only cookie modes.  It is also responsible for
+// persisting data changes using the database, works as a write-back cache.
+class LocalStorageCache : public LocalStorageCacheBridge {
+ public:
+  void AssertIsOnOwningThread() const { NS_ASSERT_OWNINGTHREAD(LocalStorage); }
+
+  void SetActor(LocalStorageCacheChild* aActor);
+
+  void ClearActor() {
+    AssertIsOnOwningThread();
+
+    mActor = nullptr;
+  }
+
+  NS_IMETHOD_(void) Release(void) override;
+
+  enum MutationSource {
+    // The mutation is a result of an explicit JS mutation in this process.
+    // The mutation should be sent to the sDatabase. Quota will be checked and
+    // QuotaExceededError may be returned without the mutation being applied.
+    ContentMutation,
+    // The mutation initially was triggered in a different process and is being
+    // propagated to this cache via LocalStorage::ApplyEvent.  The mutation
+    // should
+    // not be sent to the sDatabase because the originating process is already
+    // doing that.  (In addition to the redundant writes being wasteful, there
+    // is the potential for other processes to see inconsistent state from the
+    // database while preloading.)  Quota will be updated but not checked
+    // because it's assumed it was checked in another process and data-coherency
+    // is more important than slightly exceeding quota.
+    E10sPropagated
+  };
+
+  // Note: We pass aOriginNoSuffix through the ctor here, because
+  // LocalStorageCacheHashKey's ctor is creating this class and
+  // accepts reversed-origin-no-suffix as an argument - the hashing key.
+  explicit LocalStorageCache(const nsACString* aOriginNoSuffix);
+
+ protected:
+  virtual ~LocalStorageCache();
+
+ public:
+  void Init(LocalStorageManager* aManager, bool aPersistent,
+            nsIPrincipal* aPrincipal, const nsACString& aQuotaOriginScope);
+
+  // Get size of per-origin data.
+  int64_t GetOriginQuotaUsage(const LocalStorage* aStorage) const;
+
+  // Starts async preload of this cache if it persistent and not loaded.
+  void Preload();
+
+  // The set of methods that are invoked by DOM storage web API.
+  // We are passing the LocalStorage object just to let the cache
+  // read properties like mPrivate and mSessionOnly.
+  // Get* methods return error when load from the database has failed.
+  nsresult GetLength(const LocalStorage* aStorage, uint32_t* aRetval);
+  nsresult GetKey(const LocalStorage* aStorage, uint32_t index,
+                  nsAString& aRetval);
+  nsresult GetItem(const LocalStorage* aStorage, const nsAString& aKey,
+                   nsAString& aRetval);
+  nsresult SetItem(const LocalStorage* aStorage, const nsAString& aKey,
+                   const nsAString& aValue, nsString& aOld,
+                   const MutationSource aSource = ContentMutation);
+  nsresult RemoveItem(const LocalStorage* aStorage, const nsAString& aKey,
+                      nsString& aOld,
+                      const MutationSource aSource = ContentMutation);
+  nsresult Clear(const LocalStorage* aStorage,
+                 const MutationSource aSource = ContentMutation);
+
+  void GetKeys(const LocalStorage* aStorage, nsTArray<nsString>& aKeys);
+
+  // LocalStorageCacheBridge
+
+  const nsCString Origin() const override;
+  const nsCString& OriginNoSuffix() const override { return mOriginNoSuffix; }
+  const nsCString& OriginSuffix() const override { return mOriginSuffix; }
+  bool Loaded() override { return mLoaded; }
+  uint32_t LoadedCount() override;
+  bool LoadItem(const nsAString& aKey, const nsAString& aValue) override;
+  void LoadDone(nsresult aRv) override;
+  void LoadWait() override;
+
+  // Cache keeps 3 sets of data: regular, private and session-only.
+  // This class keeps keys and values for a set and also caches
+  // size of the data for quick per-origin quota checking.
+  class Data {
+   public:
+    Data() : mOriginQuotaUsage(0) {}
+    int64_t mOriginQuotaUsage;
+    nsTHashMap<nsStringHashKey, nsString> mKeys;
+  };
+
+ public:
+  // Number of data sets we keep: default, session
+  static const uint32_t kDataSetCount = 2;
+
+ private:
+  // API to clear the cache data, this is invoked by chrome operations
+  // like cookie deletion.
+  friend class LocalStorageManager;
+
+  static const uint32_t kUnloadDefault = 1 << 0;
+  static const uint32_t kUnloadSession = 1 << 1;
+  static const uint32_t kUnloadComplete = kUnloadDefault | kUnloadSession;
+
+#ifdef DOM_STORAGE_TESTS
+  static const uint32_t kTestReload = 1 << 15;
+#endif
+
+  void UnloadItems(uint32_t aUnloadFlags);
+
+ private:
+  // Synchronously blocks until the cache is fully loaded from the database
+  void WaitForPreload(mozilla::Telemetry::HistogramID aTelemetryID);
+
+  // Helper to get one of the 3 data sets (regular, private, session)
+  Data& DataSet(const LocalStorage* aStorage);
+
+  // Used for firing storage events and synchronization of caches in other
+  // content processes.
+  void NotifyObservers(const LocalStorage* aStorage, const nsAString& aKey,
+                       const nsAString& aOldValue, const nsAString& aNewValue);
+
+  // Whether the storage change is about to persist
+  bool Persist(const LocalStorage* aStorage) const;
+
+  // Changes the quota usage on the given data set if it fits the quota.
+  // If not, then false is returned and no change to the set must be done.
+  // A special case is if aSource==E10sPropagated, then we will return true even
+  // if the change would put us over quota.  This is done to ensure coherency of
+  // caches between processes in the face of races.  It does allow an attacker
+  // to potentially use N multiples of the quota storage limit if they can
+  // arrange for their origin to execute code in N processes.  However, this is
+  // not considered a particularly concerning threat model because it's already
+  // very possible for a rogue page to attempt to intentionally fill up the
+  // user's storage through the use of multiple domains.
+  bool ProcessUsageDelta(uint32_t aGetDataSetIndex, const int64_t aDelta,
+                         const MutationSource aSource = ContentMutation);
+  bool ProcessUsageDelta(const LocalStorage* aStorage, const int64_t aDelta,
+                         const MutationSource aSource = ContentMutation);
+
+ private:
+  // When a cache is reponsible for its life time (in case of localStorage data
+  // cache) we need to refer our manager since removal of the cache from the
+  // hash table is handled in the destructor by call to the manager.  Cache
+  // could potentially overlive the manager, hence the hard ref.
+  RefPtr<LocalStorageManager> mManager;
+
+  // Reference to the usage counter object we check on for eTLD+1 quota limit.
+  // Obtained from the manager during initialization (Init method).
+  RefPtr<StorageUsage> mUsage;
+
+  // The LocalStorageCacheChild is created at the same time of this class.
+  // In normal operation, the actor will be synchronously cleared in our
+  // destructor when we tell it to delete itself.  In a shutdown-related edge
+  // case in the parent process for JSM's, it is possible for the actor to be
+  // destroyed while this class remains alive, in which case it will be nulled
+  // out.
+  LocalStorageCacheChild* mActor;
+
+  // The origin this cache belongs to in the "DB format", i.e. reversed
+  nsCString mOriginNoSuffix;
+
+  // The origin attributes suffix
+  nsCString mOriginSuffix;
+
+  // The eTLD+1 scope used to count quota usage.  It is in the reversed format
+  // and contains the origin attributes suffix.
+  nsCString mQuotaOriginScope;
+
+  // Non-private Browsing, Private Browsing and Session Only sets.
+  Data mData[kDataSetCount];
+
+  // This monitor is used to wait for full load of data.
+  mozilla::Monitor mMonitor MOZ_UNANNOTATED;
+
+  // Flag that is initially false.  When the cache is about to work with
+  // the database (i.e. it is persistent) this flags is set to true after
+  // all keys and coresponding values are loaded from the database.
+  // This flag never goes from true back to false.  Since this flag is
+  // critical for mData hashtable synchronization, it's made atomic.
+  Atomic<bool, ReleaseAcquire> mLoaded;
+
+  // Result of load from the database.  Valid after mLoaded flag has been set.
+  nsresult mLoadResult;
+
+  // Expected to be only 0 or 1.
+  uint32_t mPrivateBrowsingId;
+
+  // Init() method has been called
+  bool mInitialized : 1;
+
+  // This cache is about to be bound with the database (i.e. it has
+  // to load from the DB first and has to persist when modifying the
+  // default data set.)
+  bool mPersistent : 1;
+
+  // Whether we have already captured state of the cache preload on our first
+  // access.
+  bool mPreloadTelemetryRecorded : 1;
+};
+
+// StorageUsage
+// Infrastructure to manage and check eTLD+1 quota
+class StorageUsageBridge {
+ public:
+  NS_INLINE_DECL_THREADSAFE_VIRTUAL_REFCOUNTING(StorageUsageBridge)
+
+  virtual const nsCString& OriginScope() = 0;
+  virtual void LoadUsage(const int64_t aUsage) = 0;
+
+ protected:
+  // Protected destructor, to discourage deletion outside of Release():
+  virtual ~StorageUsageBridge() = default;
+};
+
+class StorageUsage : public StorageUsageBridge {
+ public:
+  explicit StorageUsage(const nsACString& aOriginScope);
+
+  bool CheckAndSetETLD1UsageDelta(
+      uint32_t aDataSetIndex, int64_t aUsageDelta,
+      const LocalStorageCache::MutationSource aSource);
+
+ private:
+  const nsCString& OriginScope() override { return mOriginScope; }
+  void LoadUsage(const int64_t aUsage) override;
+
+  nsCString mOriginScope;
+  int64_t mUsage[LocalStorageCache::kDataSetCount];
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_LocalStorageCache_h
diff --git a/dom/storage/LocalStorageManager.cpp b/dom/storage/LocalStorageManager.cpp
new file mode 100644
index 0000000000..58b57df76a
--- /dev/null
+++ b/dom/storage/LocalStorageManager.cpp
@@ -0,0 +1,454 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "LocalStorageManager.h"
+#include "LocalStorage.h"
+#include "StorageDBThread.h"
+#include "StorageIPC.h"
+#include "StorageUtils.h"
+
+#include "nsIEffectiveTLDService.h"
+
+#include "nsPIDOMWindow.h"
+#include "nsNetUtil.h"
+#include "nsNetCID.h"
+#include "nsPrintfCString.h"
+#include "nsXULAppAPI.h"
+#include "nsThreadUtils.h"
+#include "nsIObserverService.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/Services.h"
+#include "mozilla/StaticPrefs_dom.h"
+#include "mozilla/dom/LocalStorageCommon.h"
+
+namespace mozilla::dom {
+
+using namespace StorageUtils;
+
+LocalStorageManager* LocalStorageManager::sSelf = nullptr;
+
+// static
+uint32_t LocalStorageManager::GetOriginQuota() {
+  return StaticPrefs::dom_storage_default_quota() * 1024;  // pref is in kBs
+}
+
+// static
+uint32_t LocalStorageManager::GetSiteQuota() {
+  return std::max(StaticPrefs::dom_storage_default_quota(),
+                  StaticPrefs::dom_storage_default_site_quota()) *
+         1024;  // pref is in kBs
+}
+
+NS_IMPL_ISUPPORTS(LocalStorageManager, nsIDOMStorageManager,
+                  nsILocalStorageManager)
+
+LocalStorageManager::LocalStorageManager() : mCaches(8) {
+  MOZ_ASSERT(!NextGenLocalStorageEnabled());
+
+  StorageObserver* observer = StorageObserver::Self();
+  NS_ASSERTION(
+      observer,
+      "No StorageObserver, cannot observe private data delete notifications!");
+
+  if (observer) {
+    observer->AddSink(this);
+  }
+
+  NS_ASSERTION(!sSelf,
+               "Somebody is trying to "
+               "do_CreateInstance(\"@mozilla/dom/localStorage-manager;1\"");
+  sSelf = this;
+
+  if (!XRE_IsParentProcess()) {
+    // Do this only on the child process.  The thread IPC bridge
+    // is also used to communicate chrome observer notifications.
+    // Note: must be called after we set sSelf
+    for (const uint32_t id : {0, 1}) {
+      StorageDBChild::GetOrCreate(id);
+    }
+  }
+}
+
+LocalStorageManager::~LocalStorageManager() {
+  StorageObserver* observer = StorageObserver::Self();
+  if (observer) {
+    observer->RemoveSink(this);
+  }
+
+  sSelf = nullptr;
+}
+
+// static
+nsAutoCString LocalStorageManager::CreateOrigin(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix) {
+  // Note: some hard-coded sqlite statements are dependent on the format this
+  // method returns.  Changing this without updating those sqlite statements
+  // will cause malfunction.
+
+  nsAutoCString scope;
+  scope.Append(aOriginSuffix);
+  scope.Append(':');
+  scope.Append(aOriginNoSuffix);
+  return scope;
+}
+
+LocalStorageCache* LocalStorageManager::GetCache(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix) {
+  CacheOriginHashtable* table = mCaches.GetOrInsertNew(aOriginSuffix);
+  LocalStorageCacheHashKey* entry = table->GetEntry(aOriginNoSuffix);
+  if (!entry) {
+    return nullptr;
+  }
+
+  return entry->cache();
+}
+
+already_AddRefed<StorageUsage> LocalStorageManager::GetOriginUsage(
+    const nsACString& aOriginNoSuffix, const uint32_t aPrivateBrowsingId) {
+  return do_AddRef(mUsages.LookupOrInsertWith(aOriginNoSuffix, [&] {
+    auto usage = MakeRefPtr<StorageUsage>(aOriginNoSuffix);
+
+    StorageDBChild* storageChild =
+        StorageDBChild::GetOrCreate(aPrivateBrowsingId);
+    if (storageChild) {
+      storageChild->AsyncGetUsage(usage);
+    }
+
+    return usage;
+  }));
+}
+
+already_AddRefed<LocalStorageCache> LocalStorageManager::PutCache(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix,
+    const nsACString& aQuotaKey, nsIPrincipal* aPrincipal) {
+  CacheOriginHashtable* table = mCaches.GetOrInsertNew(aOriginSuffix);
+  LocalStorageCacheHashKey* entry = table->PutEntry(aOriginNoSuffix);
+  RefPtr<LocalStorageCache> cache = entry->cache();
+
+  // Lifetime handled by the cache, do persist
+  cache->Init(this, true, aPrincipal, aQuotaKey);
+  return cache.forget();
+}
+
+void LocalStorageManager::DropCache(LocalStorageCache* aCache) {
+  if (!NS_IsMainThread()) {
+    NS_WARNING(
+        "StorageManager::DropCache called on a non-main thread, shutting "
+        "down?");
+  }
+
+  CacheOriginHashtable* table = mCaches.GetOrInsertNew(aCache->OriginSuffix());
+  table->RemoveEntry(aCache->OriginNoSuffix());
+}
+
+nsresult LocalStorageManager::GetStorageInternal(
+    CreateMode aCreateMode, mozIDOMWindow* aWindow, nsIPrincipal* aPrincipal,
+    nsIPrincipal* aStoragePrincipal, const nsAString& aDocumentURI,
+    bool aPrivate, Storage** aRetval) {
+  nsAutoCString originAttrSuffix;
+  nsAutoCString originKey;
+  nsAutoCString quotaKey;
+
+  aStoragePrincipal->OriginAttributesRef().CreateSuffix(originAttrSuffix);
+
+  nsresult rv = aStoragePrincipal->GetStorageOriginKey(originKey);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  rv = aStoragePrincipal->GetLocalStorageQuotaKey(quotaKey);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  RefPtr<LocalStorageCache> cache = GetCache(originAttrSuffix, originKey);
+
+  // Get or create a cache for the given scope
+  if (!cache) {
+    if (aCreateMode == CreateMode::UseIfExistsNeverCreate) {
+      *aRetval = nullptr;
+      return NS_OK;
+    }
+
+    if (aCreateMode == CreateMode::CreateIfShouldPreload) {
+      const uint32_t privateBrowsingId =
+          aStoragePrincipal->GetPrivateBrowsingId();
+
+      // This is a demand to just preload the cache, if the scope has
+      // no data stored, bypass creation and preload of the cache.
+      StorageDBChild* db = StorageDBChild::Get(privateBrowsingId);
+      if (db) {
+        if (!db->ShouldPreloadOrigin(LocalStorageManager::CreateOrigin(
+                originAttrSuffix, originKey))) {
+          return NS_OK;
+        }
+      } else {
+        if (originKey.EqualsLiteral("knalb.:about")) {
+          return NS_OK;
+        }
+      }
+    }
+
+#if !defined(MOZ_WIDGET_ANDROID)
+    ::mozilla::ipc::PBackgroundChild* backgroundActor =
+        ::mozilla::ipc::BackgroundChild::GetOrCreateForCurrentThread();
+    if (NS_WARN_IF(!backgroundActor)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    ::mozilla::ipc::PrincipalInfo principalInfo;
+    rv = mozilla::ipc::PrincipalToPrincipalInfo(aStoragePrincipal,
+                                                &principalInfo);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    uint32_t privateBrowsingId;
+    rv = aStoragePrincipal->GetPrivateBrowsingId(&privateBrowsingId);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+#endif
+
+    // There is always a single instance of a cache per scope
+    // in a single instance of a DOM storage manager.
+    cache = PutCache(originAttrSuffix, originKey, quotaKey, aStoragePrincipal);
+
+#if !defined(MOZ_WIDGET_ANDROID)
+    LocalStorageCacheChild* actor = new LocalStorageCacheChild(cache);
+
+    MOZ_ALWAYS_TRUE(
+        backgroundActor->SendPBackgroundLocalStorageCacheConstructor(
+            actor, principalInfo, originKey, privateBrowsingId));
+
+    cache->SetActor(actor);
+#endif
+  }
+
+  if (aRetval) {
+    nsCOMPtr<nsPIDOMWindowInner> inner = nsPIDOMWindowInner::From(aWindow);
+
+    RefPtr<Storage> storage =
+        new LocalStorage(inner, this, cache, aDocumentURI, aPrincipal,
+                         aStoragePrincipal, aPrivate);
+    storage.forget(aRetval);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+LocalStorageManager::PrecacheStorage(nsIPrincipal* aPrincipal,
+                                     nsIPrincipal* aStoragePrincipal,
+                                     Storage** aRetval) {
+  return GetStorageInternal(CreateMode::CreateIfShouldPreload, nullptr,
+                            aPrincipal, aStoragePrincipal, u""_ns, false,
+                            aRetval);
+}
+
+NS_IMETHODIMP
+LocalStorageManager::CreateStorage(mozIDOMWindow* aWindow,
+                                   nsIPrincipal* aPrincipal,
+                                   nsIPrincipal* aStoragePrincipal,
+                                   const nsAString& aDocumentURI, bool aPrivate,
+                                   Storage** aRetval) {
+  return GetStorageInternal(CreateMode::CreateAlways, aWindow, aPrincipal,
+                            aStoragePrincipal, aDocumentURI, aPrivate, aRetval);
+}
+
+NS_IMETHODIMP
+LocalStorageManager::GetStorage(mozIDOMWindow* aWindow,
+                                nsIPrincipal* aPrincipal,
+                                nsIPrincipal* aStoragePrincipal, bool aPrivate,
+                                Storage** aRetval) {
+  return GetStorageInternal(CreateMode::UseIfExistsNeverCreate, aWindow,
+                            aPrincipal, aStoragePrincipal, u""_ns, aPrivate,
+                            aRetval);
+}
+
+NS_IMETHODIMP
+LocalStorageManager::CloneStorage(Storage* aStorage) {
+  // Cloning is supported only for sessionStorage
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+LocalStorageManager::CheckStorage(nsIPrincipal* aPrincipal, Storage* aStorage,
+                                  bool* aRetval) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aPrincipal);
+  MOZ_ASSERT(aStorage);
+  MOZ_ASSERT(aRetval);
+
+  // Only used by sessionStorage.
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+LocalStorageManager::GetNextGenLocalStorageEnabled(bool* aResult) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aResult);
+
+  *aResult = NextGenLocalStorageEnabled();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+LocalStorageManager::Preload(nsIPrincipal* aPrincipal, JSContext* aContext,
+                             Promise** _retval) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aPrincipal);
+  MOZ_ASSERT(_retval);
+
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+LocalStorageManager::IsPreloaded(nsIPrincipal* aPrincipal, JSContext* aContext,
+                                 Promise** _retval) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aPrincipal);
+  MOZ_ASSERT(_retval);
+
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+LocalStorageManager::GetState(nsIPrincipal* aPrincipal, JSContext* aContext,
+                              Promise** _retval) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aPrincipal);
+  MOZ_ASSERT(_retval);
+
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+void LocalStorageManager::ClearCaches(uint32_t aUnloadFlags,
+                                      const OriginAttributesPattern& aPattern,
+                                      const nsACString& aOriginScope) {
+  for (const auto& cacheEntry : mCaches) {
+    OriginAttributes oa;
+    DebugOnly<bool> rv = oa.PopulateFromSuffix(cacheEntry.GetKey());
+    MOZ_ASSERT(rv);
+    if (!aPattern.Matches(oa)) {
+      // This table doesn't match the given origin attributes pattern
+      continue;
+    }
+
+    CacheOriginHashtable* table = cacheEntry.GetWeak();
+
+    for (auto iter2 = table->Iter(); !iter2.Done(); iter2.Next()) {
+      LocalStorageCache* cache = iter2.Get()->cache();
+
+      if (aOriginScope.IsEmpty() ||
+          StringBeginsWith(cache->OriginNoSuffix(), aOriginScope)) {
+        cache->UnloadItems(aUnloadFlags);
+      }
+    }
+  }
+}
+
+nsresult LocalStorageManager::Observe(const char* aTopic,
+                                      const nsAString& aOriginAttributesPattern,
+                                      const nsACString& aOriginScope) {
+  OriginAttributesPattern pattern;
+  if (!pattern.Init(aOriginAttributesPattern)) {
+    NS_ERROR("Cannot parse origin attributes pattern");
+    return NS_ERROR_FAILURE;
+  }
+
+  // Clear everything, caches + database
+  if (!strcmp(aTopic, "cookie-cleared")) {
+    ClearCaches(LocalStorageCache::kUnloadComplete, pattern, ""_ns);
+    return NS_OK;
+  }
+
+  // Clear everything, caches + database
+  if (!strcmp(aTopic, "extension:purge-localStorage-caches")) {
+    ClearCaches(LocalStorageCache::kUnloadComplete, pattern, aOriginScope);
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "browser:purge-sessionStorage")) {
+    // This is only meant for SessionStorageManager.
+    return NS_OK;
+  }
+
+  // Clear from caches everything that has been stored
+  // while in session-only mode
+  if (!strcmp(aTopic, "session-only-cleared")) {
+    ClearCaches(LocalStorageCache::kUnloadSession, pattern, aOriginScope);
+    return NS_OK;
+  }
+
+  // Clear all private-browsing caches
+  if (!strcmp(aTopic, "private-browsing-data-cleared")) {
+    ClearCaches(LocalStorageCache::kUnloadComplete, pattern, ""_ns);
+    return NS_OK;
+  }
+
+  // Clear localStorage data belonging to an origin pattern
+  if (!strcmp(aTopic, "clear-origin-attributes-data") ||
+      !strcmp(aTopic, "dom-storage:clear-origin-attributes-data")) {
+    ClearCaches(LocalStorageCache::kUnloadComplete, pattern, ""_ns);
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "profile-change")) {
+    // For case caches are still referenced - clear them completely
+    ClearCaches(LocalStorageCache::kUnloadComplete, pattern, ""_ns);
+    mCaches.Clear();
+    return NS_OK;
+  }
+
+#ifdef DOM_STORAGE_TESTS
+  if (!strcmp(aTopic, "test-reload")) {
+    // This immediately completely reloads all caches from the database.
+    ClearCaches(LocalStorageCache::kTestReload, pattern, ""_ns);
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "test-flushed")) {
+    if (!XRE_IsParentProcess()) {
+      nsCOMPtr<nsIObserverService> obs =
+          mozilla::services::GetObserverService();
+      if (obs) {
+        obs->NotifyObservers(nullptr, "domstorage-test-flushed", nullptr);
+      }
+    }
+
+    return NS_OK;
+  }
+#endif
+
+  NS_ERROR("Unexpected topic");
+  return NS_ERROR_UNEXPECTED;
+}
+
+// static
+LocalStorageManager* LocalStorageManager::Self() {
+  MOZ_ASSERT(!NextGenLocalStorageEnabled());
+
+  return sSelf;
+}
+
+LocalStorageManager* LocalStorageManager::Ensure() {
+  MOZ_ASSERT(!NextGenLocalStorageEnabled());
+
+  if (sSelf) {
+    return sSelf;
+  }
+
+  // Cause sSelf to be populated.
+  nsCOMPtr<nsIDOMStorageManager> initializer =
+      do_GetService("@mozilla.org/dom/localStorage-manager;1");
+  MOZ_ASSERT(sSelf, "Didn't initialize?");
+
+  return sSelf;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/storage/LocalStorageManager.h b/dom/storage/LocalStorageManager.h
new file mode 100644
index 0000000000..cffb9c0d76
--- /dev/null
+++ b/dom/storage/LocalStorageManager.h
@@ -0,0 +1,140 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_dom_StorageManager_h
+#define mozilla_dom_StorageManager_h
+
+#include "nsIDOMStorageManager.h"
+#include "nsILocalStorageManager.h"
+#include "StorageObserver.h"
+
+#include "LocalStorage.h"
+#include "LocalStorageCache.h"
+#include "mozilla/dom/Storage.h"
+
+#include "nsTHashtable.h"
+#include "nsClassHashtable.h"
+#include "nsHashKeys.h"
+#include "nsTHashMap.h"
+
+namespace mozilla {
+
+class OriginAttributesPattern;
+
+namespace dom {
+
+class LocalStorageManager final : public nsIDOMStorageManager,
+                                  public nsILocalStorageManager,
+                                  public StorageObserverSink {
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIDOMSTORAGEMANAGER
+  NS_DECL_NSILOCALSTORAGEMANAGER
+
+ public:
+  LocalStorageManager();
+
+  // Reads the preference for DOM storage quota
+  static uint32_t GetOriginQuota();
+
+  // Reads the preference for DOM storage site quota
+  static uint32_t GetSiteQuota();
+
+  // Gets (but not ensures) cache for the given scope
+  LocalStorageCache* GetCache(const nsACString& aOriginSuffix,
+                              const nsACString& aOriginNoSuffix);
+
+  // Returns object keeping usage cache for the scope.
+  already_AddRefed<StorageUsage> GetOriginUsage(
+      const nsACString& aOriginNoSuffix, uint32_t aPrivateBrowsingId);
+
+  static nsAutoCString CreateOrigin(const nsACString& aOriginSuffix,
+                                    const nsACString& aOriginNoSuffix);
+
+ private:
+  ~LocalStorageManager();
+
+  // StorageObserverSink, handler to various chrome clearing notification
+  nsresult Observe(const char* aTopic,
+                   const nsAString& aOriginAttributesPattern,
+                   const nsACString& aOriginScope) override;
+
+  // Since nsTHashtable doesn't like multiple inheritance, we have to aggregate
+  // LocalStorageCache into the entry.
+  class LocalStorageCacheHashKey : public nsCStringHashKey {
+   public:
+    explicit LocalStorageCacheHashKey(const nsACString* aKey)
+        : nsCStringHashKey(aKey), mCache(new LocalStorageCache(aKey)) {}
+
+    LocalStorageCacheHashKey(LocalStorageCacheHashKey&& aOther)
+        : nsCStringHashKey(std::move(aOther)),
+          mCache(std::move(aOther.mCache)),
+          mCacheRef(std::move(aOther.mCacheRef)) {
+      NS_ERROR("Shouldn't be called");
+    }
+
+    LocalStorageCache* cache() { return mCache; }
+    // Keep the cache referenced forever, used for sessionStorage.
+    void HardRef() { mCacheRef = mCache; }
+
+   private:
+    // weak ref only since cache references its manager.
+    LocalStorageCache* mCache;
+    // hard ref when this is sessionStorage to keep it alive forever.
+    RefPtr<LocalStorageCache> mCacheRef;
+  };
+
+  // Ensures cache for a scope, when it doesn't exist it is created and
+  // initalized, this also starts preload of persistent data.
+  already_AddRefed<LocalStorageCache> PutCache(
+      const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix,
+      const nsACString& aQuotaKey, nsIPrincipal* aPrincipal);
+
+  enum class CreateMode {
+    // GetStorage: do not create if it's not already in memory.
+    UseIfExistsNeverCreate,
+    // CreateStorage: Create it if it's not already in memory.
+    CreateAlways,
+    // PrecacheStorage: Create only if the database says we ShouldPreloadOrigin.
+    CreateIfShouldPreload
+  };
+
+  // Helper for creation of DOM storage objects
+  nsresult GetStorageInternal(CreateMode aCreate, mozIDOMWindow* aWindow,
+                              nsIPrincipal* aPrincipal,
+                              nsIPrincipal* aStoragePrincipal,
+                              const nsAString& aDocumentURI, bool aPrivate,
+                              Storage** aRetval);
+
+  // Suffix->origin->cache map
+  using CacheOriginHashtable = nsTHashtable<LocalStorageCacheHashKey>;
+  nsClassHashtable<nsCStringHashKey, CacheOriginHashtable> mCaches;
+
+  void ClearCaches(uint32_t aUnloadFlags,
+                   const OriginAttributesPattern& aPattern,
+                   const nsACString& aKeyPrefix);
+
+  // Global getter of localStorage manager service
+  static LocalStorageManager* Self();
+
+  // Like Self, but creates an instance if we're not yet initialized.
+  static LocalStorageManager* Ensure();
+
+ private:
+  // Keeps usage cache objects for eTLD+1 scopes we have touched.
+  nsTHashMap<nsCString, RefPtr<StorageUsage> > mUsages;
+
+  friend class LocalStorageCache;
+  friend class StorageDBChild;
+  // Releases cache since it is no longer referrered by any Storage object.
+  virtual void DropCache(LocalStorageCache* aCache);
+
+  static LocalStorageManager* sSelf;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_StorageManager_h
diff --git a/dom/storage/PBackgroundLocalStorageCache.ipdl b/dom/storage/PBackgroundLocalStorageCache.ipdl
new file mode 100644
index 0000000000..1a98224016
--- /dev/null
+++ b/dom/storage/PBackgroundLocalStorageCache.ipdl
@@ -0,0 +1,43 @@
+/* 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 protocol PBackground;
+
+include PBackgroundSharedTypes;
+
+namespace mozilla {
+namespace dom {
+
+[ManualDealloc, ChildImpl=virtual, ParentImpl=virtual]
+async protocol PBackgroundLocalStorageCache
+{
+  manager PBackground;
+
+parent:
+  async DeleteMe();
+
+  async Notify(nsString documentURI,
+               nsString key,
+               nsString oldValue,
+               nsString newValue);
+
+child:
+  // The principalInfo and privateBrowsingId could instead be retained by the
+  // LocalStorageCacheChild/LocalStorageCache instead of being re-transmitted.
+  // However, these changes are a temporary optimization intended for uplift,
+  // and this constant factor overhead is very small compared to the upside of
+  // filtering.
+  async Observe(PrincipalInfo principalInfo,
+                PrincipalInfo cachePrincipalInfo,
+                uint32_t privateBrowsingId,
+                nsString documentURI,
+                nsString key,
+                nsString oldValue,
+                nsString newValue);
+
+  async __delete__();
+};
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/storage/PBackgroundSessionStorageCache.ipdl b/dom/storage/PBackgroundSessionStorageCache.ipdl
new file mode 100644
index 0000000000..35f06f43ec
--- /dev/null
+++ b/dom/storage/PBackgroundSessionStorageCache.ipdl
@@ -0,0 +1,75 @@
+/* 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 protocol PBackground;
+include protocol PBackgroundSessionStorageManager;
+include PBackgroundSharedTypes;
+
+namespace mozilla {
+namespace dom {
+
+struct SSSetItemInfo
+{
+  nsString key;
+  nsString value;
+};
+
+struct SSRemoveItemInfo
+{
+  nsString key;
+};
+
+struct SSClearInfo
+{
+};
+
+/**
+ * Union of SessionStorage mutation types.
+ */
+union SSWriteInfo
+{
+  SSSetItemInfo;
+  SSRemoveItemInfo;
+  SSClearInfo;
+};
+
+struct SSCacheCopy {
+  nsCString originKey;
+  PrincipalInfo principalInfo;
+  SSSetItemInfo[] data;
+};
+
+[ChildImpl=virtual, ParentImpl=virtual]
+sync protocol PBackgroundSessionStorageCache
+{
+ manager PBackgroundSessionStorageManager;
+
+ parent:
+  async DeleteMe();
+
+  /**
+    * Copy SessionStorageCache from the parent process to the content process.
+    * See SessionStorageManager documentation for more details.
+    *
+    * This needs to be synchronous because SessionStorage's semantics are
+    * synchronous. Note that the BackgroundSessionStorageManager in the
+    * PBackground parent already has the answers to this request immediately
+    * available without needing to consult any other threads or perform any I/O.
+    */
+  sync Load()
+       returns (SSSetItemInfo[] aData);
+
+  /**
+   * Send changes for SessionStorageCache from a content process to the parent
+   * process so that the data in the parent can be updated to be in sync with
+   * the content. See SessionStorageManager documentation for more details.
+   */
+  async Checkpoint(SSWriteInfo[] aWriteInfos);
+
+ child:
+   async __delete__();
+};
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/storage/PBackgroundSessionStorageManager.ipdl b/dom/storage/PBackgroundSessionStorageManager.ipdl
new file mode 100644
index 0000000000..50041c78f7
--- /dev/null
+++ b/dom/storage/PBackgroundSessionStorageManager.ipdl
@@ -0,0 +1,37 @@
+/* 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 protocol PBackground;
+include protocol PBackgroundSessionStorageCache;
+include PBackgroundSharedTypes;
+
+include "mozilla/dom/quota/SerializationHelpers.h";
+
+using mozilla::OriginAttributesPattern
+  from "mozilla/OriginAttributes.h";
+
+namespace mozilla {
+namespace dom {
+
+[ChildImpl=virtual, ParentImpl=virtual]
+sync protocol PBackgroundSessionStorageManager
+{
+ manager PBackground;
+ manages PBackgroundSessionStorageCache;
+
+ parent:
+  async PBackgroundSessionStorageCache(PrincipalInfo aPrincipalInfo, nsCString aOriginKey);
+
+  async ClearStorages(OriginAttributesPattern aPattern, nsCString aOriginScope);
+
+  async DeleteMe();
+
+ child:
+  async __delete__();
+
+  async ClearStoragesForOrigin(nsCString aOriginAttrs, nsCString aOriginKey);
+};
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/storage/PBackgroundSessionStorageService.ipdl b/dom/storage/PBackgroundSessionStorageService.ipdl
new file mode 100644
index 0000000000..ef6087f0c3
--- /dev/null
+++ b/dom/storage/PBackgroundSessionStorageService.ipdl
@@ -0,0 +1,22 @@
+/* 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 protocol PBackground;
+
+namespace mozilla {
+namespace dom {
+
+[ChildImpl="SessionStorageService"]
+protocol PBackgroundSessionStorageService
+{
+  manager PBackground;
+
+ parent:
+  async __delete__();
+
+  async ClearStoragesForOrigin(nsCString originAttrs, nsCString originKey);
+};
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/storage/PBackgroundStorage.ipdl b/dom/storage/PBackgroundStorage.ipdl
new file mode 100644
index 0000000000..44e7c8a612
--- /dev/null
+++ b/dom/storage/PBackgroundStorage.ipdl
@@ -0,0 +1,70 @@
+/* -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil; tab-width: 8 -*- */
+/* vim: set sw=4 ts=8 et tw=80 ft=cpp : */
+/* 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 protocol PBackground;
+
+include "mozilla/dom/quota/SerializationHelpers.h";
+
+using mozilla::OriginAttributesPattern
+  from "mozilla/OriginAttributes.h";
+
+namespace mozilla {
+namespace dom {
+
+/* This protocol bridges async access to the database thread running on the
+ * parent process and caches running on the child process.
+ */
+[ManualDealloc, ChildImpl=virtual, ParentImpl=virtual]
+sync protocol PBackgroundStorage
+{
+  manager PBackground;
+
+parent:
+  async DeleteMe();
+
+  sync Preload(nsCString originSuffix,
+               nsCString originNoSuffix,
+               uint32_t alreadyLoadedCount)
+    returns (nsString[] keys, nsString[] values, nsresult rv);
+
+  async AsyncPreload(nsCString originSuffix, nsCString originNoSuffix,
+                     bool priority);
+  async AsyncGetUsage(nsCString scope);
+  async AsyncAddItem(nsCString originSuffix, nsCString originNoSuffix,
+                     nsString key, nsString value);
+  async AsyncUpdateItem(nsCString originSuffix, nsCString originNoSuffix,
+                        nsString key, nsString value);
+  async AsyncRemoveItem(nsCString originSuffix, nsCString originNoSuffix,
+                        nsString key);
+  async AsyncClear(nsCString originSuffix, nsCString originNoSuffix);
+  async AsyncFlush();
+
+  // These are privileged operations for use only by the observer API for
+  // delayed initialization and clearing origins and will never be used from
+  // content process children.  Ideally these would be guarded by checks or
+  // exist on a separate, privileged interface, but PBackgroundStorage is
+  // already insecure.
+  async Startup();
+  async ClearAll();
+  async ClearMatchingOrigin(nsCString originNoSuffix);
+  async ClearMatchingOriginAttributes(OriginAttributesPattern pattern);
+
+child:
+  async __delete__();
+
+  async Observe(nsCString topic,
+                nsString originAttributesPattern,
+                nsCString originScope);
+  async OriginsHavingData(nsCString[] origins);
+  async LoadItem(nsCString originSuffix, nsCString originNoSuffix, nsString key,
+                 nsString value);
+  async LoadDone(nsCString originSuffix, nsCString originNoSuffix, nsresult rv);
+  async LoadUsage(nsCString scope, int64_t usage);
+  async Error(nsresult rv);
+};
+
+}
+}
diff --git a/dom/storage/PSessionStorageObserver.ipdl b/dom/storage/PSessionStorageObserver.ipdl
new file mode 100644
index 0000000000..ad223346db
--- /dev/null
+++ b/dom/storage/PSessionStorageObserver.ipdl
@@ -0,0 +1,42 @@
+/* -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil; tab-width: 8 -*- */
+/* vim: set sw=4 ts=8 et tw=80 ft=cpp : */
+/* 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 protocol PContent;
+
+namespace mozilla {
+namespace dom {
+
+/**
+ * Protocol used to relay chrome observer notifications related to clearing data
+ * to SessionStorageManager instances in content processes. A single instance is
+ * created by each content process when LocalStorage NextGen is enabled. When
+ * LSNG is disabled, the notifications are instead propagated via
+ * PBackgroundStorageChild. This does mean there are potentially slight ordering
+ * differences in when the notification will be received and processed. It's
+ * okay for this protocol to be managed by PContent rather than PBackground
+ * because these notifications are both rare and to-child-only. (Legacy
+ * LocalStorage was moved to PBackground from PContent because of parent-process
+ * main-thread contention for the processing of "parent:" messages in a very
+ * performance-sensitive context!)
+ */
+[ManualDealloc, ChildImpl=virtual, ParentImpl=virtual]
+async protocol PSessionStorageObserver
+{
+  manager PContent;
+
+parent:
+  async DeleteMe();
+
+child:
+  async __delete__();
+
+  async Observe(nsCString topic,
+                nsString originAttributesPattern,
+                nsCString originScope);
+};
+
+}
+}
diff --git a/dom/storage/PartitionedLocalStorage.cpp b/dom/storage/PartitionedLocalStorage.cpp
new file mode 100644
index 0000000000..847d578668
--- /dev/null
+++ b/dom/storage/PartitionedLocalStorage.cpp
@@ -0,0 +1,133 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "PartitionedLocalStorage.h"
+#include "SessionStorageCache.h"
+#include "nsContentUtils.h"
+
+#include "mozilla/dom/StorageBinding.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_INHERITED(PartitionedLocalStorage, Storage);
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(PartitionedLocalStorage)
+NS_INTERFACE_MAP_END_INHERITING(Storage)
+
+NS_IMPL_ADDREF_INHERITED(PartitionedLocalStorage, Storage)
+NS_IMPL_RELEASE_INHERITED(PartitionedLocalStorage, Storage)
+
+PartitionedLocalStorage::PartitionedLocalStorage(
+    nsPIDOMWindowInner* aWindow, nsIPrincipal* aPrincipal,
+    nsIPrincipal* aStoragePrincipal, SessionStorageCache* aCache)
+    : Storage(aWindow, aPrincipal, aStoragePrincipal), mCache(aCache) {}
+
+PartitionedLocalStorage::~PartitionedLocalStorage() = default;
+
+int64_t PartitionedLocalStorage::GetOriginQuotaUsage() const {
+  return mCache->GetOriginQuotaUsage();
+}
+
+uint32_t PartitionedLocalStorage::GetLength(nsIPrincipal& aSubjectPrincipal,
+                                            ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return 0;
+  }
+
+  return mCache->Length();
+}
+
+void PartitionedLocalStorage::Key(uint32_t aIndex, nsAString& aResult,
+                                  nsIPrincipal& aSubjectPrincipal,
+                                  ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  mCache->Key(aIndex, aResult);
+}
+
+void PartitionedLocalStorage::GetItem(const nsAString& aKey, nsAString& aResult,
+                                      nsIPrincipal& aSubjectPrincipal,
+                                      ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  mCache->GetItem(aKey, aResult);
+}
+
+void PartitionedLocalStorage::GetSupportedNames(nsTArray<nsString>& aKeys) {
+  if (!CanUseStorage(*nsContentUtils::SubjectPrincipal())) {
+    // return just an empty array
+    aKeys.Clear();
+    return;
+  }
+
+  mCache->GetKeys(aKeys);
+}
+
+void PartitionedLocalStorage::SetItem(const nsAString& aKey,
+                                      const nsAString& aValue,
+                                      nsIPrincipal& aSubjectPrincipal,
+                                      ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  nsString oldValue;
+  nsresult rv = mCache->SetItem(aKey, aValue, oldValue);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    aRv.Throw(rv);
+    return;
+  }
+
+  if (rv == NS_SUCCESS_DOM_NO_OPERATION) {
+    return;
+  }
+}
+
+void PartitionedLocalStorage::RemoveItem(const nsAString& aKey,
+                                         nsIPrincipal& aSubjectPrincipal,
+                                         ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  nsString oldValue;
+  nsresult rv = mCache->RemoveItem(aKey, oldValue);
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+
+  if (rv == NS_SUCCESS_DOM_NO_OPERATION) {
+    return;
+  }
+}
+
+void PartitionedLocalStorage::Clear(nsIPrincipal& aSubjectPrincipal,
+                                    ErrorResult& aRv) {
+  uint32_t length = GetLength(aSubjectPrincipal, aRv);
+  if (!length) {
+    return;
+  }
+
+  mCache->Clear();
+}
+
+bool PartitionedLocalStorage::IsForkOf(const Storage* aOther) const {
+  MOZ_ASSERT(aOther);
+  if (aOther->Type() != eLocalStorage) {
+    return false;
+  }
+
+  return mCache == static_cast<const PartitionedLocalStorage*>(aOther)->mCache;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/storage/PartitionedLocalStorage.h b/dom/storage/PartitionedLocalStorage.h
new file mode 100644
index 0000000000..6be4a6a7ab
--- /dev/null
+++ b/dom/storage/PartitionedLocalStorage.h
@@ -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=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_dom_PartitionedLocalStorage_h
+#define mozilla_dom_PartitionedLocalStorage_h
+
+#include "Storage.h"
+
+class nsIPrincipal;
+
+namespace mozilla::dom {
+
+class SessionStorageCache;
+
+// PartitionedLocalStorage is a in-memory-only storage exposed to trackers. It
+// doesn't share data with other contexts.
+
+class PartitionedLocalStorage final : public Storage {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(PartitionedLocalStorage, Storage)
+
+  PartitionedLocalStorage(nsPIDOMWindowInner* aWindow, nsIPrincipal* aPrincipal,
+                          nsIPrincipal* aStoragePrincipal,
+                          SessionStorageCache* aCache);
+
+  StorageType Type() const override { return ePartitionedLocalStorage; }
+
+  int64_t GetOriginQuotaUsage() const override;
+
+  bool IsForkOf(const Storage* aStorage) const override;
+
+  // WebIDL
+  uint32_t GetLength(nsIPrincipal& aSubjectPrincipal,
+                     ErrorResult& aRv) override;
+
+  void Key(uint32_t aIndex, nsAString& aResult, nsIPrincipal& aSubjectPrincipal,
+           ErrorResult& aRv) override;
+
+  void GetItem(const nsAString& aKey, nsAString& aResult,
+               nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) override;
+
+  void GetSupportedNames(nsTArray<nsString>& aKeys) override;
+
+  void SetItem(const nsAString& aKey, const nsAString& aValue,
+               nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) override;
+
+  void RemoveItem(const nsAString& aKey, nsIPrincipal& aSubjectPrincipal,
+                  ErrorResult& aRv) override;
+
+  void Clear(nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) override;
+
+ private:
+  ~PartitionedLocalStorage();
+
+  RefPtr<SessionStorageCache> mCache;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_PartitionedLocalStorage_h
diff --git a/dom/storage/SessionStorage.cpp b/dom/storage/SessionStorage.cpp
new file mode 100644
index 0000000000..4f13370338
--- /dev/null
+++ b/dom/storage/SessionStorage.cpp
@@ -0,0 +1,258 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "SessionStorage.h"
+
+#include "SessionStorageCache.h"
+#include "SessionStorageManager.h"
+
+#include "mozilla/dom/StorageBinding.h"
+#include "mozilla/Preferences.h"
+#include "nsContentUtils.h"
+#include "nsIPrincipal.h"
+#include "nsPIDOMWindow.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_INHERITED(SessionStorage, Storage, mManager);
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(SessionStorage)
+NS_INTERFACE_MAP_END_INHERITING(Storage)
+
+NS_IMPL_ADDREF_INHERITED(SessionStorage, Storage)
+NS_IMPL_RELEASE_INHERITED(SessionStorage, Storage)
+
+SessionStorage::SessionStorage(nsPIDOMWindowInner* aWindow,
+                               nsIPrincipal* aPrincipal,
+                               nsIPrincipal* aStoragePrincipal,
+                               SessionStorageCache* aCache,
+                               SessionStorageManager* aManager,
+                               const nsAString& aDocumentURI, bool aIsPrivate)
+    : Storage(aWindow, aPrincipal, aStoragePrincipal),
+      mCache(aCache),
+      mManager(aManager),
+      mDocumentURI(aDocumentURI),
+      mIsPrivate(aIsPrivate),
+      mHasPendingStableStateCallback(false) {
+  MOZ_ASSERT(aCache);
+}
+
+SessionStorage::~SessionStorage() = default;
+
+int64_t SessionStorage::GetOriginQuotaUsage() const {
+  nsresult rv = EnsureCacheLoadedOrCloned();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return 0;
+  }
+
+  return mCache->GetOriginQuotaUsage();
+}
+
+uint32_t SessionStorage::GetLength(nsIPrincipal& aSubjectPrincipal,
+                                   ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return 0;
+  }
+
+  nsresult rv = EnsureCacheLoadedOrCloned();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    aRv.Throw(rv);
+    return 0;
+  }
+
+  return mCache->Length();
+}
+
+void SessionStorage::Key(uint32_t aIndex, nsAString& aResult,
+                         nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  nsresult rv = EnsureCacheLoadedOrCloned();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    aRv.Throw(rv);
+    return;
+  }
+
+  mCache->Key(aIndex, aResult);
+}
+
+void SessionStorage::GetItem(const nsAString& aKey, nsAString& aResult,
+                             nsIPrincipal& aSubjectPrincipal,
+                             ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  nsresult rv = EnsureCacheLoadedOrCloned();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    aRv.Throw(rv);
+    return;
+  }
+
+  mCache->GetItem(aKey, aResult);
+}
+
+void SessionStorage::GetSupportedNames(nsTArray<nsString>& aKeys) {
+  if (!CanUseStorage(*nsContentUtils::SubjectPrincipal())) {
+    // return just an empty array
+    aKeys.Clear();
+    return;
+  }
+
+  nsresult rv = EnsureCacheLoadedOrCloned();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    // return just an empty array
+    aKeys.Clear();
+    return;
+  }
+
+  mCache->GetKeys(aKeys);
+}
+
+void SessionStorage::SetItem(const nsAString& aKey, const nsAString& aValue,
+                             nsIPrincipal& aSubjectPrincipal,
+                             ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  nsresult rv = EnsureCacheLoadedOrCloned();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    aRv.Throw(rv);
+    return;
+  }
+
+  nsString oldValue;
+  rv = mCache->SetItem(aKey, aValue, oldValue);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    aRv.Throw(rv);
+    return;
+  }
+
+  if (rv == NS_SUCCESS_DOM_NO_OPERATION) {
+    return;
+  }
+
+  BroadcastChangeNotification(aKey, oldValue, aValue);
+}
+
+void SessionStorage::RemoveItem(const nsAString& aKey,
+                                nsIPrincipal& aSubjectPrincipal,
+                                ErrorResult& aRv) {
+  if (!CanUseStorage(aSubjectPrincipal)) {
+    aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
+    return;
+  }
+
+  nsresult rv = EnsureCacheLoadedOrCloned();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    aRv.Throw(rv);
+    return;
+  }
+
+  nsString oldValue;
+  rv = mCache->RemoveItem(aKey, oldValue);
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+
+  if (rv == NS_SUCCESS_DOM_NO_OPERATION) {
+    return;
+  }
+
+  BroadcastChangeNotification(aKey, oldValue, VoidString());
+}
+
+void SessionStorage::Clear(nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) {
+  uint32_t length = GetLength(aSubjectPrincipal, aRv);
+  if (!length) {
+    return;
+  }
+
+  nsresult rv = EnsureCacheLoadedOrCloned();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    aRv.Throw(rv);
+    return;
+  }
+
+  mCache->Clear();
+  BroadcastChangeNotification(VoidString(), VoidString(), VoidString());
+}
+
+void SessionStorage::BroadcastChangeNotification(const nsAString& aKey,
+                                                 const nsAString& aOldValue,
+                                                 const nsAString& aNewValue) {
+  NotifyChange(this, StoragePrincipal(), aKey, aOldValue, aNewValue,
+               u"sessionStorage", mDocumentURI, mIsPrivate, false);
+
+  // Sync changes on SessionStorageCache at the next statble state.
+  if (mManager->CanLoadData()) {
+    MaybeScheduleStableStateCallback();
+  }
+}
+
+bool SessionStorage::IsForkOf(const Storage* aOther) const {
+  MOZ_ASSERT(aOther);
+  if (aOther->Type() != eSessionStorage) {
+    return false;
+  }
+
+  return mCache == static_cast<const SessionStorage*>(aOther)->mCache;
+}
+
+void SessionStorage::MaybeScheduleStableStateCallback() {
+  AssertIsOnOwningThread();
+
+  if (!mHasPendingStableStateCallback) {
+    nsContentUtils::RunInStableState(
+        NewRunnableMethod("SessionStorage::StableStateCallback", this,
+                          &SessionStorage::StableStateCallback));
+
+    mHasPendingStableStateCallback = true;
+  }
+}
+
+void SessionStorage::StableStateCallback() {
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mHasPendingStableStateCallback);
+  MOZ_ASSERT(mManager);
+  MOZ_ASSERT(mCache);
+
+  mHasPendingStableStateCallback = false;
+
+  if (mManager->CanLoadData()) {
+    mManager->CheckpointData(*StoragePrincipal(), *mCache);
+  }
+}
+
+nsresult SessionStorage::EnsureCacheLoadedOrCloned() const {
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mManager);
+
+  if (!mManager->CanLoadData()) {
+    return NS_OK;
+  }
+
+  // Ensure manager actor.
+  nsresult rv = mManager->EnsureManager();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // Ensure cache is loaded or cloned.
+  if (mCache->WasLoadedOrCloned()) {
+    return NS_OK;
+  }
+
+  return mManager->LoadData(*StoragePrincipal(), *mCache);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/storage/SessionStorage.h b/dom/storage/SessionStorage.h
new file mode 100644
index 0000000000..de20282276
--- /dev/null
+++ b/dom/storage/SessionStorage.h
@@ -0,0 +1,86 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_dom_SessionStorage_h
+#define mozilla_dom_SessionStorage_h
+
+#include "Storage.h"
+
+class nsIPrincipal;
+
+namespace mozilla::dom {
+
+class SessionStorageCache;
+class SessionStorageManager;
+
+class SessionStorage final : public Storage {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(SessionStorage, Storage)
+
+  SessionStorage(nsPIDOMWindowInner* aWindow, nsIPrincipal* aPrincipal,
+                 nsIPrincipal* aStoragePrincipal, SessionStorageCache* aCache,
+                 SessionStorageManager* aManager, const nsAString& aDocumentURI,
+                 bool aIsPrivate);
+
+  void AssertIsOnOwningThread() const {
+    NS_ASSERT_OWNINGTHREAD(SessionStorage);
+  }
+
+  StorageType Type() const override { return eSessionStorage; }
+
+  SessionStorageManager* Manager() const { return mManager; }
+
+  SessionStorageCache* Cache() const { return mCache; }
+
+  int64_t GetOriginQuotaUsage() const override;
+
+  bool IsForkOf(const Storage* aStorage) const override;
+
+  // WebIDL
+  uint32_t GetLength(nsIPrincipal& aSubjectPrincipal,
+                     ErrorResult& aRv) override;
+
+  void Key(uint32_t aIndex, nsAString& aResult, nsIPrincipal& aSubjectPrincipal,
+           ErrorResult& aRv) override;
+
+  void GetItem(const nsAString& aKey, nsAString& aResult,
+               nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) override;
+
+  void GetSupportedNames(nsTArray<nsString>& aKeys) override;
+
+  void SetItem(const nsAString& aKey, const nsAString& aValue,
+               nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) override;
+
+  void RemoveItem(const nsAString& aKey, nsIPrincipal& aSubjectPrincipal,
+                  ErrorResult& aRv) override;
+
+  void Clear(nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) override;
+
+ private:
+  ~SessionStorage();
+
+  void BroadcastChangeNotification(const nsAString& aKey,
+                                   const nsAString& aOldValue,
+                                   const nsAString& aNewValue);
+
+  void MaybeScheduleStableStateCallback();
+
+  void StableStateCallback();
+
+  nsresult EnsureCacheLoadedOrCloned() const;
+
+  RefPtr<SessionStorageCache> mCache;
+  RefPtr<SessionStorageManager> mManager;
+
+  nsString mDocumentURI;
+  bool mIsPrivate;
+  bool mHasPendingStableStateCallback;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_SessionStorage_h
diff --git a/dom/storage/SessionStorageCache.cpp b/dom/storage/SessionStorageCache.cpp
new file mode 100644
index 0000000000..40f29ebc26
--- /dev/null
+++ b/dom/storage/SessionStorageCache.cpp
@@ -0,0 +1,292 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "SessionStorageCache.h"
+
+#include "LocalStorageManager.h"
+#include "StorageIPC.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/dom/LSWriteOptimizer.h"
+#include "mozilla/dom/PBackgroundSessionStorageCache.h"
+#include "nsDOMString.h"
+
+namespace mozilla::dom {
+
+void SSWriteOptimizer::Enumerate(nsTArray<SSWriteInfo>& aWriteInfos) {
+  AssertIsOnOwningThread();
+
+  // The mWriteInfos hash table contains all write infos, but it keeps them in
+  // an arbitrary order, which means write infos need to be sorted before being
+  // processed.
+
+  nsTArray<NotNull<WriteInfo*>> writeInfos;
+  GetSortedWriteInfos(writeInfos);
+
+  for (const auto& writeInfo : writeInfos) {
+    switch (writeInfo->GetType()) {
+      case WriteInfo::InsertItem: {
+        const auto& insertItemInfo =
+            static_cast<const InsertItemInfo&>(*writeInfo);
+
+        aWriteInfos.AppendElement(
+            SSSetItemInfo{nsString{insertItemInfo.GetKey()},
+                          nsString{insertItemInfo.GetValue()}});
+
+        break;
+      }
+
+      case WriteInfo::UpdateItem: {
+        const auto& updateItemInfo =
+            static_cast<const UpdateItemInfo&>(*writeInfo);
+
+        if (updateItemInfo.UpdateWithMove()) {
+          // See the comment in LSWriteOptimizer::InsertItem for more details
+          // about the UpdateWithMove flag.
+
+          aWriteInfos.AppendElement(
+              SSRemoveItemInfo{nsString{updateItemInfo.GetKey()}});
+        }
+
+        aWriteInfos.AppendElement(
+            SSSetItemInfo{nsString{updateItemInfo.GetKey()},
+                          nsString{updateItemInfo.GetValue()}});
+
+        break;
+      }
+
+      case WriteInfo::DeleteItem: {
+        const auto& deleteItemInfo =
+            static_cast<const DeleteItemInfo&>(*writeInfo);
+
+        aWriteInfos.AppendElement(
+            SSRemoveItemInfo{nsString{deleteItemInfo.GetKey()}});
+
+        break;
+      }
+
+      case WriteInfo::Truncate: {
+        aWriteInfos.AppendElement(SSClearInfo{});
+
+        break;
+      }
+
+      default:
+        MOZ_CRASH("Bad type!");
+    }
+  }
+}
+
+SessionStorageCache::SessionStorageCache()
+    : mActor(nullptr), mLoadedOrCloned(false) {}
+
+SessionStorageCache::~SessionStorageCache() {
+  if (mActor) {
+    mActor->SendDeleteMeInternal();
+    MOZ_ASSERT(!mActor, "SendDeleteMeInternal should have cleared!");
+  }
+}
+
+int64_t SessionStorageCache::GetOriginQuotaUsage() {
+  return mDataSet.mOriginQuotaUsage;
+}
+
+uint32_t SessionStorageCache::Length() { return mDataSet.mKeys.Count(); }
+
+void SessionStorageCache::Key(uint32_t aIndex, nsAString& aResult) {
+  aResult.SetIsVoid(true);
+  for (auto iter = mDataSet.mKeys.ConstIter(); !iter.Done(); iter.Next()) {
+    if (aIndex == 0) {
+      aResult = iter.Key();
+      return;
+    }
+    aIndex--;
+  }
+}
+
+void SessionStorageCache::GetItem(const nsAString& aKey, nsAString& aResult) {
+  // not using AutoString since we don't want to copy buffer to result
+  nsString value;
+  if (!mDataSet.mKeys.Get(aKey, &value)) {
+    SetDOMStringToNull(value);
+  }
+  aResult = value;
+}
+
+void SessionStorageCache::GetKeys(nsTArray<nsString>& aKeys) {
+  AppendToArray(aKeys, mDataSet.mKeys.Keys());
+}
+
+nsresult SessionStorageCache::SetItem(const nsAString& aKey,
+                                      const nsAString& aValue,
+                                      nsString& aOldValue,
+                                      bool aRecordWriteInfo) {
+  int64_t delta = 0;
+
+  if (!mDataSet.mKeys.Get(aKey, &aOldValue)) {
+    SetDOMStringToNull(aOldValue);
+
+    // We only consider key size if the key doesn't exist before.
+    delta = static_cast<int64_t>(aKey.Length());
+  }
+
+  delta += static_cast<int64_t>(aValue.Length()) -
+           static_cast<int64_t>(aOldValue.Length());
+
+  if (aValue == aOldValue &&
+      DOMStringIsNull(aValue) == DOMStringIsNull(aOldValue)) {
+    return NS_SUCCESS_DOM_NO_OPERATION;
+  }
+
+  if (!mDataSet.ProcessUsageDelta(delta)) {
+    return NS_ERROR_DOM_QUOTA_EXCEEDED_ERR;
+  }
+
+  if (aRecordWriteInfo && XRE_IsContentProcess()) {
+    if (DOMStringIsNull(aOldValue)) {
+      mDataSet.mWriteOptimizer.InsertItem(aKey, aValue);
+    } else {
+      mDataSet.mWriteOptimizer.UpdateItem(aKey, aValue);
+    }
+  }
+
+  mDataSet.mKeys.InsertOrUpdate(aKey, nsString(aValue));
+  return NS_OK;
+}
+
+nsresult SessionStorageCache::RemoveItem(const nsAString& aKey,
+                                         nsString& aOldValue,
+                                         bool aRecordWriteInfo) {
+  if (!mDataSet.mKeys.Get(aKey, &aOldValue)) {
+    return NS_SUCCESS_DOM_NO_OPERATION;
+  }
+
+  // Recalculate the cached data size
+  mDataSet.ProcessUsageDelta(-(static_cast<int64_t>(aOldValue.Length()) +
+                               static_cast<int64_t>(aKey.Length())));
+
+  if (aRecordWriteInfo && XRE_IsContentProcess()) {
+    mDataSet.mWriteOptimizer.DeleteItem(aKey);
+  }
+
+  mDataSet.mKeys.Remove(aKey);
+  return NS_OK;
+}
+
+void SessionStorageCache::Clear(bool aByUserInteraction,
+                                bool aRecordWriteInfo) {
+  mDataSet.ProcessUsageDelta(-mDataSet.mOriginQuotaUsage);
+
+  if (aRecordWriteInfo && XRE_IsContentProcess()) {
+    mDataSet.mWriteOptimizer.Truncate();
+  }
+
+  mDataSet.mKeys.Clear();
+}
+
+void SessionStorageCache::ResetWriteInfos() {
+  mDataSet.mWriteOptimizer.Reset();
+}
+
+already_AddRefed<SessionStorageCache> SessionStorageCache::Clone() const {
+  RefPtr<SessionStorageCache> cache = new SessionStorageCache();
+
+  cache->mDataSet.mOriginQuotaUsage = mDataSet.mOriginQuotaUsage;
+  for (const auto& keyEntry : mDataSet.mKeys) {
+    cache->mDataSet.mKeys.InsertOrUpdate(keyEntry.GetKey(), keyEntry.GetData());
+    cache->mDataSet.mWriteOptimizer.InsertItem(keyEntry.GetKey(),
+                                               keyEntry.GetData());
+  }
+
+  return cache.forget();
+}
+
+nsTArray<SSSetItemInfo> SessionStorageCache::SerializeData() {
+  nsTArray<SSSetItemInfo> data;
+  for (const auto& keyEntry : mDataSet.mKeys) {
+    data.EmplaceBack(nsString{keyEntry.GetKey()}, keyEntry.GetData());
+  }
+  return data;
+}
+
+nsTArray<SSWriteInfo> SessionStorageCache::SerializeWriteInfos() {
+  nsTArray<SSWriteInfo> writeInfos;
+  mDataSet.mWriteOptimizer.Enumerate(writeInfos);
+  return writeInfos;
+}
+
+void SessionStorageCache::DeserializeData(
+    const nsTArray<SSSetItemInfo>& aData) {
+  Clear(false, /* aRecordWriteInfo */ false);
+  for (const auto& keyValuePair : aData) {
+    nsString oldValue;
+    SetItem(keyValuePair.key(), keyValuePair.value(), oldValue, false);
+  }
+}
+
+void SessionStorageCache::DeserializeWriteInfos(
+    const nsTArray<SSWriteInfo>& aInfos) {
+  for (const auto& writeInfo : aInfos) {
+    switch (writeInfo.type()) {
+      case SSWriteInfo::TSSSetItemInfo: {
+        const SSSetItemInfo& info = writeInfo.get_SSSetItemInfo();
+
+        nsString oldValue;
+        SetItem(info.key(), info.value(), oldValue,
+                /* aRecordWriteInfo */ false);
+
+        break;
+      }
+
+      case SSWriteInfo::TSSRemoveItemInfo: {
+        const SSRemoveItemInfo& info = writeInfo.get_SSRemoveItemInfo();
+
+        nsString oldValue;
+        RemoveItem(info.key(), oldValue,
+                   /* aRecordWriteInfo */ false);
+
+        break;
+      }
+
+      case SSWriteInfo::TSSClearInfo: {
+        Clear(false, /* aRecordWriteInfo */ false);
+
+        break;
+      }
+
+      default:
+        MOZ_CRASH("Should never get here!");
+    }
+  }
+}
+
+void SessionStorageCache::SetActor(SessionStorageCacheChild* aActor) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(aActor);
+  MOZ_ASSERT(!mActor);
+
+  mActor = aActor;
+}
+
+void SessionStorageCache::ClearActor() {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(mActor);
+
+  mActor = nullptr;
+}
+
+bool SessionStorageCache::DataSet::ProcessUsageDelta(int64_t aDelta) {
+  // Check limit per this origin
+  uint64_t newOriginUsage = mOriginQuotaUsage + aDelta;
+  if (aDelta > 0 && newOriginUsage > LocalStorageManager::GetOriginQuota()) {
+    return false;
+  }
+
+  // Update size in our data set
+  mOriginQuotaUsage = newOriginUsage;
+  return true;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/storage/SessionStorageCache.h b/dom/storage/SessionStorageCache.h
new file mode 100644
index 0000000000..6e5a57d3da
--- /dev/null
+++ b/dom/storage/SessionStorageCache.h
@@ -0,0 +1,99 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_dom_SessionStorageCache_h
+#define mozilla_dom_SessionStorageCache_h
+
+#include "mozilla/UniquePtr.h"
+#include "mozilla/dom/LSWriteOptimizerImpl.h"
+#include "nsTHashMap.h"
+
+namespace mozilla::dom {
+
+class SSSetItemInfo;
+class SSWriteInfo;
+class SessionStorageCacheChild;
+
+/**
+ * Coalescing manipulation queue used by `SessionStorageCache`.  Used by
+ * `SessionStorageCache` to buffer and coalesce manipulations before they
+ * are sent to the parent process.
+ */
+class SSWriteOptimizer final : public LSWriteOptimizer<nsAString, nsString> {
+ public:
+  void Enumerate(nsTArray<SSWriteInfo>& aWriteInfos);
+};
+
+class SessionStorageCache final {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(SessionStorageCache)
+
+  SessionStorageCache();
+
+  int64_t GetOriginQuotaUsage();
+
+  uint32_t Length();
+
+  void Key(uint32_t aIndex, nsAString& aResult);
+
+  void GetItem(const nsAString& aKey, nsAString& aResult);
+
+  void GetKeys(nsTArray<nsString>& aKeys);
+
+  nsresult SetItem(const nsAString& aKey, const nsAString& aValue,
+                   nsString& aOldValue, bool aRecordWriteInfo = true);
+
+  nsresult RemoveItem(const nsAString& aKey, nsString& aOldValue,
+                      bool aRecordWriteInfo = true);
+
+  void Clear(bool aByUserInteraction = true, bool aRecordWriteInfo = true);
+
+  void ResetWriteInfos();
+
+  already_AddRefed<SessionStorageCache> Clone() const;
+
+  nsTArray<SSSetItemInfo> SerializeData();
+
+  nsTArray<SSWriteInfo> SerializeWriteInfos();
+
+  void DeserializeData(const nsTArray<SSSetItemInfo>& aData);
+
+  void DeserializeWriteInfos(const nsTArray<SSWriteInfo>& aInfos);
+
+  void SetActor(SessionStorageCacheChild* aActor);
+
+  SessionStorageCacheChild* Actor() const { return mActor; }
+
+  void ClearActor();
+
+  void SetLoadedOrCloned() { mLoadedOrCloned = true; }
+
+  bool WasLoadedOrCloned() const { return mLoadedOrCloned; }
+
+ private:
+  ~SessionStorageCache();
+
+  struct DataSet {
+    DataSet() : mOriginQuotaUsage(0) {}
+
+    bool ProcessUsageDelta(int64_t aDelta);
+
+    nsTHashMap<nsStringHashKey, nsString> mKeys;
+
+    SSWriteOptimizer mWriteOptimizer;
+
+    int64_t mOriginQuotaUsage;
+  };
+
+  DataSet mDataSet;
+
+  SessionStorageCacheChild* mActor;
+  bool mLoadedOrCloned;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_SessionStorageCache_h
diff --git a/dom/storage/SessionStorageManager.cpp b/dom/storage/SessionStorageManager.cpp
new file mode 100644
index 0000000000..020083730a
--- /dev/null
+++ b/dom/storage/SessionStorageManager.cpp
@@ -0,0 +1,987 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "SessionStorageManager.h"
+
+#include "StorageIPC.h"
+#include "SessionStorage.h"
+#include "SessionStorageCache.h"
+#include "SessionStorageObserver.h"
+#include "StorageUtils.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/OriginAttributes.h"
+#include "mozilla/PrincipalHashKey.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/StoragePrincipalHelper.h"
+#include "mozilla/dom/CanonicalBrowsingContext.h"
+#include "mozilla/dom/ContentChild.h"
+#include "mozilla/dom/LocalStorageCommon.h"
+#include "mozilla/dom/PBackgroundSessionStorageCache.h"
+#include "mozilla/dom/PBackgroundSessionStorageManager.h"
+#include "mozilla/dom/PermissionMessageUtils.h"
+#include "mozilla/dom/WindowGlobalParent.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/ipc/BackgroundParent.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "nsTHashMap.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla::dom {
+
+using namespace StorageUtils;
+
+// Parent process, background thread hashmap that stores top context id and
+// manager pair.
+static StaticAutoPtr<
+    nsRefPtrHashtable<nsUint64HashKey, BackgroundSessionStorageManager>>
+    sManagers;
+
+bool RecvShutdownBackgroundSessionStorageManagers() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  sManagers = nullptr;
+  return true;
+}
+
+void RecvPropagateBackgroundSessionStorageManager(
+    uint64_t aCurrentTopContextId, uint64_t aTargetTopContextId) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  if (sManagers) {
+    if (RefPtr<BackgroundSessionStorageManager> mgr =
+            sManagers->Get(aCurrentTopContextId)) {
+      mgr->MaybeDispatchSessionStoreUpdate();
+      mgr->SetCurrentBrowsingContextId(aTargetTopContextId);
+      // Because of bfcache, we may re-register aTargetTopContextId in
+      // CanonicalBrowsingContext::ReplacedBy.
+      // XXXBFCache do we want to tweak this behavior and ensure this is
+      // called only once?
+      sManagers->InsertOrUpdate(aTargetTopContextId, std::move(mgr));
+    }
+  }
+}
+
+bool RecvRemoveBackgroundSessionStorageManager(uint64_t aTopContextId) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  if (sManagers) {
+    RefPtr<BackgroundSessionStorageManager> mgr;
+    sManagers->Remove(aTopContextId, getter_AddRefs(mgr));
+
+    if (mgr) {
+      mgr->CancelSessionStoreUpdate();
+    }
+  }
+
+  return true;
+}
+
+bool RecvLoadSessionStorageData(
+    uint64_t aTopContextId,
+    nsTArray<mozilla::dom::SSCacheCopy>&& aCacheCopyList) {
+  if (aCacheCopyList.IsEmpty()) {
+    return true;
+  }
+
+  RefPtr<BackgroundSessionStorageManager> manager =
+      BackgroundSessionStorageManager::GetOrCreate(aTopContextId);
+
+  if (!manager) {
+    return true;
+  }
+
+  for (const auto& cacheInit : aCacheCopyList) {
+    OriginAttributes attrs;
+    StoragePrincipalHelper::GetOriginAttributes(cacheInit.principalInfo(),
+                                                attrs);
+
+    nsAutoCString originAttrs;
+    attrs.CreateSuffix(originAttrs);
+
+    manager->UpdateData(originAttrs, cacheInit.originKey(), cacheInit.data());
+  }
+
+  return true;
+}
+
+bool RecvGetSessionStorageData(
+    uint64_t aTopContextId, uint32_t aSizeLimit, bool aCancelSessionStoreTimer,
+    ::mozilla::ipc::PBackgroundParent::GetSessionStorageManagerDataResolver&&
+        aResolver) {
+  nsTArray<mozilla::dom::SSCacheCopy> data;
+  auto resolve = MakeScopeExit([&]() { aResolver(std::move(data)); });
+
+  if (!sManagers) {
+    return true;
+  }
+
+  RefPtr<BackgroundSessionStorageManager> manager =
+      sManagers->Get(aTopContextId);
+  if (!manager) {
+    return true;
+  }
+
+  if (aCancelSessionStoreTimer) {
+    manager->CancelSessionStoreUpdate();
+  }
+
+  manager->GetData(aSizeLimit, data);
+
+  return true;
+}
+
+bool RecvClearStoragesForOrigin(const nsACString& aOriginAttrs,
+                                const nsACString& aOriginKey) {
+  mozilla::ipc::AssertIsInMainProcess();
+  mozilla::ipc::AssertIsOnBackgroundThread();
+
+  if (!sManagers) {
+    return true;
+  }
+
+  for (auto& entry : *sManagers) {
+    entry.GetData()->ClearStoragesForOrigin(aOriginAttrs, aOriginKey);
+  }
+
+  return true;
+}
+
+void SessionStorageManagerBase::ClearStoragesInternal(
+    const OriginAttributesPattern& aPattern, const nsACString& aOriginScope) {
+  for (const auto& oaEntry : mOATable) {
+    OriginAttributes oa;
+    DebugOnly<bool> ok = oa.PopulateFromSuffix(oaEntry.GetKey());
+    MOZ_ASSERT(ok);
+    if (!aPattern.Matches(oa)) {
+      // This table doesn't match the given origin attributes pattern
+      continue;
+    }
+
+    OriginKeyHashTable* table = oaEntry.GetWeak();
+    for (const auto& originKeyEntry : *table) {
+      if (aOriginScope.IsEmpty() ||
+          StringBeginsWith(originKeyEntry.GetKey(), aOriginScope)) {
+        const auto cache = originKeyEntry.GetData()->mCache;
+        cache->Clear(false);
+        cache->ResetWriteInfos();
+      }
+    }
+  }
+}
+
+void SessionStorageManagerBase::ClearStoragesForOriginInternal(
+    const nsACString& aOriginAttrs, const nsACString& aOriginKey) {
+  for (const auto& oaEntry : mOATable) {
+    // Filter tables which match the given origin attrs.
+    if (oaEntry.GetKey() != aOriginAttrs) {
+      continue;
+    }
+
+    OriginKeyHashTable* table = oaEntry.GetWeak();
+    for (const auto& originKeyEntry : *table) {
+      // Match exact origin (without origin attrs).
+      if (originKeyEntry.GetKey() != aOriginKey) {
+        continue;
+      }
+
+      const auto cache = originKeyEntry.GetData()->mCache;
+      cache->Clear(false);
+      cache->ResetWriteInfos();
+    }
+  }
+}
+
+SessionStorageManagerBase::OriginRecord*
+SessionStorageManagerBase::GetOriginRecord(
+    const nsACString& aOriginAttrs, const nsACString& aOriginKey,
+    const bool aMakeIfNeeded, SessionStorageCache* const aCloneFrom) {
+  // XXX It seems aMakeIfNeeded is always known at compile-time, so this could
+  // be split into two functions.
+
+  if (aMakeIfNeeded) {
+    return mOATable.GetOrInsertNew(aOriginAttrs)
+        ->LookupOrInsertWith(
+            aOriginKey,
+            [&] {
+              auto newOriginRecord = MakeUnique<OriginRecord>();
+              if (aCloneFrom) {
+                newOriginRecord->mCache = aCloneFrom->Clone();
+              } else {
+                newOriginRecord->mCache = new SessionStorageCache();
+              }
+              return newOriginRecord;
+            })
+        .get();
+  }
+
+  auto* const table = mOATable.Get(aOriginAttrs);
+  if (!table) return nullptr;
+
+  return table->Get(aOriginKey);
+}
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(SessionStorageManager)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+  NS_INTERFACE_MAP_ENTRY(nsIDOMStorageManager)
+  NS_INTERFACE_MAP_ENTRY(nsIDOMSessionStorageManager)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION(SessionStorageManager, mBrowsingContext)
+NS_IMPL_CYCLE_COLLECTING_ADDREF(SessionStorageManager)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(SessionStorageManager)
+
+SessionStorageManager::SessionStorageManager(
+    RefPtr<BrowsingContext> aBrowsingContext)
+    : mBrowsingContext(std::move(aBrowsingContext)), mActor(nullptr) {
+  AssertIsOnMainThread();
+
+  StorageObserver* observer = StorageObserver::Self();
+  NS_ASSERTION(
+      observer,
+      "No StorageObserver, cannot observe private data delete notifications!");
+
+  if (observer) {
+    observer->AddSink(this);
+  }
+
+  if (!XRE_IsParentProcess() && NextGenLocalStorageEnabled()) {
+    // When LSNG is enabled the thread IPC bridge doesn't exist, so we have to
+    // create own protocol to distribute chrome observer notifications to
+    // content processes.
+    mObserver = SessionStorageObserver::Get();
+
+    if (!mObserver) {
+      ContentChild* contentActor = ContentChild::GetSingleton();
+      MOZ_ASSERT(contentActor);
+
+      RefPtr<SessionStorageObserver> observer = new SessionStorageObserver();
+
+      SessionStorageObserverChild* actor =
+          new SessionStorageObserverChild(observer);
+
+      MOZ_ALWAYS_TRUE(
+          contentActor->SendPSessionStorageObserverConstructor(actor));
+
+      observer->SetActor(actor);
+
+      mObserver = std::move(observer);
+    }
+  }
+}
+
+SessionStorageManager::~SessionStorageManager() {
+  StorageObserver* observer = StorageObserver::Self();
+  if (observer) {
+    observer->RemoveSink(this);
+  }
+
+  if (mActor) {
+    mActor->SendDeleteMeInternal();
+    MOZ_ASSERT(!mActor, "SendDeleteMeInternal should have cleared!");
+  }
+}
+
+bool SessionStorageManager::CanLoadData() {
+  AssertIsOnMainThread();
+
+  return mBrowsingContext && !mBrowsingContext->IsDiscarded();
+}
+
+void SessionStorageManager::SetActor(SessionStorageManagerChild* aActor) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(aActor);
+  MOZ_ASSERT(!mActor);
+
+  mActor = aActor;
+}
+
+bool SessionStorageManager::ActorExists() const {
+  AssertIsOnMainThread();
+
+  return mActor;
+}
+
+void SessionStorageManager::ClearActor() {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(mActor);
+
+  mActor = nullptr;
+}
+
+nsresult SessionStorageManager::EnsureManager() {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(CanLoadData());
+
+  if (ActorExists()) {
+    return NS_OK;
+  }
+
+  ::mozilla::ipc::PBackgroundChild* backgroundActor =
+      ::mozilla::ipc::BackgroundChild::GetOrCreateForCurrentThread();
+  if (NS_WARN_IF(!backgroundActor)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  RefPtr<SessionStorageManagerChild> actor =
+      new SessionStorageManagerChild(this);
+
+  if (!backgroundActor->SendPBackgroundSessionStorageManagerConstructor(
+          actor, mBrowsingContext->Top()->Id())) {
+    return NS_ERROR_FAILURE;
+  }
+
+  SetActor(actor);
+
+  return NS_OK;
+}
+
+SessionStorageCacheChild* SessionStorageManager::EnsureCache(
+    nsIPrincipal& aPrincipal, const nsACString& aOriginKey,
+    SessionStorageCache& aCache) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(CanLoadData());
+  MOZ_ASSERT(ActorExists());
+
+  if (aCache.Actor()) {
+    return aCache.Actor();
+  }
+
+  mozilla::ipc::PrincipalInfo info;
+  nsresult rv = PrincipalToPrincipalInfo(&aPrincipal, &info);
+
+  if (NS_FAILED(rv)) {
+    return nullptr;
+  }
+
+  RefPtr<SessionStorageCacheChild> actor =
+      new SessionStorageCacheChild(&aCache);
+  if (!mActor->SendPBackgroundSessionStorageCacheConstructor(actor, info,
+                                                             aOriginKey)) {
+    return nullptr;
+  }
+
+  aCache.SetActor(actor);
+
+  return actor;
+}
+
+nsresult SessionStorageManager::LoadData(nsIPrincipal& aPrincipal,
+                                         SessionStorageCache& aCache) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(mActor);
+
+  nsAutoCString originKey;
+  nsresult rv = aPrincipal.GetStorageOriginKey(originKey);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  nsAutoCString originAttributes;
+  aPrincipal.OriginAttributesRef().CreateSuffix(originAttributes);
+
+  auto* const originRecord =
+      GetOriginRecord(originAttributes, originKey, true, nullptr);
+  MOZ_ASSERT(originRecord);
+
+  if (originRecord->mLoaded) {
+    return NS_OK;
+  }
+
+  RefPtr<SessionStorageCacheChild> cacheActor =
+      EnsureCache(aPrincipal, originKey, aCache);
+
+  if (!cacheActor) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsTArray<SSSetItemInfo> data;
+  if (!cacheActor->SendLoad(&data)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  originRecord->mCache->DeserializeData(data);
+
+  originRecord->mLoaded.Flip();
+  aCache.SetLoadedOrCloned();
+
+  return NS_OK;
+}
+
+void SessionStorageManager::CheckpointData(nsIPrincipal& aPrincipal,
+                                           SessionStorageCache& aCache) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(mActor);
+
+  nsAutoCString originKey;
+  nsresult rv = aPrincipal.GetStorageOriginKey(originKey);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return;
+  }
+
+  return CheckpointDataInternal(aPrincipal, originKey, aCache);
+}
+
+void SessionStorageManager::CheckpointDataInternal(
+    nsIPrincipal& aPrincipal, const nsACString& aOriginKey,
+    SessionStorageCache& aCache) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(mActor);
+
+  nsTArray<SSWriteInfo> writeInfos = aCache.SerializeWriteInfos();
+
+  if (writeInfos.IsEmpty()) {
+    return;
+  }
+
+  RefPtr<SessionStorageCacheChild> cacheActor =
+      EnsureCache(aPrincipal, aOriginKey, aCache);
+
+  if (!cacheActor) {
+    return;
+  }
+
+  Unused << cacheActor->SendCheckpoint(writeInfos);
+
+  aCache.ResetWriteInfos();
+}
+
+nsresult SessionStorageManager::ClearStoragesForOrigin(
+    const nsACString& aOriginAttrs, const nsACString& aOriginKey) {
+  AssertIsOnMainThread();
+
+  ClearStoragesForOriginInternal(aOriginAttrs, aOriginKey);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+SessionStorageManager::PrecacheStorage(nsIPrincipal* aPrincipal,
+                                       nsIPrincipal* aStoragePrincipal,
+                                       Storage** aRetval) {
+  // Nothing to preload.
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+SessionStorageManager::GetSessionStorageCache(
+    nsIPrincipal* aPrincipal, nsIPrincipal* aStoragePrincipal,
+    RefPtr<SessionStorageCache>* aRetVal) {
+  return GetSessionStorageCacheHelper(aStoragePrincipal, true, nullptr,
+                                      aRetVal);
+}
+
+nsresult SessionStorageManager::GetSessionStorageCacheHelper(
+    nsIPrincipal* aPrincipal, bool aMakeIfNeeded,
+    SessionStorageCache* aCloneFrom, RefPtr<SessionStorageCache>* aRetVal) {
+  nsAutoCString originKey;
+  nsAutoCString originAttributes;
+  nsresult rv = aPrincipal->GetStorageOriginKey(originKey);
+  aPrincipal->OriginAttributesRef().CreateSuffix(originAttributes);
+  if (NS_FAILED(rv)) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  return GetSessionStorageCacheHelper(originAttributes, originKey,
+                                      aMakeIfNeeded, aCloneFrom, aRetVal);
+}
+
+nsresult SessionStorageManager::GetSessionStorageCacheHelper(
+    const nsACString& aOriginAttrs, const nsACString& aOriginKey,
+    bool aMakeIfNeeded, SessionStorageCache* aCloneFrom,
+    RefPtr<SessionStorageCache>* aRetVal) {
+  if (OriginRecord* const originRecord = GetOriginRecord(
+          aOriginAttrs, aOriginKey, aMakeIfNeeded, aCloneFrom)) {
+    *aRetVal = originRecord->mCache;
+  } else {
+    *aRetVal = nullptr;
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+SessionStorageManager::CreateStorage(mozIDOMWindow* aWindow,
+                                     nsIPrincipal* aPrincipal,
+                                     nsIPrincipal* aStoragePrincipal,
+                                     const nsAString& aDocumentURI,
+                                     bool aPrivate, Storage** aRetval) {
+  RefPtr<SessionStorageCache> cache;
+  nsresult rv = GetSessionStorageCache(aPrincipal, aStoragePrincipal, &cache);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  nsCOMPtr<nsPIDOMWindowInner> inner = nsPIDOMWindowInner::From(aWindow);
+
+  RefPtr<SessionStorage> storage =
+      new SessionStorage(inner, aPrincipal, aStoragePrincipal, cache, this,
+                         aDocumentURI, aPrivate);
+
+  storage.forget(aRetval);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+SessionStorageManager::GetStorage(mozIDOMWindow* aWindow,
+                                  nsIPrincipal* aPrincipal,
+                                  nsIPrincipal* aStoragePrincipal,
+                                  bool aPrivate, Storage** aRetval) {
+  *aRetval = nullptr;
+
+  RefPtr<SessionStorageCache> cache;
+  nsresult rv =
+      GetSessionStorageCacheHelper(aStoragePrincipal, false, nullptr, &cache);
+  if (NS_FAILED(rv) || !cache) {
+    return rv;
+  }
+
+  nsCOMPtr<nsPIDOMWindowInner> inner = nsPIDOMWindowInner::From(aWindow);
+
+  RefPtr<SessionStorage> storage = new SessionStorage(
+      inner, aPrincipal, aStoragePrincipal, cache, this, u""_ns, aPrivate);
+
+  storage.forget(aRetval);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+SessionStorageManager::CloneStorage(Storage* aStorage) {
+  if (NS_WARN_IF(!aStorage)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  if (aStorage->Type() != Storage::eSessionStorage) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  // ToDo: At the moment, we clone the cache on the child process and then
+  // send the checkpoint.  It would be nicer if we either serailizing all the
+  // data and sync to the parent process directly or clonig storage on the
+  // parnet process and sync it to the child process on demand.
+
+  RefPtr<SessionStorageCache> cache;
+  nsresult rv = GetSessionStorageCacheHelper(
+      aStorage->StoragePrincipal(), true,
+      static_cast<SessionStorage*>(aStorage)->Cache(), &cache);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // If cache was cloned from other storage, then we shouldn't load the cache
+  // at the first access.
+  cache->SetLoadedOrCloned();
+
+  if (CanLoadData()) {
+    rv = EnsureManager();
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    CheckpointData(*aStorage->StoragePrincipal(), *cache);
+  }
+
+  return rv;
+}
+
+NS_IMETHODIMP
+SessionStorageManager::CheckStorage(nsIPrincipal* aPrincipal, Storage* aStorage,
+                                    bool* aRetval) {
+  if (NS_WARN_IF(!aStorage)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  if (!aPrincipal) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  *aRetval = false;
+
+  RefPtr<SessionStorageCache> cache;
+  nsresult rv =
+      GetSessionStorageCacheHelper(aPrincipal, false, nullptr, &cache);
+  if (NS_FAILED(rv) || !cache) {
+    return rv;
+  }
+
+  if (aStorage->Type() != Storage::eSessionStorage) {
+    return NS_OK;
+  }
+
+  RefPtr<SessionStorage> sessionStorage =
+      static_cast<SessionStorage*>(aStorage);
+  if (sessionStorage->Cache() != cache) {
+    return NS_OK;
+  }
+
+  if (!StorageUtils::PrincipalsEqual(aStorage->StoragePrincipal(),
+                                     aPrincipal)) {
+    return NS_OK;
+  }
+
+  *aRetval = true;
+  return NS_OK;
+}
+
+void SessionStorageManager::ClearStorages(
+    const OriginAttributesPattern& aPattern, const nsACString& aOriginScope) {
+  if (CanLoadData()) {
+    nsresult rv = EnsureManager();
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return;
+    }
+
+    mActor->SendClearStorages(aPattern, nsCString(aOriginScope));
+  }
+
+  ClearStoragesInternal(aPattern, aOriginScope);
+}
+
+nsresult SessionStorageManager::Observe(
+    const char* aTopic, const nsAString& aOriginAttributesPattern,
+    const nsACString& aOriginScope) {
+  OriginAttributesPattern pattern;
+  if (!pattern.Init(aOriginAttributesPattern)) {
+    NS_ERROR("Cannot parse origin attributes pattern");
+    return NS_ERROR_FAILURE;
+  }
+
+  // Clear everything, caches + database
+  if (!strcmp(aTopic, "cookie-cleared")) {
+    ClearStorages(pattern, ""_ns);
+    return NS_OK;
+  }
+
+  // Clear from caches everything that has been stored
+  // while in session-only mode
+  if (!strcmp(aTopic, "session-only-cleared")) {
+    ClearStorages(pattern, aOriginScope);
+    return NS_OK;
+  }
+
+  // Clear everything (including so and pb data) from caches and database
+  // for the given domain and subdomains.
+  if (!strcmp(aTopic, "browser:purge-sessionStorage")) {
+    ClearStorages(pattern, aOriginScope);
+    return NS_OK;
+  }
+
+  // Clear entries which match an OriginAttributesPattern.
+  if (!strcmp(aTopic, "dom-storage:clear-origin-attributes-data") ||
+      !strcmp(aTopic, "session-storage:clear-origin-attributes-data")) {
+    ClearStorages(pattern, aOriginScope);
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "profile-change")) {
+    // For case caches are still referenced - clear them completely
+    ClearStorages(pattern, ""_ns);
+    mOATable.Clear();
+    return NS_OK;
+  }
+
+  return NS_OK;
+}
+
+SessionStorageManager::OriginRecord::~OriginRecord() = default;
+
+// static
+void BackgroundSessionStorageManager::RemoveManager(uint64_t aTopContextId) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  AssertIsOnMainThread();
+
+  ::mozilla::ipc::PBackgroundChild* backgroundActor =
+      ::mozilla::ipc::BackgroundChild::GetOrCreateForCurrentThread();
+  if (NS_WARN_IF(!backgroundActor)) {
+    return;
+  }
+
+  if (NS_WARN_IF(!backgroundActor->SendRemoveBackgroundSessionStorageManager(
+          aTopContextId))) {
+    return;
+  }
+}
+
+// static
+void BackgroundSessionStorageManager::PropagateManager(
+    uint64_t aCurrentTopContextId, uint64_t aTargetTopContextId) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  AssertIsOnMainThread();
+  MOZ_ASSERT(aCurrentTopContextId != aTargetTopContextId);
+
+  ::mozilla::ipc::PBackgroundChild* backgroundActor =
+      ::mozilla::ipc::BackgroundChild::GetOrCreateForCurrentThread();
+  if (NS_WARN_IF(!backgroundActor)) {
+    return;
+  }
+
+  if (NS_WARN_IF(!backgroundActor->SendPropagateBackgroundSessionStorageManager(
+          aCurrentTopContextId, aTargetTopContextId))) {
+    return;
+  }
+}
+
+// static
+void BackgroundSessionStorageManager::LoadData(
+    uint64_t aTopContextId,
+    const nsTArray<mozilla::dom::SSCacheCopy>& aCacheCopyList) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  AssertIsOnMainThread();
+
+  ::mozilla::ipc::PBackgroundChild* backgroundActor =
+      ::mozilla::ipc::BackgroundChild::GetOrCreateForCurrentThread();
+  if (NS_WARN_IF(!backgroundActor)) {
+    return;
+  }
+
+  if (NS_WARN_IF(!backgroundActor->SendLoadSessionStorageManagerData(
+          aTopContextId, aCacheCopyList))) {
+    return;
+  }
+}
+
+// static
+BackgroundSessionStorageManager* BackgroundSessionStorageManager::GetOrCreate(
+    uint64_t aTopContextId) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  if (!sManagers) {
+    sManagers = new nsRefPtrHashtable<nsUint64HashKey,
+                                      BackgroundSessionStorageManager>();
+    NS_DispatchToMainThread(NS_NewRunnableFunction(
+        "dom::BackgroundSessionStorageManager::GetOrCreate", [] {
+          RunOnShutdown(
+              [] {
+                ::mozilla::ipc::PBackgroundChild* backgroundActor = ::mozilla::
+                    ipc::BackgroundChild::GetOrCreateForCurrentThread();
+                if (NS_WARN_IF(!backgroundActor)) {
+                  return;
+                }
+
+                if (NS_WARN_IF(
+                        !backgroundActor
+                             ->SendShutdownBackgroundSessionStorageManagers())) {
+                  return;
+                }
+              },
+              ShutdownPhase::XPCOMShutdown);
+        }));
+  }
+
+  return sManagers
+      ->LookupOrInsertWith(
+          aTopContextId,
+          [aTopContextId] {
+            return new BackgroundSessionStorageManager(aTopContextId);
+          })
+      .get();
+}
+
+BackgroundSessionStorageManager::BackgroundSessionStorageManager(
+    uint64_t aBrowsingContextId)
+    : mCurrentBrowsingContextId(aBrowsingContextId) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+}
+
+BackgroundSessionStorageManager::~BackgroundSessionStorageManager() = default;
+
+void BackgroundSessionStorageManager::CopyDataToContentProcess(
+    const nsACString& aOriginAttrs, const nsACString& aOriginKey,
+    nsTArray<SSSetItemInfo>& aData) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  auto* const originRecord =
+      GetOriginRecord(aOriginAttrs, aOriginKey, false, nullptr);
+  if (!originRecord) {
+    return;
+  }
+
+  aData = originRecord->mCache->SerializeData();
+}
+
+/* static */
+RefPtr<BackgroundSessionStorageManager::DataPromise>
+BackgroundSessionStorageManager::GetData(BrowsingContext* aContext,
+                                         uint32_t aSizeLimit,
+                                         bool aClearSessionStoreTimer) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  MOZ_ASSERT(aContext->IsTop());
+
+  AssertIsOnMainThread();
+
+  ::mozilla::ipc::PBackgroundChild* backgroundActor =
+      ::mozilla::ipc::BackgroundChild::GetOrCreateForCurrentThread();
+  if (NS_WARN_IF(!backgroundActor)) {
+    return DataPromise::CreateAndReject(
+        ::mozilla::ipc::ResponseRejectReason::SendError, __func__);
+  }
+
+  return backgroundActor->SendGetSessionStorageManagerData(
+      aContext->Id(), aSizeLimit, aClearSessionStoreTimer);
+}
+
+void BackgroundSessionStorageManager::GetData(
+    uint32_t aSizeLimit, nsTArray<SSCacheCopy>& aCacheCopyList) {
+  for (auto& managerActor : mParticipatingActors) {
+    for (auto* cacheActor :
+         managerActor->ManagedPBackgroundSessionStorageCacheParent()) {
+      auto* cache = static_cast<SessionStorageCacheParent*>(cacheActor);
+      ::mozilla::ipc::PrincipalInfo info = cache->PrincipalInfo();
+
+      OriginAttributes attributes;
+      StoragePrincipalHelper::GetOriginAttributes(cache->PrincipalInfo(),
+                                                  attributes);
+
+      nsAutoCString originAttrs;
+      attributes.CreateSuffix(originAttrs);
+
+      auto* record =
+          GetOriginRecord(originAttrs, cache->OriginKey(), false, nullptr);
+
+      if (!record) {
+        continue;
+      }
+
+      if (record->mCache->GetOriginQuotaUsage() > aSizeLimit) {
+        continue;
+      }
+
+      nsTArray<SSSetItemInfo> data = record->mCache->SerializeData();
+      if (data.IsEmpty()) {
+        continue;
+      }
+
+      SSCacheCopy& cacheCopy = *aCacheCopyList.AppendElement();
+      cacheCopy.originKey() = cache->OriginKey();
+      cacheCopy.principalInfo() = info;
+      cacheCopy.data().SwapElements(data);
+    }
+  }
+}
+
+void BackgroundSessionStorageManager::UpdateData(
+    const nsACString& aOriginAttrs, const nsACString& aOriginKey,
+    const nsTArray<SSWriteInfo>& aWriteInfos) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  auto* const originRecord =
+      GetOriginRecord(aOriginAttrs, aOriginKey, true, nullptr);
+  MOZ_ASSERT(originRecord);
+
+  MaybeScheduleSessionStoreUpdate();
+
+  originRecord->mCache->DeserializeWriteInfos(aWriteInfos);
+}
+
+void BackgroundSessionStorageManager::UpdateData(
+    const nsACString& aOriginAttrs, const nsACString& aOriginKey,
+    const nsTArray<SSSetItemInfo>& aData) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  auto* const originRecord =
+      GetOriginRecord(aOriginAttrs, aOriginKey, true, nullptr);
+  MOZ_ASSERT(originRecord);
+
+  originRecord->mCache->DeserializeData(aData);
+}
+
+void BackgroundSessionStorageManager::ClearStorages(
+    const OriginAttributesPattern& aPattern, const nsACString& aOriginScope) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  ClearStoragesInternal(aPattern, aOriginScope);
+}
+
+void BackgroundSessionStorageManager::ClearStoragesForOrigin(
+    const nsACString& aOriginAttrs, const nsACString& aOriginKey) {
+  ::mozilla::ipc::AssertIsInMainProcess();
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  for (auto& managerActor : mParticipatingActors) {
+    QM_WARNONLY_TRY(OkIf(managerActor->SendClearStoragesForOrigin(
+        nsCString(aOriginAttrs), nsCString(aOriginKey))));
+  }
+
+  ClearStoragesForOriginInternal(aOriginAttrs, aOriginKey);
+}
+
+void BackgroundSessionStorageManager::SetCurrentBrowsingContextId(
+    uint64_t aBrowsingContextId) {
+  MOZ_DIAGNOSTIC_ASSERT(aBrowsingContextId != mCurrentBrowsingContextId);
+  mCurrentBrowsingContextId = aBrowsingContextId;
+}
+
+void BackgroundSessionStorageManager::MaybeScheduleSessionStoreUpdate() {
+  if (!StaticPrefs::browser_sessionstore_platform_collection_AtStartup()) {
+    return;
+  }
+
+  if (mSessionStoreCallbackTimer) {
+    return;
+  }
+
+  if (StaticPrefs::browser_sessionstore_debug_no_auto_updates()) {
+    DispatchSessionStoreUpdate();
+    return;
+  }
+
+  auto result = NS_NewTimerWithFuncCallback(
+      [](nsITimer*, void* aClosure) {
+        auto* mgr = static_cast<BackgroundSessionStorageManager*>(aClosure);
+        mgr->DispatchSessionStoreUpdate();
+      },
+      this, StaticPrefs::browser_sessionstore_interval(),
+      nsITimer::TYPE_ONE_SHOT,
+      "BackgroundSessionStorageManager::DispatchSessionStoreUpdate");
+
+  if (result.isErr()) {
+    return;
+  }
+
+  mSessionStoreCallbackTimer = result.unwrap();
+}
+
+void BackgroundSessionStorageManager::MaybeDispatchSessionStoreUpdate() {
+  if (mSessionStoreCallbackTimer) {
+    BackgroundSessionStorageManager::DispatchSessionStoreUpdate();
+  }
+}
+
+void BackgroundSessionStorageManager::DispatchSessionStoreUpdate() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  NS_DispatchToMainThread(NS_NewRunnableFunction(
+      "CanonicalBrowsingContext::UpdateSessionStore",
+      [targetBrowsingContextId = mCurrentBrowsingContextId]() {
+        CanonicalBrowsingContext::UpdateSessionStoreForStorage(
+            targetBrowsingContextId);
+      }));
+
+  CancelSessionStoreUpdate();
+}
+
+void BackgroundSessionStorageManager::CancelSessionStoreUpdate() {
+  if (mSessionStoreCallbackTimer) {
+    mSessionStoreCallbackTimer->Cancel();
+    mSessionStoreCallbackTimer = nullptr;
+  }
+}
+
+void BackgroundSessionStorageManager::AddParticipatingActor(
+    SessionStorageManagerParent* aActor) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  mParticipatingActors.AppendElement(aActor);
+}
+
+void BackgroundSessionStorageManager::RemoveParticipatingActor(
+    SessionStorageManagerParent* aActor) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  mParticipatingActors.RemoveElement(aActor);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/storage/SessionStorageManager.h b/dom/storage/SessionStorageManager.h
new file mode 100644
index 0000000000..4880f13270
--- /dev/null
+++ b/dom/storage/SessionStorageManager.h
@@ -0,0 +1,285 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_dom_SessionStorageManager_h
+#define mozilla_dom_SessionStorageManager_h
+
+#include "StorageObserver.h"
+
+#include "mozilla/dom/FlippedOnce.h"
+#include "nsIDOMStorageManager.h"
+#include "nsClassHashtable.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsHashKeys.h"
+
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/ipc/PBackgroundParent.h"
+
+class nsIPrincipal;
+class nsITimer;
+
+namespace mozilla {
+class OriginAttributesPattern;
+
+namespace dom {
+
+class SSCacheCopy;
+
+bool RecvShutdownBackgroundSessionStorageManagers();
+void RecvPropagateBackgroundSessionStorageManager(uint64_t aCurrentTopContextId,
+                                                  uint64_t aTargetTopContextId);
+bool RecvRemoveBackgroundSessionStorageManager(uint64_t aTopContextId);
+
+bool RecvGetSessionStorageData(
+    uint64_t aTopContextId, uint32_t aSizeLimit, bool aCancelSessionStoreTimer,
+    ::mozilla::ipc::PBackgroundParent::GetSessionStorageManagerDataResolver&&
+        aResolver);
+
+bool RecvLoadSessionStorageData(
+    uint64_t aTopContextId,
+    nsTArray<mozilla::dom::SSCacheCopy>&& aCacheCopyList);
+
+bool RecvClearStoragesForOrigin(const nsACString& aOriginAttrs,
+                                const nsACString& aOriginKey);
+
+class BrowsingContext;
+class ContentParent;
+class SSSetItemInfo;
+class SSWriteInfo;
+class SessionStorageCache;
+class SessionStorageCacheChild;
+class SessionStorageManagerChild;
+class SessionStorageManagerParent;
+class SessionStorageObserver;
+struct OriginRecord;
+
+// sessionStorage is a data store that's unique to each tab (i.e. top-level
+// browsing context) and origin. Before the advent of Fission all the data
+// for a given tab could be stored in a single content process; now each
+// site-specific process stores only its portion of the data. As content
+// processes terminate, their sessionStorage data needs to be saved in the
+// parent process, in case the same origin appears again in the tab (e.g.
+// by navigating an iframe element). Therefore SessionStorageManager
+// objects exist in both the parent and content processes.
+//
+// Whenever a write operation for SessionStorage executes, the content process
+// sends the changes to the parent process at the next stable state. Whenever a
+// content process navigates to an origin for the first time in a given tab, the
+// parent process sends it the saved data. SessionStorageCache has a flag
+// (mLoadedOrCloned) to ensure that it's only be loaded or cloned once.
+//
+// Note: the current implementation is expected to be replaced by a new
+// implementation using LSNG.
+class SessionStorageManagerBase {
+ public:
+  SessionStorageManagerBase() = default;
+
+ protected:
+  ~SessionStorageManagerBase() = default;
+
+  struct OriginRecord {
+    OriginRecord() = default;
+    OriginRecord(OriginRecord&&) = default;
+    OriginRecord& operator=(OriginRecord&&) = default;
+    ~OriginRecord();
+
+    RefPtr<SessionStorageCache> mCache;
+
+    // A flag to ensure that cache is only loaded once.
+    FlippedOnce<false> mLoaded;
+  };
+
+  void ClearStoragesInternal(const OriginAttributesPattern& aPattern,
+                             const nsACString& aOriginScope);
+
+  void ClearStoragesForOriginInternal(const nsACString& aOriginAttrs,
+                                      const nsACString& aOriginKey);
+
+  OriginRecord* GetOriginRecord(const nsACString& aOriginAttrs,
+                                const nsACString& aOriginKey,
+                                bool aMakeIfNeeded,
+                                SessionStorageCache* aCloneFrom);
+
+  using OriginKeyHashTable = nsClassHashtable<nsCStringHashKey, OriginRecord>;
+  nsClassHashtable<nsCStringHashKey, OriginKeyHashTable> mOATable;
+};
+
+class SessionStorageManager final : public SessionStorageManagerBase,
+                                    public nsIDOMSessionStorageManager,
+                                    public StorageObserverSink {
+ public:
+  explicit SessionStorageManager(RefPtr<BrowsingContext> aBrowsingContext);
+
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_NSIDOMSTORAGEMANAGER
+  NS_DECL_NSIDOMSESSIONSTORAGEMANAGER
+
+  NS_DECL_CYCLE_COLLECTION_CLASS(SessionStorageManager)
+
+  bool CanLoadData();
+
+  void SetActor(SessionStorageManagerChild* aActor);
+
+  bool ActorExists() const;
+
+  void ClearActor();
+
+  nsresult EnsureManager();
+
+  nsresult LoadData(nsIPrincipal& aPrincipal, SessionStorageCache& aCache);
+
+  void CheckpointData(nsIPrincipal& aPrincipal, SessionStorageCache& aCache);
+
+  nsresult ClearStoragesForOrigin(const nsACString& aOriginAttrs,
+                                  const nsACString& aOriginKey);
+
+ private:
+  ~SessionStorageManager();
+
+  // StorageObserverSink, handler to various chrome clearing notification
+  nsresult Observe(const char* aTopic,
+                   const nsAString& aOriginAttributesPattern,
+                   const nsACString& aOriginScope) override;
+
+  nsresult GetSessionStorageCacheHelper(nsIPrincipal* aPrincipal,
+                                        bool aMakeIfNeeded,
+                                        SessionStorageCache* aCloneFrom,
+                                        RefPtr<SessionStorageCache>* aRetVal);
+
+  nsresult GetSessionStorageCacheHelper(const nsACString& aOriginAttrs,
+                                        const nsACString& aOriginKey,
+                                        bool aMakeIfNeeded,
+                                        SessionStorageCache* aCloneFrom,
+                                        RefPtr<SessionStorageCache>* aRetVal);
+
+  void ClearStorages(const OriginAttributesPattern& aPattern,
+                     const nsACString& aOriginScope);
+
+  SessionStorageCacheChild* EnsureCache(nsIPrincipal& aPrincipal,
+                                        const nsACString& aOriginKey,
+                                        SessionStorageCache& aCache);
+
+  void CheckpointDataInternal(nsIPrincipal& aPrincipal,
+                              const nsACString& aOriginKey,
+                              SessionStorageCache& aCache);
+
+  RefPtr<SessionStorageObserver> mObserver;
+
+  RefPtr<BrowsingContext> mBrowsingContext;
+
+  SessionStorageManagerChild* mActor;
+};
+
+/**
+ * A specialized SessionStorageManager class that lives on the parent process
+ * background thread. It is a shadow copy of SessionStorageManager and it's used
+ * to preserve SessionStorageCaches for the other SessionStorageManagers.
+ */
+class BackgroundSessionStorageManager final : public SessionStorageManagerBase {
+ public:
+  // Parent process getter function.
+  static BackgroundSessionStorageManager* GetOrCreate(uint64_t aTopContextId);
+
+  NS_INLINE_DECL_REFCOUNTING(BackgroundSessionStorageManager);
+
+  // Only called by CanonicalBrowsingContext::ReplaceBy on the parent process.
+  static void PropagateManager(uint64_t aCurrentTopContextId,
+                               uint64_t aTargetTopContextId);
+
+  // Only called by CanonicalBrowsingContext::CanonicalDiscard on parent
+  // process.
+  static void RemoveManager(uint64_t aTopContextId);
+
+  static void LoadData(
+      uint64_t aTopContextId,
+      const nsTArray<mozilla::dom::SSCacheCopy>& aCacheCopyList);
+
+  using DataPromise =
+      ::mozilla::ipc::PBackgroundChild::GetSessionStorageManagerDataPromise;
+  static RefPtr<DataPromise> GetData(BrowsingContext* aContext,
+                                     uint32_t aSizeLimit,
+                                     bool aClearSessionStoreTimer = false);
+
+  void GetData(uint32_t aSizeLimit, nsTArray<SSCacheCopy>& aCacheCopyList);
+
+  void CopyDataToContentProcess(const nsACString& aOriginAttrs,
+                                const nsACString& aOriginKey,
+                                nsTArray<SSSetItemInfo>& aData);
+
+  void UpdateData(const nsACString& aOriginAttrs, const nsACString& aOriginKey,
+                  const nsTArray<SSWriteInfo>& aWriteInfos);
+
+  void UpdateData(const nsACString& aOriginAttrs, const nsACString& aOriginKey,
+                  const nsTArray<SSSetItemInfo>& aData);
+
+  void ClearStorages(const OriginAttributesPattern& aPattern,
+                     const nsACString& aOriginScope);
+
+  void ClearStoragesForOrigin(const nsACString& aOriginAttrs,
+                              const nsACString& aOriginKey);
+
+  void SetCurrentBrowsingContextId(uint64_t aBrowsingContextId);
+
+  void MaybeDispatchSessionStoreUpdate();
+
+  void CancelSessionStoreUpdate();
+
+  void AddParticipatingActor(SessionStorageManagerParent* aActor);
+
+  void RemoveParticipatingActor(SessionStorageManagerParent* aActor);
+
+ private:
+  // Only be called by GetOrCreate() on the parent process.
+  explicit BackgroundSessionStorageManager(uint64_t aBrowsingContextId);
+
+  ~BackgroundSessionStorageManager();
+
+  // Sets a timer for notifying main thread that the cache has been
+  // updated. May do nothing if we're coalescing notifications.
+  void MaybeScheduleSessionStoreUpdate();
+
+  void DispatchSessionStoreUpdate();
+
+  // The most current browsing context using this manager
+  uint64_t mCurrentBrowsingContextId;
+
+  // Callback for notifying main thread of calls to `UpdateData`.
+  //
+  // A timer that is held whenever this manager has dirty state that
+  // has not yet been reflected to the main thread. The timer is used
+  // to delay notifying the main thread to ask for changes, thereby
+  // coalescing/throttling changes. (Note that SessionStorage, like
+  // LocalStorage, treats attempts to set a value to its current value
+  // as a no-op.)
+  //
+
+  // The timer is initialized with a fixed delay as soon as the state
+  // becomes dirty; additional mutations to our state will not reset
+  // the timer because then we might never flush to the main
+  // thread. The timer is cleared only when a new set of data is sent
+  // to the main thread and therefore this manager no longer has any
+  // dirty state. This means that there is a period of time after the
+  // nsITimer fires where this value is non-null but there is no
+  // scheduled timer while we wait for the main thread to request the
+  // new state. Callers of GetData can also optionally cancel the
+  // current timer to reduce the amounts of notifications.
+  //
+  // When this manager is moved to a new top-level browsing context id
+  // via a PropagateBackgroundSessionStorageManager message, the
+  // behavior of the timer doesn't change because the main thread knows
+  // about the renaming and is initiating it (and any in-flight
+  // GetSessionStorageManagerData requests will be unaffected because
+  // they use async-returns so the response is inherently matched up via
+  // the issued promise).
+  nsCOMPtr<nsITimer> mSessionStoreCallbackTimer;
+
+  nsTArray<RefPtr<SessionStorageManagerParent>> mParticipatingActors;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_SessionStorageManager_h
diff --git a/dom/storage/SessionStorageObserver.cpp b/dom/storage/SessionStorageObserver.cpp
new file mode 100644
index 0000000000..2963a046be
--- /dev/null
+++ b/dom/storage/SessionStorageObserver.cpp
@@ -0,0 +1,55 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 et sw=2 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/. */
+
+#include "SessionStorageObserver.h"
+#include "StorageIPC.h"
+#include "mozilla/dom/LocalStorageCommon.h"
+
+namespace mozilla::dom {
+
+namespace {
+
+SessionStorageObserver* gSessionStorageObserver = nullptr;
+
+}  // namespace
+
+SessionStorageObserver::SessionStorageObserver() : mActor(nullptr) {
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(NextGenLocalStorageEnabled());
+
+  MOZ_ASSERT(!gSessionStorageObserver);
+  gSessionStorageObserver = this;
+}
+
+SessionStorageObserver::~SessionStorageObserver() {
+  AssertIsOnOwningThread();
+
+  if (mActor) {
+    mActor->SendDeleteMeInternal();
+    MOZ_ASSERT(!mActor, "SendDeleteMeInternal should have cleared!");
+  }
+
+  MOZ_ASSERT(gSessionStorageObserver);
+  gSessionStorageObserver = nullptr;
+}
+
+// static
+SessionStorageObserver* SessionStorageObserver::Get() {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(NextGenLocalStorageEnabled());
+
+  return gSessionStorageObserver;
+}
+
+void SessionStorageObserver::SetActor(SessionStorageObserverChild* aActor) {
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aActor);
+  MOZ_ASSERT(!mActor);
+
+  mActor = aActor;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/storage/SessionStorageObserver.h b/dom/storage/SessionStorageObserver.h
new file mode 100644
index 0000000000..dee472cc9c
--- /dev/null
+++ b/dom/storage/SessionStorageObserver.h
@@ -0,0 +1,63 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_dom_SessionStorageObserver_h
+#define mozilla_dom_SessionStorageObserver_h
+
+#include "nsISupportsImpl.h"
+
+namespace mozilla::dom {
+
+class SessionStorageObserverChild;
+
+/**
+ * Effectively just a refcounted life-cycle management wrapper around
+ * SessionStorageObserverChild which exists to receive chrome observer
+ * notifications from the main process.
+ *
+ * ## Lifecycle ##
+ * - Created by SessionStorageManager::SessionStorageManager.  Placed in the
+ *   gSessionStorageObserver variable for subsequent SessionStorageManager's via
+ *   SessionStorageObserver::Get lookup.
+ * - The SessionStorageObserverChild directly handles "Observe" messages,
+ *   shunting them directly to StorageObserver::Notify which distributes them to
+ *   individual observer sinks.
+ * - Destroyed when refcount goes to zero due to all owning
+ *   SessionStorageManager being destroyed.
+ */
+class SessionStorageObserver final {
+  friend class SessionStorageManager;
+
+  SessionStorageObserverChild* mActor;
+
+ public:
+  static SessionStorageObserver* Get();
+
+  NS_INLINE_DECL_REFCOUNTING(SessionStorageObserver)
+
+  void AssertIsOnOwningThread() const {
+    NS_ASSERT_OWNINGTHREAD(SessionStorageObserver);
+  }
+
+  void SetActor(SessionStorageObserverChild* aActor);
+
+  void ClearActor() {
+    AssertIsOnOwningThread();
+    MOZ_ASSERT(mActor);
+
+    mActor = nullptr;
+  }
+
+ private:
+  // Only created by SessionStorageManager.
+  SessionStorageObserver();
+
+  ~SessionStorageObserver();
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_SessionStorageObserver_h
diff --git a/dom/storage/SessionStorageService.cpp b/dom/storage/SessionStorageService.cpp
new file mode 100644
index 0000000000..fe42354c09
--- /dev/null
+++ b/dom/storage/SessionStorageService.cpp
@@ -0,0 +1,134 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "SessionStorageService.h"
+
+#include "MainThreadUtils.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/Components.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+
+namespace mozilla::dom {
+
+using namespace mozilla::ipc;
+
+namespace {
+
+StaticRefPtr<SessionStorageService> gSessionStorageService;
+
+bool gShutdown(false);
+
+}  // namespace
+
+NS_IMPL_ISUPPORTS(SessionStorageService, nsISessionStorageService)
+
+NS_IMETHODIMP
+SessionStorageService::ClearStoragesForOrigin(nsIPrincipal* aPrincipal) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(aPrincipal);
+
+  QM_TRY_INSPECT(const auto& originAttrs,
+                 MOZ_TO_RESULT_INVOKE_MEMBER_TYPED(nsCString, aPrincipal,
+                                                   GetOriginSuffix));
+
+  QM_TRY_INSPECT(const auto& originKey,
+                 MOZ_TO_RESULT_INVOKE_MEMBER_TYPED(nsCString, aPrincipal,
+                                                   GetStorageOriginKey));
+
+  QM_TRY(OkIf(SendClearStoragesForOrigin(originAttrs, originKey)),
+         NS_ERROR_FAILURE);
+
+  return NS_OK;
+}
+
+SessionStorageService::SessionStorageService() { AssertIsOnMainThread(); }
+
+SessionStorageService::~SessionStorageService() {
+  AssertIsOnMainThread();
+  MOZ_ASSERT_IF(mInitialized, mActorDestroyed);
+}
+
+// static
+Result<RefPtr<SessionStorageService>, nsresult> SessionStorageService::Acquire(
+    const CreateIfNonExistent&) {
+  AssertIsOnMainThread();
+
+  QM_TRY(OkIf(!gShutdown), Err(NS_ERROR_ILLEGAL_DURING_SHUTDOWN));
+
+  if (gSessionStorageService) {
+    return RefPtr<SessionStorageService>(gSessionStorageService);
+  }
+
+  auto sessionStorageService = MakeRefPtr<SessionStorageService>();
+
+  QM_TRY(sessionStorageService->Init());
+
+  gSessionStorageService = sessionStorageService;
+
+  RunOnShutdown(
+      [] {
+        gShutdown = true;
+
+        gSessionStorageService->Shutdown();
+
+        gSessionStorageService = nullptr;
+      },
+      ShutdownPhase::XPCOMShutdown);
+
+  return sessionStorageService;
+}
+
+// static
+RefPtr<SessionStorageService> SessionStorageService::Acquire() {
+  AssertIsOnMainThread();
+
+  return gSessionStorageService;
+}
+
+Result<Ok, nsresult> SessionStorageService::Init() {
+  AssertIsOnMainThread();
+
+  PBackgroundChild* backgroundActor =
+      BackgroundChild::GetOrCreateForCurrentThread();
+  QM_TRY(OkIf(backgroundActor), Err(NS_ERROR_FAILURE));
+
+  QM_TRY(OkIf(backgroundActor->SendPBackgroundSessionStorageServiceConstructor(
+             this)),
+         Err(NS_ERROR_FAILURE));
+
+  mInitialized.Flip();
+
+  return Ok{};
+}
+
+void SessionStorageService::Shutdown() {
+  AssertIsOnMainThread();
+
+  if (!mActorDestroyed) {
+    QM_WARNONLY_TRY(OkIf(Send__delete__(this)));
+  }
+}
+
+void SessionStorageService::ActorDestroy(ActorDestroyReason /* aWhy */) {
+  AssertIsOnMainThread();
+
+  mActorDestroyed.Flip();
+}
+
+}  // namespace mozilla::dom
+
+NS_IMPL_COMPONENT_FACTORY(nsISessionStorageService) {
+  mozilla::AssertIsOnMainThread();
+
+  QM_TRY_UNWRAP(auto sessionStorageService,
+                mozilla::dom::SessionStorageService::Acquire(
+                    mozilla::CreateIfNonExistent{}),
+                nullptr);
+
+  return sessionStorageService.forget().downcast<nsISupports>();
+}
diff --git a/dom/storage/SessionStorageService.h b/dom/storage/SessionStorageService.h
new file mode 100644
index 0000000000..70b780a0ee
--- /dev/null
+++ b/dom/storage/SessionStorageService.h
@@ -0,0 +1,55 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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 DOM_STORAGE_SESSIONSTORAGESERVICE_H_
+#define DOM_STORAGE_SESSIONSTORAGESERVICE_H_
+
+#include "nsISessionStorageService.h"
+#include "mozilla/Result.h"
+#include "mozilla/dom/FlippedOnce.h"
+#include "mozilla/dom/PBackgroundSessionStorageServiceChild.h"
+
+namespace mozilla {
+
+struct CreateIfNonExistent;
+
+namespace dom {
+
+class SessionStorageService final
+    : public nsISessionStorageService,
+      public PBackgroundSessionStorageServiceChild {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSISESSIONSTORAGESERVICE
+
+  SessionStorageService();
+
+  // Singleton Boilerplate
+  static mozilla::Result<RefPtr<SessionStorageService>, nsresult> Acquire(
+      const CreateIfNonExistent&);
+
+  // Can return null if the service hasn't be created yet or after
+  // XPCOMShutdown.
+  static RefPtr<SessionStorageService> Acquire();
+
+ private:
+  ~SessionStorageService();
+
+  mozilla::Result<Ok, nsresult> Init();
+
+  void Shutdown();
+
+  // IPDL methods are only called by IPDL.
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  FlippedOnce<false> mInitialized;
+  FlippedOnce<false> mActorDestroyed;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif /* DOM_STORAGE_SESSIONSTORAGESERVICE_H_ */
diff --git a/dom/storage/Storage.cpp b/dom/storage/Storage.cpp
new file mode 100644
index 0000000000..cf0f4f32d7
--- /dev/null
+++ b/dom/storage/Storage.cpp
@@ -0,0 +1,156 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "Storage.h"
+#include "StorageNotifierService.h"
+
+#include "mozilla/dom/StorageBinding.h"
+#include "mozilla/dom/StorageEvent.h"
+#include "mozilla/dom/StorageEventBinding.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/SchedulerGroup.h"
+#include "mozilla/Services.h"
+#include "mozilla/StaticPrefs_dom.h"
+#include "mozilla/StorageAccess.h"
+#include "nsIObserverService.h"
+#include "nsPIDOMWindow.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(Storage, mWindow, mPrincipal,
+                                      mStoragePrincipal)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(Storage)
+NS_IMPL_CYCLE_COLLECTING_RELEASE_WITH_LAST_RELEASE(Storage, LastRelease())
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(Storage)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+Storage::Storage(nsPIDOMWindowInner* aWindow, nsIPrincipal* aPrincipal,
+                 nsIPrincipal* aStoragePrincipal)
+    : mWindow(aWindow),
+      mPrincipal(aPrincipal),
+      mStoragePrincipal(aStoragePrincipal),
+      mPrivateBrowsing(false),
+      mSessionScopedOrLess(false) {
+  MOZ_ASSERT(aPrincipal);
+
+  if (mPrincipal->IsSystemPrincipal()) {
+    mPrivateBrowsing = false;
+    mSessionScopedOrLess = false;
+  } else if (mWindow) {
+    uint32_t rejectedReason = 0;
+    StorageAccess access = StorageAllowedForWindow(mWindow, &rejectedReason);
+
+    mPrivateBrowsing = access == StorageAccess::ePrivateBrowsing;
+    mSessionScopedOrLess = access <= StorageAccess::eSessionScoped;
+  }
+}
+
+Storage::~Storage() = default;
+
+/* static */
+bool Storage::StoragePrefIsEnabled() {
+  return StaticPrefs::dom_storage_enabled();
+}
+
+int64_t Storage::GetSnapshotUsage(nsIPrincipal& aSubjectPrincipal,
+                                  ErrorResult& aRv) {
+  aRv.Throw(NS_ERROR_NOT_IMPLEMENTED);
+  return 0;
+}
+
+bool Storage::CanUseStorage(nsIPrincipal& aSubjectPrincipal) {
+  if (!StoragePrefIsEnabled()) {
+    return false;
+  }
+
+  return aSubjectPrincipal.Subsumes(mPrincipal);
+}
+
+/* virtual */
+JSObject* Storage::WrapObject(JSContext* aCx,
+                              JS::Handle<JSObject*> aGivenProto) {
+  return Storage_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+namespace {
+
+class StorageNotifierRunnable : public Runnable {
+ public:
+  StorageNotifierRunnable(nsISupports* aSubject, const char16_t* aStorageType,
+                          bool aPrivateBrowsing)
+      : Runnable("StorageNotifierRunnable"),
+        mSubject(aSubject),
+        mStorageType(aStorageType),
+        mPrivateBrowsing(aPrivateBrowsing) {}
+
+  NS_IMETHOD
+  Run() override {
+    nsCOMPtr<nsIObserverService> observerService =
+        mozilla::services::GetObserverService();
+    if (observerService) {
+      observerService->NotifyObservers(mSubject,
+                                       mPrivateBrowsing
+                                           ? "dom-private-storage2-changed"
+                                           : "dom-storage2-changed",
+                                       mStorageType);
+    }
+    return NS_OK;
+  }
+
+ private:
+  nsCOMPtr<nsISupports> mSubject;
+  const char16_t* mStorageType;
+  const bool mPrivateBrowsing;
+};
+
+}  // namespace
+
+/* static */
+void Storage::NotifyChange(Storage* aStorage, nsIPrincipal* aPrincipal,
+                           const nsAString& aKey, const nsAString& aOldValue,
+                           const nsAString& aNewValue,
+                           const char16_t* aStorageType,
+                           const nsAString& aDocumentURI, bool aIsPrivate,
+                           bool aImmediateDispatch) {
+  StorageEventInit dict;
+  dict.mBubbles = false;
+  dict.mCancelable = false;
+  dict.mKey = aKey;
+  dict.mNewValue = aNewValue;
+  dict.mOldValue = aOldValue;
+  dict.mStorageArea = aStorage;
+  dict.mUrl = aDocumentURI;
+
+  // Note, this DOM event should never reach JS. It is cloned later in
+  // nsGlobalWindow.
+  RefPtr<StorageEvent> event =
+      StorageEvent::Constructor(nullptr, u"storage"_ns, dict);
+
+  event->SetPrincipal(aPrincipal);
+
+  // This will send the event to any registered window.
+  StorageNotifierService::Broadcast(event, aStorageType, aIsPrivate,
+                                    aImmediateDispatch);
+
+  // This runnable is mainly used by devtools. Windows receive notification by
+  // StorageNotifierService.
+
+  RefPtr<StorageNotifierRunnable> r =
+      new StorageNotifierRunnable(event, aStorageType, aIsPrivate);
+
+  if (aImmediateDispatch) {
+    Unused << r->Run();
+  } else {
+    SchedulerGroup::Dispatch(TaskCategory::Other, r.forget());
+  }
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/storage/Storage.h b/dom/storage/Storage.h
new file mode 100644
index 0000000000..81546a0b0e
--- /dev/null
+++ b/dom/storage/Storage.h
@@ -0,0 +1,180 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_dom_Storage_h
+#define mozilla_dom_Storage_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/Maybe.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsCOMPtr.h"
+#include "nsWrapperCache.h"
+#include "nsISupports.h"
+#include "nsTArrayForwardDeclare.h"
+#include "nsString.h"
+
+class nsIPrincipal;
+class nsPIDOMWindowInner;
+
+namespace mozilla::dom {
+
+class Storage : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(Storage)
+
+  Storage(nsPIDOMWindowInner* aWindow, nsIPrincipal* aPrincipal,
+          nsIPrincipal* aStoragePrincipal);
+
+  static bool StoragePrefIsEnabled();
+
+  enum StorageType {
+    eSessionStorage,
+    eLocalStorage,
+    ePartitionedLocalStorage,
+  };
+
+  virtual StorageType Type() const = 0;
+
+  virtual bool IsForkOf(const Storage* aStorage) const = 0;
+
+  virtual int64_t GetOriginQuotaUsage() const = 0;
+
+  virtual void Disconnect() {}
+
+  nsIPrincipal* Principal() const { return mPrincipal; }
+
+  nsIPrincipal* StoragePrincipal() const { return mStoragePrincipal; }
+
+  bool IsPrivateBrowsing() const { return mPrivateBrowsing; }
+
+  bool IsSessionScopedOrLess() const { return mSessionScopedOrLess; }
+
+  // WebIDL
+  JSObject* WrapObject(JSContext* aCx,
+                       JS::Handle<JSObject*> aGivenProto) override;
+
+  nsPIDOMWindowInner* GetParentObject() const { return mWindow; }
+
+  virtual uint32_t GetLength(nsIPrincipal& aSubjectPrincipal,
+                             ErrorResult& aRv) = 0;
+
+  virtual void Key(uint32_t aIndex, nsAString& aResult,
+                   nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) = 0;
+
+  virtual void GetItem(const nsAString& aKey, nsAString& aResult,
+                       nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) = 0;
+
+  virtual void GetSupportedNames(nsTArray<nsString>& aKeys) = 0;
+
+  void NamedGetter(const nsAString& aKey, bool& aFound, nsAString& aResult,
+                   nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) {
+    GetItem(aKey, aResult, aSubjectPrincipal, aRv);
+    aFound = !aResult.IsVoid();
+  }
+
+  virtual void SetItem(const nsAString& aKey, const nsAString& aValue,
+                       nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) = 0;
+
+  void NamedSetter(const nsAString& aKey, const nsAString& aValue,
+                   nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) {
+    SetItem(aKey, aValue, aSubjectPrincipal, aRv);
+  }
+
+  virtual void RemoveItem(const nsAString& aKey,
+                          nsIPrincipal& aSubjectPrincipal,
+                          ErrorResult& aRv) = 0;
+
+  void NamedDeleter(const nsAString& aKey, bool& aFound,
+                    nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) {
+    RemoveItem(aKey, aSubjectPrincipal, aRv);
+
+    aFound = !aRv.ErrorCodeIs(NS_SUCCESS_DOM_NO_OPERATION);
+  }
+
+  virtual void Clear(nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) = 0;
+
+  // The attribute in the WebIDL interface has rather confusing name. So we
+  // shouldn't use this method internally. IsSessionScopedOrLess should be used
+  // directly.
+  bool IsSessionOnly() const { return IsSessionScopedOrLess(); }
+
+  //////////////////////////////////////////////////////////////////////////////
+  // Testing Methods:
+  //
+  // These methods are exposed on the `Storage` WebIDL interface behind a
+  // preference for the benefit of automated-tests.  They are not exposed to
+  // content.  See `Storage.webidl` for more details.
+
+  virtual void Open(nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) {}
+
+  virtual void Close(nsIPrincipal& aSubjectPrincipal, ErrorResult& aRv) {}
+
+  virtual void BeginExplicitSnapshot(nsIPrincipal& aSubjectPrincipal,
+                                     ErrorResult& aRv) {}
+
+  virtual void CheckpointExplicitSnapshot(nsIPrincipal& aSubjectPrincipal,
+                                          ErrorResult& aRv) {}
+
+  virtual void EndExplicitSnapshot(nsIPrincipal& aSubjectPrincipal,
+                                   ErrorResult& aRv) {}
+
+  virtual bool GetHasSnapshot(nsIPrincipal& aSubjectPrincipal,
+                              ErrorResult& aRv) {
+    return false;
+  }
+
+  virtual int64_t GetSnapshotUsage(nsIPrincipal& aSubjectPrincipal,
+                                   ErrorResult& aRv);
+
+  //////////////////////////////////////////////////////////////////////////////
+
+  // Dispatch storage notification events on all impacted pages in the current
+  // process as well as for consumption by devtools.  Pages receive the
+  // notification via StorageNotifierService (not observers like in the past),
+  // while devtools does receive the notification via the observer service.
+  //
+  // aStorage can be null if this method is called by LocalStorageCacheChild.
+  //
+  // aImmediateDispatch is for use by child IPC code (LocalStorageCacheChild)
+  // so that PBackground ordering can be maintained.  Without this, the event
+  // would be enqueued and run in a future turn of the event loop, potentially
+  // allowing other PBackground Recv* methods to trigger script that wants to
+  // assume our localstorage changes have already been applied.  This is the
+  // case for message manager messages which are used by ContentTask testing
+  // logic and webextensions.
+  static void NotifyChange(Storage* aStorage, nsIPrincipal* aPrincipal,
+                           const nsAString& aKey, const nsAString& aOldValue,
+                           const nsAString& aNewValue,
+                           const char16_t* aStorageType,
+                           const nsAString& aDocumentURI, bool aIsPrivate,
+                           bool aImmediateDispatch);
+
+ protected:
+  virtual ~Storage();
+
+  // The method checks whether the caller can use a storage.
+  bool CanUseStorage(nsIPrincipal& aSubjectPrincipal);
+
+  virtual void LastRelease() {}
+
+ private:
+  nsCOMPtr<nsPIDOMWindowInner> mWindow;
+  nsCOMPtr<nsIPrincipal> mPrincipal;
+  nsCOMPtr<nsIPrincipal> mStoragePrincipal;
+
+  bool mPrivateBrowsing : 1;
+
+  // Whether storage is set to persist data only per session, may change
+  // dynamically and is set by CanUseStorage function that is called
+  // before any operation on the storage.
+  bool mSessionScopedOrLess : 1;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_Storage_h
diff --git a/dom/storage/StorageActivityService.cpp b/dom/storage/StorageActivityService.cpp
new file mode 100644
index 0000000000..8652d82653
--- /dev/null
+++ b/dom/storage/StorageActivityService.cpp
@@ -0,0 +1,302 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "StorageActivityService.h"
+
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/ipc/BackgroundUtils.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/ipc/PBackgroundSharedTypes.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/SchedulerGroup.h"
+#include "mozilla/Services.h"
+#include "mozilla/StaticPtr.h"
+#include "nsCOMPtr.h"
+#include "nsComponentManagerUtils.h"
+#include "nsIMutableArray.h"
+#include "nsIObserverService.h"
+#include "nsIPrincipal.h"
+#include "nsIUserIdleService.h"
+#include "nsSupportsPrimitives.h"
+#include "nsXPCOM.h"
+
+// This const is used to know when origin activities should be purged because
+// too old. This value should be in sync with what the UI needs.
+#define TIME_MAX_SECS 86400 /* 24 hours */
+
+namespace mozilla::dom {
+
+static StaticRefPtr<StorageActivityService> gStorageActivityService;
+static bool gStorageActivityShutdown = false;
+
+/* static */
+void StorageActivityService::SendActivity(nsIPrincipal* aPrincipal) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (!aPrincipal || BasePrincipal::Cast(aPrincipal)->Kind() !=
+                         BasePrincipal::eContentPrincipal) {
+    // Only content principals.
+    return;
+  }
+
+  RefPtr<StorageActivityService> service = GetOrCreate();
+  if (NS_WARN_IF(!service)) {
+    return;
+  }
+
+  service->SendActivityInternal(aPrincipal);
+}
+
+/* static */
+void StorageActivityService::SendActivity(
+    const mozilla::ipc::PrincipalInfo& aPrincipalInfo) {
+  if (aPrincipalInfo.type() !=
+      mozilla::ipc::PrincipalInfo::TContentPrincipalInfo) {
+    // only content principal.
+    return;
+  }
+
+  RefPtr<Runnable> r = NS_NewRunnableFunction(
+      "StorageActivityService::SendActivity", [aPrincipalInfo]() {
+        MOZ_ASSERT(NS_IsMainThread());
+
+        auto principalOrErr =
+            mozilla::ipc::PrincipalInfoToPrincipal(aPrincipalInfo);
+
+        if (principalOrErr.isOk()) {
+          nsCOMPtr<nsIPrincipal> principal = principalOrErr.unwrap();
+          StorageActivityService::SendActivity(principal);
+        } else {
+          NS_WARNING(
+              "Could not obtain principal from "
+              "mozilla::ipc::PrincipalInfoToPrincipal");
+        }
+      });
+
+  SchedulerGroup::Dispatch(TaskCategory::Other, r.forget());
+}
+
+/* static */
+void StorageActivityService::SendActivity(const nsACString& aOrigin) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  nsCString origin;
+  origin.Assign(aOrigin);
+
+  RefPtr<Runnable> r = NS_NewRunnableFunction(
+      "StorageActivityService::SendActivity", [origin]() {
+        MOZ_ASSERT(NS_IsMainThread());
+
+        RefPtr<StorageActivityService> service = GetOrCreate();
+        if (NS_WARN_IF(!service)) {
+          return;
+        }
+
+        service->SendActivityInternal(origin);
+      });
+
+  if (NS_IsMainThread()) {
+    Unused << r->Run();
+  } else {
+    SchedulerGroup::Dispatch(TaskCategory::Other, r.forget());
+  }
+}
+
+/* static */
+already_AddRefed<StorageActivityService> StorageActivityService::GetOrCreate() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (!gStorageActivityService && !gStorageActivityShutdown) {
+    RefPtr<StorageActivityService> service = new StorageActivityService();
+
+    nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+    if (NS_WARN_IF(!obs)) {
+      return nullptr;
+    }
+
+    nsresult rv =
+        obs->AddObserver(service, NS_XPCOM_SHUTDOWN_OBSERVER_ID, true);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return nullptr;
+    }
+
+    gStorageActivityService = service;
+  }
+
+  RefPtr<StorageActivityService> service = gStorageActivityService;
+  return service.forget();
+}
+
+StorageActivityService::StorageActivityService() {
+  MOZ_ASSERT(NS_IsMainThread());
+}
+
+StorageActivityService::~StorageActivityService() {
+  MOZ_ASSERT(NS_IsMainThread());
+}
+
+void StorageActivityService::SendActivityInternal(nsIPrincipal* aPrincipal) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aPrincipal);
+  MOZ_ASSERT(BasePrincipal::Cast(aPrincipal)->Kind() ==
+             BasePrincipal::eContentPrincipal);
+
+  if (!XRE_IsParentProcess()) {
+    SendActivityToParent(aPrincipal);
+    return;
+  }
+
+  nsAutoCString origin;
+  nsresult rv = aPrincipal->GetOrigin(origin);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return;
+  }
+
+  SendActivityInternal(origin);
+}
+
+void StorageActivityService::SendActivityInternal(const nsACString& aOrigin) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  bool shouldAddObserver = mActivities.Count() == 0;
+  mActivities.InsertOrUpdate(aOrigin, PR_Now());
+
+  if (shouldAddObserver) {
+    nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+    if (NS_WARN_IF(!obs)) {
+      return;
+    }
+
+    obs->AddObserver(this, OBSERVER_TOPIC_IDLE_DAILY, true);
+  }
+}
+
+void StorageActivityService::SendActivityToParent(nsIPrincipal* aPrincipal) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!XRE_IsParentProcess());
+
+  ::mozilla::ipc::PBackgroundChild* actor =
+      ::mozilla::ipc::BackgroundChild::GetOrCreateForCurrentThread();
+  if (NS_WARN_IF(!actor)) {
+    return;
+  }
+
+  mozilla::ipc::PrincipalInfo principalInfo;
+  nsresult rv =
+      mozilla::ipc::PrincipalToPrincipalInfo(aPrincipal, &principalInfo);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return;
+  }
+
+  actor->SendStorageActivity(principalInfo);
+}
+
+NS_IMETHODIMP
+StorageActivityService::Observe(nsISupports* aSubject, const char* aTopic,
+                                const char16_t* aData) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (!strcmp(aTopic, OBSERVER_TOPIC_IDLE_DAILY)) {
+    CleanUp();
+    return NS_OK;
+  }
+
+  MOZ_ASSERT(!strcmp(aTopic, NS_XPCOM_SHUTDOWN_OBSERVER_ID));
+
+  gStorageActivityShutdown = true;
+  gStorageActivityService = nullptr;
+  return NS_OK;
+}
+
+void StorageActivityService::CleanUp() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  uint64_t now = PR_Now();
+
+  for (auto iter = mActivities.Iter(); !iter.Done(); iter.Next()) {
+    if ((now - iter.UserData()) / PR_USEC_PER_SEC > TIME_MAX_SECS) {
+      iter.Remove();
+    }
+  }
+
+  // If no activities, remove the observer.
+  if (mActivities.Count() == 0) {
+    nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+    if (obs) {
+      obs->RemoveObserver(this, OBSERVER_TOPIC_IDLE_DAILY);
+    }
+  }
+}
+
+NS_IMETHODIMP
+StorageActivityService::GetActiveOrigins(PRTime aFrom, PRTime aTo,
+                                         nsIArray** aRetval) {
+  uint64_t now = PR_Now();
+  if (((now - aFrom) / PR_USEC_PER_SEC) > TIME_MAX_SECS || aFrom >= aTo) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  // Remove expired entries first.
+  CleanUp();
+
+  nsresult rv = NS_OK;
+  nsCOMPtr<nsIMutableArray> devices =
+      do_CreateInstance(NS_ARRAY_CONTRACTID, &rv);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  for (const auto& activityEntry : mActivities) {
+    if (activityEntry.GetData() >= aFrom && activityEntry.GetData() <= aTo) {
+      RefPtr<BasePrincipal> principal =
+          BasePrincipal::CreateContentPrincipal(activityEntry.GetKey());
+      MOZ_ASSERT(principal);
+
+      rv = devices->AppendElement(principal);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+    }
+  }
+
+  devices.forget(aRetval);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+StorageActivityService::MoveOriginInTime(nsIPrincipal* aPrincipal,
+                                         PRTime aWhen) {
+  if (!XRE_IsParentProcess()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsAutoCString origin;
+  nsresult rv = aPrincipal->GetOrigin(origin);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  mActivities.InsertOrUpdate(origin, aWhen / PR_USEC_PER_SEC);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+StorageActivityService::TestOnlyReset() {
+  mActivities.Clear();
+  return NS_OK;
+}
+
+NS_INTERFACE_MAP_BEGIN(StorageActivityService)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIStorageActivityService)
+  NS_INTERFACE_MAP_ENTRY(nsIStorageActivityService)
+  NS_INTERFACE_MAP_ENTRY(nsIObserver)
+  NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_ADDREF(StorageActivityService)
+NS_IMPL_RELEASE(StorageActivityService)
+
+}  // namespace mozilla::dom
diff --git a/dom/storage/StorageActivityService.h b/dom/storage/StorageActivityService.h
new file mode 100644
index 0000000000..0b61bd128a
--- /dev/null
+++ b/dom/storage/StorageActivityService.h
@@ -0,0 +1,62 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_dom_StorageActivityService_h
+#define mozilla_dom_StorageActivityService_h
+
+#include "nsTHashMap.h"
+#include "nsIObserver.h"
+#include "nsIStorageActivityService.h"
+#include "nsWeakReference.h"
+
+namespace mozilla {
+
+namespace ipc {
+class PrincipalInfo;
+}  // namespace ipc
+
+namespace dom {
+
+class StorageActivityService final : public nsIStorageActivityService,
+                                     public nsIObserver,
+                                     public nsSupportsWeakReference {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSISTORAGEACTIVITYSERVICE
+  NS_DECL_NSIOBSERVER
+
+  // Main-thread only.
+  static void SendActivity(nsIPrincipal* aPrincipal);
+
+  // Thread-safe.
+  static void SendActivity(const mozilla::ipc::PrincipalInfo& aPrincipalInfo);
+
+  // Thread-safe but for parent process only!
+  static void SendActivity(const nsACString& aOrigin);
+
+  // Used by XPCOM. Don't use it, use SendActivity() instead.
+  static already_AddRefed<StorageActivityService> GetOrCreate();
+
+ private:
+  StorageActivityService();
+  ~StorageActivityService();
+
+  void SendActivityInternal(nsIPrincipal* aPrincipal);
+
+  void SendActivityInternal(const nsACString& aOrigin);
+
+  void SendActivityToParent(nsIPrincipal* aPrincipal);
+
+  void CleanUp();
+
+  // Activities grouped by origin (+OriginAttributes).
+  nsTHashMap<nsCStringHashKey, PRTime> mActivities;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_StorageActivityService_h
diff --git a/dom/storage/StorageCommon.h b/dom/storage/StorageCommon.h
new file mode 100644
index 0000000000..633a97805e
--- /dev/null
+++ b/dom/storage/StorageCommon.h
@@ -0,0 +1,18 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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 DOM_STORAGE_STORAGECOMMON_H_
+#define DOM_STORAGE_STORAGECOMMON_H_
+
+#include "mozilla/Types.h"
+
+namespace mozilla::dom {
+
+constexpr uint32_t kPrivateBrowsingIdCount = 2;
+
+}  // namespace mozilla::dom
+
+#endif  // DOM_STORAGE_STORAGECOMMON_H_
diff --git a/dom/storage/StorageDBThread.cpp b/dom/storage/StorageDBThread.cpp
new file mode 100644
index 0000000000..840fb219b9
--- /dev/null
+++ b/dom/storage/StorageDBThread.cpp
@@ -0,0 +1,1626 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "StorageDBThread.h"
+
+#include "StorageCommon.h"
+#include "StorageDBUpdater.h"
+#include "StorageUtils.h"
+#include "LocalStorageCache.h"
+#include "LocalStorageManager.h"
+
+#include "nsComponentManagerUtils.h"
+#include "nsDirectoryServiceUtils.h"
+#include "nsAppDirectoryServiceDefs.h"
+#include "nsThreadUtils.h"
+#include "nsProxyRelease.h"
+#include "mozStorageCID.h"
+#include "mozStorageHelper.h"
+#include "mozIStorageService.h"
+#include "mozIStorageBindingParams.h"
+#include "mozIStorageValueArray.h"
+#include "mozIStorageFunction.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/ipc/BackgroundParent.h"
+#include "nsIObserverService.h"
+#include "nsThread.h"
+#include "nsThreadManager.h"
+#include "nsVariant.h"
+#include "mozilla/EventQueue.h"
+#include "mozilla/IOInterposer.h"
+#include "mozilla/OriginAttributes.h"
+#include "mozilla/ThreadEventQueue.h"
+#include "mozilla/Services.h"
+#include "mozilla/Tokenizer.h"
+#include "GeckoProfiler.h"
+
+// How long we collect write oprerations
+// before they are flushed to the database
+// In milliseconds.
+#define FLUSHING_INTERVAL_MS 5000
+
+// Write Ahead Log's maximum size is 512KB
+#define MAX_WAL_SIZE_BYTES 512 * 1024
+
+// Current version of the database schema
+#define CURRENT_SCHEMA_VERSION 2
+
+namespace mozilla::dom {
+
+using namespace StorageUtils;
+
+namespace {  // anon
+
+StorageDBThread* sStorageThread[kPrivateBrowsingIdCount] = {nullptr, nullptr};
+
+// False until we shut the storage thread down.
+bool sStorageThreadDown[kPrivateBrowsingIdCount] = {false, false};
+
+}  // namespace
+
+// XXX Fix me!
+#if 0
+StorageDBBridge::StorageDBBridge()
+{
+}
+#endif
+
+class StorageDBThread::InitHelper final : public Runnable {
+  nsCOMPtr<nsIEventTarget> mOwningThread;
+  mozilla::Mutex mMutex MOZ_UNANNOTATED;
+  mozilla::CondVar mCondVar;
+  nsString mProfilePath;
+  nsresult mMainThreadResultCode;
+  bool mWaiting;
+
+ public:
+  InitHelper()
+      : Runnable("dom::StorageDBThread::InitHelper"),
+        mOwningThread(GetCurrentSerialEventTarget()),
+        mMutex("InitHelper::mMutex"),
+        mCondVar(mMutex, "InitHelper::mCondVar"),
+        mMainThreadResultCode(NS_OK),
+        mWaiting(true) {}
+
+  // Because of the `sync Preload` IPC, we need to be able to synchronously
+  // initialize, which includes consulting and initializing
+  // some main-thread-only APIs. Bug 1386441 discusses improving this situation.
+  nsresult SyncDispatchAndReturnProfilePath(nsAString& aProfilePath);
+
+ private:
+  ~InitHelper() override = default;
+
+  nsresult RunOnMainThread();
+
+  NS_DECL_NSIRUNNABLE
+};
+
+class StorageDBThread::NoteBackgroundThreadRunnable final : public Runnable {
+  // Expected to be only 0 or 1.
+  const uint32_t mPrivateBrowsingId;
+  nsCOMPtr<nsIEventTarget> mOwningThread;
+
+ public:
+  explicit NoteBackgroundThreadRunnable(const uint32_t aPrivateBrowsingId)
+      : Runnable("dom::StorageDBThread::NoteBackgroundThreadRunnable"),
+        mPrivateBrowsingId(aPrivateBrowsingId),
+        mOwningThread(GetCurrentSerialEventTarget()) {
+    MOZ_RELEASE_ASSERT(aPrivateBrowsingId < kPrivateBrowsingIdCount);
+  }
+
+ private:
+  ~NoteBackgroundThreadRunnable() override = default;
+
+  NS_DECL_NSIRUNNABLE
+};
+
+StorageDBThread::StorageDBThread(const uint32_t aPrivateBrowsingId)
+    : mThread(nullptr),
+      mThreadObserver(new ThreadObserver()),
+      mStopIOThread(false),
+      mWALModeEnabled(false),
+      mDBReady(false),
+      mStatus(NS_OK),
+      mWorkerStatements(mWorkerConnection),
+      mReaderStatements(mReaderConnection),
+      mFlushImmediately(false),
+      mPrivateBrowsingId(aPrivateBrowsingId),
+      mPriorityCounter(0) {
+  MOZ_RELEASE_ASSERT(aPrivateBrowsingId < kPrivateBrowsingIdCount);
+}
+
+// static
+StorageDBThread* StorageDBThread::Get(const uint32_t aPrivateBrowsingId) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_RELEASE_ASSERT(aPrivateBrowsingId < kPrivateBrowsingIdCount);
+
+  return sStorageThread[aPrivateBrowsingId];
+}
+
+// static
+StorageDBThread* StorageDBThread::GetOrCreate(
+    const nsString& aProfilePath, const uint32_t aPrivateBrowsingId) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_RELEASE_ASSERT(aPrivateBrowsingId < kPrivateBrowsingIdCount);
+
+  StorageDBThread*& storageThread = sStorageThread[aPrivateBrowsingId];
+  if (storageThread || sStorageThreadDown[aPrivateBrowsingId]) {
+    // When sStorageThreadDown is at true, sStorageThread is null.
+    // Checking sStorageThreadDown flag here prevents reinitialization of
+    // the storage thread after shutdown.
+    return storageThread;
+  }
+
+  auto newStorageThread = MakeUnique<StorageDBThread>(aPrivateBrowsingId);
+
+  nsresult rv = newStorageThread->Init(aProfilePath);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return nullptr;
+  }
+
+  storageThread = newStorageThread.release();
+
+  return storageThread;
+}
+
+// static
+nsresult StorageDBThread::GetProfilePath(nsString& aProfilePath) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  MOZ_ASSERT(NS_IsMainThread());
+
+  // Need to determine location on the main thread, since
+  // NS_GetSpecialDirectory accesses the atom table that can
+  // only be accessed on the main thread.
+  nsCOMPtr<nsIFile> profileDir;
+  nsresult rv = NS_GetSpecialDirectory(NS_APP_USER_PROFILE_50_DIR,
+                                       getter_AddRefs(profileDir));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = profileDir->GetPath(aProfilePath);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // This service has to be started on the main thread currently.
+  nsCOMPtr<mozIStorageService> ss =
+      do_GetService(MOZ_STORAGE_SERVICE_CONTRACTID, &rv);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+nsresult StorageDBThread::Init(const nsString& aProfilePath) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  if (mPrivateBrowsingId == 0) {
+    nsresult rv;
+
+    nsString profilePath;
+    if (aProfilePath.IsEmpty()) {
+      RefPtr<InitHelper> helper = new InitHelper();
+
+      rv = helper->SyncDispatchAndReturnProfilePath(profilePath);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+    } else {
+      profilePath = aProfilePath;
+    }
+
+    mDatabaseFile = do_CreateInstance(NS_LOCAL_FILE_CONTRACTID, &rv);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    rv = mDatabaseFile->InitWithPath(profilePath);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    rv = mDatabaseFile->Append(u"webappsstore.sqlite"_ns);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  // Need to keep the lock to avoid setting mThread later then
+  // the thread body executes.
+  MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+
+  mThread = PR_CreateThread(PR_USER_THREAD, &StorageDBThread::ThreadFunc, this,
+                            PR_PRIORITY_LOW, PR_GLOBAL_THREAD,
+                            PR_JOINABLE_THREAD, 262144);
+  if (!mThread) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  RefPtr<NoteBackgroundThreadRunnable> runnable =
+      new NoteBackgroundThreadRunnable(mPrivateBrowsingId);
+  MOZ_ALWAYS_SUCCEEDS(NS_DispatchToMainThread(runnable));
+
+  return NS_OK;
+}
+
+nsresult StorageDBThread::Shutdown() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  if (!mThread) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  Telemetry::AutoTimer<Telemetry::LOCALDOMSTORAGE_SHUTDOWN_DATABASE_MS> timer;
+
+  {
+    MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+
+    // After we stop, no other operations can be accepted
+    mFlushImmediately = true;
+    mStopIOThread = true;
+    monitor.Notify();
+  }
+
+  PR_JoinThread(mThread);
+  mThread = nullptr;
+
+  return mStatus;
+}
+
+void StorageDBThread::SyncPreload(LocalStorageCacheBridge* aCache,
+                                  bool aForceSync) {
+  AUTO_PROFILER_LABEL("StorageDBThread::SyncPreload", OTHER);
+  if (!aForceSync && aCache->LoadedCount()) {
+    // Preload already started for this cache, just wait for it to finish.
+    // LoadWait will exit after LoadDone on the cache has been called.
+    SetHigherPriority();
+    aCache->LoadWait();
+    SetDefaultPriority();
+    return;
+  }
+
+  // Bypass sync load when an update is pending in the queue to write, we would
+  // get incosistent data in the cache.  Also don't allow sync main-thread
+  // preload when DB open and init is still pending on the background thread.
+  if (mDBReady && mWALModeEnabled) {
+    bool pendingTasks;
+    {
+      MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+      pendingTasks = mPendingTasks.IsOriginUpdatePending(
+                         aCache->OriginSuffix(), aCache->OriginNoSuffix()) ||
+                     mPendingTasks.IsOriginClearPending(
+                         aCache->OriginSuffix(), aCache->OriginNoSuffix());
+    }
+
+    if (!pendingTasks) {
+      // WAL is enabled, thus do the load synchronously on the main thread.
+      DBOperation preload(DBOperation::opPreload, aCache);
+      preload.PerformAndFinalize(this);
+      return;
+    }
+  }
+
+  // Need to go asynchronously since WAL is not allowed or scheduled updates
+  // need to be flushed first.
+  // Schedule preload for this cache as the first operation.
+  nsresult rv =
+      InsertDBOp(MakeUnique<DBOperation>(DBOperation::opPreloadUrgent, aCache));
+
+  // LoadWait exits after LoadDone of the cache has been called.
+  if (NS_SUCCEEDED(rv)) {
+    aCache->LoadWait();
+  }
+}
+
+void StorageDBThread::AsyncFlush() {
+  MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+  mFlushImmediately = true;
+  monitor.Notify();
+}
+
+bool StorageDBThread::ShouldPreloadOrigin(const nsACString& aOrigin) {
+  MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+  return mOriginsHavingData.Contains(aOrigin);
+}
+
+void StorageDBThread::GetOriginsHavingData(nsTArray<nsCString>* aOrigins) {
+  MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+  AppendToArray(*aOrigins, mOriginsHavingData);
+}
+
+nsresult StorageDBThread::InsertDBOp(
+    UniquePtr<StorageDBThread::DBOperation> aOperation) {
+  MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+
+  if (NS_FAILED(mStatus)) {
+    MonitorAutoUnlock unlock(mThreadObserver->GetMonitor());
+    aOperation->Finalize(mStatus);
+    return mStatus;
+  }
+
+  if (mStopIOThread) {
+    // Thread use after shutdown demanded.
+    MOZ_ASSERT(false);
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+
+  switch (aOperation->Type()) {
+    case DBOperation::opPreload:
+    case DBOperation::opPreloadUrgent:
+      if (mPendingTasks.IsOriginUpdatePending(aOperation->OriginSuffix(),
+                                              aOperation->OriginNoSuffix())) {
+        // If there is a pending update operation for the scope first do the
+        // flush before we preload the cache.  This may happen in an extremely
+        // rare case when a child process throws away its cache before flush on
+        // the parent has finished.  If we would preloaded the cache as a
+        // priority operation before the pending flush, we would have got an
+        // inconsistent cache content.
+        mFlushImmediately = true;
+      } else if (mPendingTasks.IsOriginClearPending(
+                     aOperation->OriginSuffix(),
+                     aOperation->OriginNoSuffix())) {
+        // The scope is scheduled to be cleared, so just quickly load as empty.
+        // We need to do this to prevent load of the DB data before the scope
+        // has actually been cleared from the database.  Preloads are processed
+        // immediately before update and clear operations on the database that
+        // are flushed periodically in batches.
+        MonitorAutoUnlock unlock(mThreadObserver->GetMonitor());
+        aOperation->Finalize(NS_OK);
+        return NS_OK;
+      }
+      [[fallthrough]];
+
+    case DBOperation::opGetUsage:
+      if (aOperation->Type() == DBOperation::opPreloadUrgent) {
+        SetHigherPriority();  // Dropped back after urgent preload execution
+        mPreloads.InsertElementAt(0, aOperation.release());
+      } else {
+        mPreloads.AppendElement(aOperation.release());
+      }
+
+      // Immediately start executing this.
+      monitor.Notify();
+      break;
+
+    default:
+      // Update operations are first collected, coalesced and then flushed
+      // after a short time.
+      mPendingTasks.Add(std::move(aOperation));
+
+      ScheduleFlush();
+      break;
+  }
+
+  return NS_OK;
+}
+
+void StorageDBThread::SetHigherPriority() {
+  ++mPriorityCounter;
+  PR_SetThreadPriority(mThread, PR_PRIORITY_URGENT);
+}
+
+void StorageDBThread::SetDefaultPriority() {
+  if (--mPriorityCounter <= 0) {
+    PR_SetThreadPriority(mThread, PR_PRIORITY_LOW);
+  }
+}
+
+void StorageDBThread::ThreadFunc(void* aArg) {
+  {
+    auto queue = MakeRefPtr<ThreadEventQueue>(MakeUnique<EventQueue>());
+    Unused << nsThreadManager::get().CreateCurrentThread(
+        queue, nsThread::NOT_MAIN_THREAD);
+  }
+
+  AUTO_PROFILER_REGISTER_THREAD("localStorage DB");
+  NS_SetCurrentThreadName("localStorage DB");
+  mozilla::IOInterposer::RegisterCurrentThread();
+
+  StorageDBThread* thread = static_cast<StorageDBThread*>(aArg);
+  thread->ThreadFunc();
+  mozilla::IOInterposer::UnregisterCurrentThread();
+}
+
+void StorageDBThread::ThreadFunc() {
+  nsresult rv = InitDatabase();
+
+  MonitorAutoLock lockMonitor(mThreadObserver->GetMonitor());
+
+  if (NS_FAILED(rv)) {
+    mStatus = rv;
+    mStopIOThread = true;
+    return;
+  }
+
+  // Create an nsIThread for the current PRThread, so we can observe runnables
+  // dispatched to it.
+  nsCOMPtr<nsIThread> thread = NS_GetCurrentThread();
+  nsCOMPtr<nsIThreadInternal> threadInternal = do_QueryInterface(thread);
+  MOZ_ASSERT(threadInternal);  // Should always succeed.
+  threadInternal->SetObserver(mThreadObserver);
+
+  while (MOZ_LIKELY(!mStopIOThread || mPreloads.Length() ||
+                    mPendingTasks.HasTasks() ||
+                    mThreadObserver->HasPendingEvents())) {
+    // Process xpcom events first.
+    while (MOZ_UNLIKELY(mThreadObserver->HasPendingEvents())) {
+      mThreadObserver->ClearPendingEvents();
+      MonitorAutoUnlock unlock(mThreadObserver->GetMonitor());
+      bool processedEvent;
+      do {
+        rv = thread->ProcessNextEvent(false, &processedEvent);
+      } while (NS_SUCCEEDED(rv) && processedEvent);
+    }
+
+    TimeDuration timeUntilFlush = TimeUntilFlush();
+    if (MOZ_UNLIKELY(timeUntilFlush.IsZero())) {
+      // Flush time is up or flush has been forced, do it now.
+      UnscheduleFlush();
+      if (mPendingTasks.Prepare()) {
+        {
+          MonitorAutoUnlock unlockMonitor(mThreadObserver->GetMonitor());
+          rv = mPendingTasks.Execute(this);
+        }
+
+        if (!mPendingTasks.Finalize(rv)) {
+          mStatus = rv;
+          NS_WARNING("localStorage DB access broken");
+        }
+      }
+      NotifyFlushCompletion();
+    } else if (MOZ_LIKELY(mPreloads.Length())) {
+      UniquePtr<DBOperation> op(mPreloads[0]);
+      mPreloads.RemoveElementAt(0);
+      {
+        MonitorAutoUnlock unlockMonitor(mThreadObserver->GetMonitor());
+        op->PerformAndFinalize(this);
+      }
+
+      if (op->Type() == DBOperation::opPreloadUrgent) {
+        SetDefaultPriority();  // urgent preload unscheduled
+      }
+    } else if (MOZ_UNLIKELY(!mStopIOThread)) {
+      AUTO_PROFILER_LABEL("StorageDBThread::ThreadFunc::Wait", IDLE);
+      lockMonitor.Wait(timeUntilFlush);
+    }
+  }  // thread loop
+
+  mStatus = ShutdownDatabase();
+
+  if (threadInternal) {
+    threadInternal->SetObserver(nullptr);
+  }
+}
+
+NS_IMPL_ISUPPORTS(StorageDBThread::ThreadObserver, nsIThreadObserver)
+
+NS_IMETHODIMP
+StorageDBThread::ThreadObserver::OnDispatchedEvent() {
+  MonitorAutoLock lock(mMonitor);
+  mHasPendingEvents = true;
+  lock.Notify();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+StorageDBThread::ThreadObserver::OnProcessNextEvent(nsIThreadInternal* aThread,
+                                                    bool mayWait) {
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+StorageDBThread::ThreadObserver::AfterProcessNextEvent(
+    nsIThreadInternal* aThread, bool eventWasProcessed) {
+  return NS_OK;
+}
+
+nsresult StorageDBThread::OpenDatabaseConnection() {
+  nsresult rv;
+
+  MOZ_ASSERT(!NS_IsMainThread());
+
+  nsCOMPtr<mozIStorageService> service =
+      do_GetService(MOZ_STORAGE_SERVICE_CONTRACTID, &rv);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (mPrivateBrowsingId == 0) {
+    MOZ_ASSERT(mDatabaseFile);
+
+    rv = service->OpenUnsharedDatabase(mDatabaseFile,
+                                       mozIStorageService::CONNECTION_DEFAULT,
+                                       getter_AddRefs(mWorkerConnection));
+    if (rv == NS_ERROR_FILE_CORRUPTED) {
+      // delete the db and try opening again
+      rv = mDatabaseFile->Remove(false);
+      NS_ENSURE_SUCCESS(rv, rv);
+      rv = service->OpenUnsharedDatabase(mDatabaseFile,
+                                         mozIStorageService::CONNECTION_DEFAULT,
+                                         getter_AddRefs(mWorkerConnection));
+    }
+  } else {
+    MOZ_ASSERT(mPrivateBrowsingId == 1);
+
+    rv = service->OpenSpecialDatabase(kMozStorageMemoryStorageKey,
+                                      "lsprivatedb"_ns,
+                                      mozIStorageService::CONNECTION_DEFAULT,
+                                      getter_AddRefs(mWorkerConnection));
+  }
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+nsresult StorageDBThread::OpenAndUpdateDatabase() {
+  nsresult rv;
+
+  // Here we are on the worker thread. This opens the worker connection.
+  MOZ_ASSERT(!NS_IsMainThread());
+
+  rv = OpenDatabaseConnection();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // SQLite doesn't support WAL journals for in-memory databases.
+  if (mPrivateBrowsingId == 0) {
+    rv = TryJournalMode();
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  return NS_OK;
+}
+
+nsresult StorageDBThread::InitDatabase() {
+  nsresult rv;
+
+  // Here we are on the worker thread. This opens the worker connection.
+  MOZ_ASSERT(!NS_IsMainThread());
+
+  rv = OpenAndUpdateDatabase();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = StorageDBUpdater::Update(mWorkerConnection);
+  if (NS_FAILED(rv)) {
+    if (mPrivateBrowsingId == 0) {
+      // Update has failed, rather throw the database away and try
+      // opening and setting it up again.
+      rv = mWorkerConnection->Close();
+      mWorkerConnection = nullptr;
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = mDatabaseFile->Remove(false);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = OpenAndUpdateDatabase();
+    }
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  // Create a read-only clone
+  (void)mWorkerConnection->Clone(true, getter_AddRefs(mReaderConnection));
+  NS_ENSURE_TRUE(mReaderConnection, NS_ERROR_FAILURE);
+
+  // Database open and all initiation operation are done.  Switching this flag
+  // to true allow main thread to read directly from the database.  If we would
+  // allow this sooner, we would have opened a window where main thread read
+  // might operate on a totally broken and incosistent database.
+  mDBReady = true;
+
+  // List scopes having any stored data
+  nsCOMPtr<mozIStorageStatement> stmt;
+  // Note: result of this select must match StorageManager::CreateOrigin()
+  rv = mWorkerConnection->CreateStatement(
+      nsLiteralCString("SELECT DISTINCT originAttributes || ':' || originKey "
+                       "FROM webappsstore2"),
+      getter_AddRefs(stmt));
+  NS_ENSURE_SUCCESS(rv, rv);
+  mozStorageStatementScoper scope(stmt);
+
+  bool exists;
+  while (NS_SUCCEEDED(rv = stmt->ExecuteStep(&exists)) && exists) {
+    nsAutoCString foundOrigin;
+    rv = stmt->GetUTF8String(0, foundOrigin);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    MonitorAutoLock monitor(mThreadObserver->GetMonitor());
+    mOriginsHavingData.Insert(foundOrigin);
+  }
+
+  return NS_OK;
+}
+
+nsresult StorageDBThread::SetJournalMode(bool aIsWal) {
+  nsresult rv;
+
+  nsAutoCString stmtString(MOZ_STORAGE_UNIQUIFY_QUERY_STR
+                           "PRAGMA journal_mode = ");
+  if (aIsWal) {
+    stmtString.AppendLiteral("wal");
+  } else {
+    stmtString.AppendLiteral("truncate");
+  }
+
+  nsCOMPtr<mozIStorageStatement> stmt;
+  rv = mWorkerConnection->CreateStatement(stmtString, getter_AddRefs(stmt));
+  NS_ENSURE_SUCCESS(rv, rv);
+  mozStorageStatementScoper scope(stmt);
+
+  bool hasResult = false;
+  rv = stmt->ExecuteStep(&hasResult);
+  NS_ENSURE_SUCCESS(rv, rv);
+  if (!hasResult) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsAutoCString journalMode;
+  rv = stmt->GetUTF8String(0, journalMode);
+  NS_ENSURE_SUCCESS(rv, rv);
+  if ((aIsWal && !journalMode.EqualsLiteral("wal")) ||
+      (!aIsWal && !journalMode.EqualsLiteral("truncate"))) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+nsresult StorageDBThread::TryJournalMode() {
+  nsresult rv;
+
+  rv = SetJournalMode(true);
+  if (NS_FAILED(rv)) {
+    mWALModeEnabled = false;
+
+    rv = SetJournalMode(false);
+    NS_ENSURE_SUCCESS(rv, rv);
+  } else {
+    mWALModeEnabled = true;
+
+    rv = ConfigureWALBehavior();
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  return NS_OK;
+}
+
+nsresult StorageDBThread::ConfigureWALBehavior() {
+  // Get the DB's page size
+  nsCOMPtr<mozIStorageStatement> stmt;
+  nsresult rv = mWorkerConnection->CreateStatement(
+      nsLiteralCString(MOZ_STORAGE_UNIQUIFY_QUERY_STR "PRAGMA page_size"),
+      getter_AddRefs(stmt));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  bool hasResult = false;
+  rv = stmt->ExecuteStep(&hasResult);
+  NS_ENSURE_TRUE(NS_SUCCEEDED(rv) && hasResult, NS_ERROR_FAILURE);
+
+  int32_t pageSize = 0;
+  rv = stmt->GetInt32(0, &pageSize);
+  NS_ENSURE_TRUE(NS_SUCCEEDED(rv) && pageSize > 0, NS_ERROR_UNEXPECTED);
+
+  // Set the threshold for auto-checkpointing the WAL.
+  // We don't want giant logs slowing down reads & shutdown.
+  // Note there is a default journal_size_limit set by mozStorage.
+  int32_t thresholdInPages =
+      static_cast<int32_t>(MAX_WAL_SIZE_BYTES / pageSize);
+  nsAutoCString thresholdPragma("PRAGMA wal_autocheckpoint = ");
+  thresholdPragma.AppendInt(thresholdInPages);
+  rv = mWorkerConnection->ExecuteSimpleSQL(thresholdPragma);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+nsresult StorageDBThread::ShutdownDatabase() {
+  // Has to be called on the worker thread.
+  MOZ_ASSERT(!NS_IsMainThread());
+
+  nsresult rv = mStatus;
+
+  mDBReady = false;
+
+  // Finalize the cached statements.
+  mReaderStatements.FinalizeStatements();
+  mWorkerStatements.FinalizeStatements();
+
+  if (mReaderConnection) {
+    // No need to sync access to mReaderConnection since the main thread
+    // is right now joining this thread, unable to execute any events.
+    mReaderConnection->Close();
+    mReaderConnection = nullptr;
+  }
+
+  if (mWorkerConnection) {
+    rv = mWorkerConnection->Close();
+    mWorkerConnection = nullptr;
+  }
+
+  return rv;
+}
+
+void StorageDBThread::ScheduleFlush() {
+  if (mDirtyEpoch) {
+    return;  // Already scheduled
+  }
+
+  // Must be non-zero to indicate we are scheduled
+  mDirtyEpoch = TimeStamp::Now();
+
+  // Wake the monitor from indefinite sleep...
+  (mThreadObserver->GetMonitor()).Notify();
+}
+
+void StorageDBThread::UnscheduleFlush() {
+  // We are just about to do the flush, drop flags
+  mFlushImmediately = false;
+  mDirtyEpoch = TimeStamp();
+}
+
+TimeDuration StorageDBThread::TimeUntilFlush() {
+  if (mFlushImmediately) {
+    return 0;  // Do it now regardless the timeout.
+  }
+
+  if (!mDirtyEpoch) {
+    return TimeDuration::Forever();  // No pending task...
+  }
+
+  TimeStamp now = TimeStamp::Now();
+  TimeDuration age = now - mDirtyEpoch;
+  static const TimeDuration kMaxAge =
+      TimeDuration::FromMilliseconds(FLUSHING_INTERVAL_MS);
+  if (age > kMaxAge) {
+    return 0;  // It is time.
+  }
+
+  return kMaxAge - age;  // Time left. This is used to sleep the monitor.
+}
+
+void StorageDBThread::NotifyFlushCompletion() {
+#ifdef DOM_STORAGE_TESTS
+  if (!NS_IsMainThread()) {
+    RefPtr<nsRunnableMethod<StorageDBThread, void, false>> event =
+        NewNonOwningRunnableMethod(
+            "dom::StorageDBThread::NotifyFlushCompletion", this,
+            &StorageDBThread::NotifyFlushCompletion);
+    NS_DispatchToMainThread(event);
+    return;
+  }
+
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  if (obs) {
+    obs->NotifyObservers(nullptr, "domstorage-test-flushed", nullptr);
+  }
+#endif
+}
+
+// Helper SQL function classes
+
+namespace {
+
+class OriginAttrsPatternMatchSQLFunction final : public mozIStorageFunction {
+  NS_DECL_ISUPPORTS
+  NS_DECL_MOZISTORAGEFUNCTION
+
+  explicit OriginAttrsPatternMatchSQLFunction(
+      OriginAttributesPattern const& aPattern)
+      : mPattern(aPattern) {}
+
+ private:
+  OriginAttrsPatternMatchSQLFunction() = delete;
+  ~OriginAttrsPatternMatchSQLFunction() = default;
+
+  OriginAttributesPattern mPattern;
+};
+
+NS_IMPL_ISUPPORTS(OriginAttrsPatternMatchSQLFunction, mozIStorageFunction)
+
+NS_IMETHODIMP
+OriginAttrsPatternMatchSQLFunction::OnFunctionCall(
+    mozIStorageValueArray* aFunctionArguments, nsIVariant** aResult) {
+  nsresult rv;
+
+  nsAutoCString suffix;
+  rv = aFunctionArguments->GetUTF8String(0, suffix);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  OriginAttributes oa;
+  bool success = oa.PopulateFromSuffix(suffix);
+  NS_ENSURE_TRUE(success, NS_ERROR_FAILURE);
+  bool result = mPattern.Matches(oa);
+
+  RefPtr<nsVariant> outVar(new nsVariant());
+  rv = outVar->SetAsBool(result);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  outVar.forget(aResult);
+  return NS_OK;
+}
+
+}  // namespace
+
+// StorageDBThread::DBOperation
+
+StorageDBThread::DBOperation::DBOperation(const OperationType aType,
+                                          LocalStorageCacheBridge* aCache,
+                                          const nsAString& aKey,
+                                          const nsAString& aValue)
+    : mType(aType), mCache(aCache), mKey(aKey), mValue(aValue) {
+  MOZ_ASSERT(mType == opPreload || mType == opPreloadUrgent ||
+             mType == opAddItem || mType == opUpdateItem ||
+             mType == opRemoveItem || mType == opClear || mType == opClearAll);
+  MOZ_COUNT_CTOR(StorageDBThread::DBOperation);
+}
+
+StorageDBThread::DBOperation::DBOperation(const OperationType aType,
+                                          StorageUsageBridge* aUsage)
+    : mType(aType), mUsage(aUsage) {
+  MOZ_ASSERT(mType == opGetUsage);
+  MOZ_COUNT_CTOR(StorageDBThread::DBOperation);
+}
+
+StorageDBThread::DBOperation::DBOperation(const OperationType aType,
+                                          const nsACString& aOriginNoSuffix)
+    : mType(aType), mCache(nullptr), mOrigin(aOriginNoSuffix) {
+  MOZ_ASSERT(mType == opClearMatchingOrigin);
+  MOZ_COUNT_CTOR(StorageDBThread::DBOperation);
+}
+
+StorageDBThread::DBOperation::DBOperation(
+    const OperationType aType, const OriginAttributesPattern& aOriginNoSuffix)
+    : mType(aType), mCache(nullptr), mOriginPattern(aOriginNoSuffix) {
+  MOZ_ASSERT(mType == opClearMatchingOriginAttributes);
+  MOZ_COUNT_CTOR(StorageDBThread::DBOperation);
+}
+
+StorageDBThread::DBOperation::~DBOperation() {
+  MOZ_COUNT_DTOR(StorageDBThread::DBOperation);
+}
+
+const nsCString StorageDBThread::DBOperation::OriginNoSuffix() const {
+  if (mCache) {
+    return mCache->OriginNoSuffix();
+  }
+
+  return ""_ns;
+}
+
+const nsCString StorageDBThread::DBOperation::OriginSuffix() const {
+  if (mCache) {
+    return mCache->OriginSuffix();
+  }
+
+  return ""_ns;
+}
+
+const nsCString StorageDBThread::DBOperation::Origin() const {
+  if (mCache) {
+    return mCache->Origin();
+  }
+
+  return mOrigin;
+}
+
+const nsCString StorageDBThread::DBOperation::Target() const {
+  switch (mType) {
+    case opAddItem:
+    case opUpdateItem:
+    case opRemoveItem:
+      return Origin() + "|"_ns + NS_ConvertUTF16toUTF8(mKey);
+
+    default:
+      return Origin();
+  }
+}
+
+void StorageDBThread::DBOperation::PerformAndFinalize(
+    StorageDBThread* aThread) {
+  Finalize(Perform(aThread));
+}
+
+nsresult StorageDBThread::DBOperation::Perform(StorageDBThread* aThread) {
+  nsresult rv;
+
+  switch (mType) {
+    case opPreload:
+    case opPreloadUrgent: {
+      // Already loaded?
+      if (mCache->Loaded()) {
+        break;
+      }
+
+      StatementCache* statements;
+      if (MOZ_UNLIKELY(::mozilla::ipc::IsOnBackgroundThread())) {
+        statements = &aThread->mReaderStatements;
+      } else {
+        statements = &aThread->mWorkerStatements;
+      }
+
+      // OFFSET is an optimization when we have to do a sync load
+      // and cache has already loaded some parts asynchronously.
+      // It skips keys we have already loaded.
+      nsCOMPtr<mozIStorageStatement> stmt = statements->GetCachedStatement(
+          "SELECT key, value FROM webappsstore2 "
+          "WHERE originAttributes = :originAttributes AND originKey = "
+          ":originKey "
+          "ORDER BY key LIMIT -1 OFFSET :offset");
+      NS_ENSURE_STATE(stmt);
+      mozStorageStatementScoper scope(stmt);
+
+      rv = stmt->BindUTF8StringByName("originAttributes"_ns,
+                                      mCache->OriginSuffix());
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = stmt->BindUTF8StringByName("originKey"_ns, mCache->OriginNoSuffix());
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = stmt->BindInt32ByName("offset"_ns,
+                                 static_cast<int32_t>(mCache->LoadedCount()));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      bool exists;
+      while (NS_SUCCEEDED(rv = stmt->ExecuteStep(&exists)) && exists) {
+        nsAutoString key;
+        rv = stmt->GetString(0, key);
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        nsAutoString value;
+        rv = stmt->GetString(1, value);
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        if (!mCache->LoadItem(key, value)) {
+          break;
+        }
+      }
+      // The loop condition's call to ExecuteStep() may have terminated because
+      // !NS_SUCCEEDED(), we need an early return to cover that case.  This also
+      // covers success cases as well, but that's inductively safe.
+      NS_ENSURE_SUCCESS(rv, rv);
+      break;
+    }
+
+    case opGetUsage: {
+      // Bug 1676410 fixed a regression caused by bug 1165214. However, it
+      // turns out that 100% correct checking of the eTLD+1 usage is not
+      // possible to recover easily, see bug 1683299.
+#if 0
+      // This is how it should be done, but due to other problems like lack
+      // of usage synchronization between content processes, we temporarily
+      // disabled the matching using "%".
+
+      nsCOMPtr<mozIStorageStatement> stmt =
+          aThread->mWorkerStatements.GetCachedStatement(
+              "SELECT SUM(LENGTH(key) + LENGTH(value)) FROM webappsstore2 "
+              "WHERE (originAttributes || ':' || originKey) LIKE :usageOrigin "
+              "ESCAPE '\\'");
+      NS_ENSURE_STATE(stmt);
+
+      mozStorageStatementScoper scope(stmt);
+
+      // The database schema is built around cleverly reversing domain names
+      // (the "originKey") so that we can efficiently group usage by eTLD+1.
+      // "foo.example.org" has an eTLD+1 of ".example.org". They reverse to
+      // "gro.elpmaxe.oof" and "gro.elpmaxe." respectively, noting that the
+      // reversed eTLD+1 is a prefix of its reversed sub-domain. To this end,
+      // we can calculate all of the usage for an eTLD+1 by summing up all the
+      // rows which have the reversed eTLD+1 as a prefix. In SQL we can
+      // accomplish this using LIKE which provides for case-insensitive
+      // matching with "_" as a single-character wildcard match and "%" any
+      // sequence of zero or more characters. So by suffixing the reversed
+      // eTLD+1 and using "%" we get our case-insensitive (domain names are
+      // case-insensitive) matching. Note that although legal domain names
+      // don't include "_" or "%", file origins can include them, so we need
+      // to escape our OriginScope for correctness.
+      nsAutoCString originScopeEscaped;
+      rv = stmt->EscapeUTF8StringForLIKE(mUsage->OriginScope(), '\\',
+                                         originScopeEscaped);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = stmt->BindUTF8StringByName("usageOrigin"_ns,
+                                      originScopeEscaped + "%"_ns);
+      NS_ENSURE_SUCCESS(rv, rv);
+#else
+      // This is the code before bug 1676410 and bug 1676973. The returned
+      // usage will be zero in most of the cases, but due to lack of usage
+      // synchronization between content processes we have to live with this
+      // semi-broken behaviour because it causes less harm than the matching
+      // using "%".
+
+      nsCOMPtr<mozIStorageStatement> stmt =
+          aThread->mWorkerStatements.GetCachedStatement(
+              "SELECT SUM(LENGTH(key) + LENGTH(value)) FROM webappsstore2 "
+              "WHERE (originAttributes || ':' || originKey) LIKE :usageOrigin");
+      NS_ENSURE_STATE(stmt);
+
+      mozStorageStatementScoper scope(stmt);
+
+      rv = stmt->BindUTF8StringByName("usageOrigin"_ns, mUsage->OriginScope());
+      NS_ENSURE_SUCCESS(rv, rv);
+#endif
+
+      bool exists;
+      rv = stmt->ExecuteStep(&exists);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      int64_t usage = 0;
+      if (exists) {
+        rv = stmt->GetInt64(0, &usage);
+        NS_ENSURE_SUCCESS(rv, rv);
+      }
+
+      mUsage->LoadUsage(usage);
+      break;
+    }
+
+    case opAddItem:
+    case opUpdateItem: {
+      MOZ_ASSERT(!NS_IsMainThread());
+
+      nsCOMPtr<mozIStorageStatement> stmt =
+          aThread->mWorkerStatements.GetCachedStatement(
+              "INSERT OR REPLACE INTO webappsstore2 (originAttributes, "
+              "originKey, scope, key, value) "
+              "VALUES (:originAttributes, :originKey, :scope, :key, :value) ");
+      NS_ENSURE_STATE(stmt);
+
+      mozStorageStatementScoper scope(stmt);
+
+      rv = stmt->BindUTF8StringByName("originAttributes"_ns,
+                                      mCache->OriginSuffix());
+      NS_ENSURE_SUCCESS(rv, rv);
+      rv = stmt->BindUTF8StringByName("originKey"_ns, mCache->OriginNoSuffix());
+      NS_ENSURE_SUCCESS(rv, rv);
+      // Filling the 'scope' column just for downgrade compatibility reasons
+      rv = stmt->BindUTF8StringByName(
+          "scope"_ns,
+          Scheme0Scope(mCache->OriginSuffix(), mCache->OriginNoSuffix()));
+      NS_ENSURE_SUCCESS(rv, rv);
+      rv = stmt->BindStringByName("key"_ns, mKey);
+      NS_ENSURE_SUCCESS(rv, rv);
+      rv = stmt->BindStringByName("value"_ns, mValue);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = stmt->Execute();
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      MonitorAutoLock monitor(aThread->mThreadObserver->GetMonitor());
+      aThread->mOriginsHavingData.Insert(Origin());
+      break;
+    }
+
+    case opRemoveItem: {
+      MOZ_ASSERT(!NS_IsMainThread());
+
+      nsCOMPtr<mozIStorageStatement> stmt =
+          aThread->mWorkerStatements.GetCachedStatement(
+              "DELETE FROM webappsstore2 "
+              "WHERE originAttributes = :originAttributes AND originKey = "
+              ":originKey "
+              "AND key = :key ");
+      NS_ENSURE_STATE(stmt);
+      mozStorageStatementScoper scope(stmt);
+
+      rv = stmt->BindUTF8StringByName("originAttributes"_ns,
+                                      mCache->OriginSuffix());
+      NS_ENSURE_SUCCESS(rv, rv);
+      rv = stmt->BindUTF8StringByName("originKey"_ns, mCache->OriginNoSuffix());
+      NS_ENSURE_SUCCESS(rv, rv);
+      rv = stmt->BindStringByName("key"_ns, mKey);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = stmt->Execute();
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      break;
+    }
+
+    case opClear: {
+      MOZ_ASSERT(!NS_IsMainThread());
+
+      nsCOMPtr<mozIStorageStatement> stmt =
+          aThread->mWorkerStatements.GetCachedStatement(
+              "DELETE FROM webappsstore2 "
+              "WHERE originAttributes = :originAttributes AND originKey = "
+              ":originKey");
+      NS_ENSURE_STATE(stmt);
+      mozStorageStatementScoper scope(stmt);
+
+      rv = stmt->BindUTF8StringByName("originAttributes"_ns,
+                                      mCache->OriginSuffix());
+      NS_ENSURE_SUCCESS(rv, rv);
+      rv = stmt->BindUTF8StringByName("originKey"_ns, mCache->OriginNoSuffix());
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = stmt->Execute();
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      MonitorAutoLock monitor(aThread->mThreadObserver->GetMonitor());
+      aThread->mOriginsHavingData.Remove(Origin());
+      break;
+    }
+
+    case opClearAll: {
+      MOZ_ASSERT(!NS_IsMainThread());
+
+      nsCOMPtr<mozIStorageStatement> stmt =
+          aThread->mWorkerStatements.GetCachedStatement(
+              "DELETE FROM webappsstore2");
+      NS_ENSURE_STATE(stmt);
+      mozStorageStatementScoper scope(stmt);
+
+      rv = stmt->Execute();
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      MonitorAutoLock monitor(aThread->mThreadObserver->GetMonitor());
+      aThread->mOriginsHavingData.Clear();
+      break;
+    }
+
+    case opClearMatchingOrigin: {
+      MOZ_ASSERT(!NS_IsMainThread());
+
+      nsCOMPtr<mozIStorageStatement> stmt =
+          aThread->mWorkerStatements.GetCachedStatement(
+              "DELETE FROM webappsstore2"
+              " WHERE originKey GLOB :scope");
+      NS_ENSURE_STATE(stmt);
+      mozStorageStatementScoper scope(stmt);
+
+      rv = stmt->BindUTF8StringByName("scope"_ns, mOrigin + "*"_ns);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = stmt->Execute();
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      // No need to selectively clear mOriginsHavingData here.  That hashtable
+      // only prevents preload for scopes with no data.  Leaving a false record
+      // in it has a negligible effect on performance.
+      break;
+    }
+
+    case opClearMatchingOriginAttributes: {
+      MOZ_ASSERT(!NS_IsMainThread());
+
+      // Register the ORIGIN_ATTRS_PATTERN_MATCH function, initialized with the
+      // pattern
+      nsCOMPtr<mozIStorageFunction> patternMatchFunction(
+          new OriginAttrsPatternMatchSQLFunction(mOriginPattern));
+
+      rv = aThread->mWorkerConnection->CreateFunction(
+          "ORIGIN_ATTRS_PATTERN_MATCH"_ns, 1, patternMatchFunction);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      nsCOMPtr<mozIStorageStatement> stmt =
+          aThread->mWorkerStatements.GetCachedStatement(
+              "DELETE FROM webappsstore2"
+              " WHERE ORIGIN_ATTRS_PATTERN_MATCH(originAttributes)");
+
+      if (stmt) {
+        mozStorageStatementScoper scope(stmt);
+        rv = stmt->Execute();
+      } else {
+        rv = NS_ERROR_UNEXPECTED;
+      }
+
+      // Always remove the function
+      aThread->mWorkerConnection->RemoveFunction(
+          "ORIGIN_ATTRS_PATTERN_MATCH"_ns);
+
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      // No need to selectively clear mOriginsHavingData here.  That hashtable
+      // only prevents preload for scopes with no data.  Leaving a false record
+      // in it has a negligible effect on performance.
+      break;
+    }
+
+    default:
+      NS_ERROR("Unknown task type");
+      break;
+  }
+
+  return NS_OK;
+}
+
+void StorageDBThread::DBOperation::Finalize(nsresult aRv) {
+  switch (mType) {
+    case opPreloadUrgent:
+    case opPreload:
+      if (NS_FAILED(aRv)) {
+        // When we are here, something failed when loading from the database.
+        // Notify that the storage is loaded to prevent deadlock of the main
+        // thread, even though it is actually empty or incomplete.
+        NS_WARNING("Failed to preload localStorage");
+      }
+
+      mCache->LoadDone(aRv);
+      break;
+
+    case opGetUsage:
+      if (NS_FAILED(aRv)) {
+        mUsage->LoadUsage(0);
+      }
+
+      break;
+
+    default:
+      if (NS_FAILED(aRv)) {
+        NS_WARNING(
+            "localStorage update/clear operation failed,"
+            " data may not persist or clean up");
+      }
+
+      break;
+  }
+}
+
+// StorageDBThread::PendingOperations
+
+StorageDBThread::PendingOperations::PendingOperations()
+    : mFlushFailureCount(0) {}
+
+bool StorageDBThread::PendingOperations::HasTasks() const {
+  return !!mUpdates.Count() || !!mClears.Count();
+}
+
+namespace {
+
+bool OriginPatternMatches(const nsACString& aOriginSuffix,
+                          const OriginAttributesPattern& aPattern) {
+  OriginAttributes oa;
+  DebugOnly<bool> rv = oa.PopulateFromSuffix(aOriginSuffix);
+  MOZ_ASSERT(rv);
+  return aPattern.Matches(oa);
+}
+
+}  // namespace
+
+bool StorageDBThread::PendingOperations::CheckForCoalesceOpportunity(
+    DBOperation* aNewOp, DBOperation::OperationType aPendingType,
+    DBOperation::OperationType aNewType) {
+  if (aNewOp->Type() != aNewType) {
+    return false;
+  }
+
+  StorageDBThread::DBOperation* pendingTask;
+  if (!mUpdates.Get(aNewOp->Target(), &pendingTask)) {
+    return false;
+  }
+
+  if (pendingTask->Type() != aPendingType) {
+    return false;
+  }
+
+  return true;
+}
+
+void StorageDBThread::PendingOperations::Add(
+    UniquePtr<StorageDBThread::DBOperation> aOperation) {
+  // Optimize: when a key to remove has never been written to disk
+  // just bypass this operation.  A key is new when an operation scheduled
+  // to write it to the database is of type opAddItem.
+  if (CheckForCoalesceOpportunity(aOperation.get(), DBOperation::opAddItem,
+                                  DBOperation::opRemoveItem)) {
+    mUpdates.Remove(aOperation->Target());
+    return;
+  }
+
+  // Optimize: when changing a key that is new and has never been
+  // written to disk, keep type of the operation to store it at opAddItem.
+  // This allows optimization to just forget adding a new key when
+  // it is removed from the storage before flush.
+  if (CheckForCoalesceOpportunity(aOperation.get(), DBOperation::opAddItem,
+                                  DBOperation::opUpdateItem)) {
+    aOperation->mType = DBOperation::opAddItem;
+  }
+
+  // Optimize: to prevent lose of remove operation on a key when doing
+  // remove/set/remove on a previously existing key we have to change
+  // opAddItem to opUpdateItem on the new operation when there is opRemoveItem
+  // pending for the key.
+  if (CheckForCoalesceOpportunity(aOperation.get(), DBOperation::opRemoveItem,
+                                  DBOperation::opAddItem)) {
+    aOperation->mType = DBOperation::opUpdateItem;
+  }
+
+  switch (aOperation->Type()) {
+      // Operations on single keys
+
+    case DBOperation::opAddItem:
+    case DBOperation::opUpdateItem:
+    case DBOperation::opRemoveItem:
+      // Override any existing operation for the target (=scope+key).
+      mUpdates.InsertOrUpdate(aOperation->Target(), std::move(aOperation));
+      break;
+
+      // Clear operations
+
+    case DBOperation::opClear:
+    case DBOperation::opClearMatchingOrigin:
+    case DBOperation::opClearMatchingOriginAttributes:
+      // Drop all update (insert/remove) operations for equivavelent or matching
+      // scope.  We do this as an optimization as well as a must based on the
+      // logic, if we would not delete the update tasks, changes would have been
+      // stored to the database after clear operations have been executed.
+      for (auto iter = mUpdates.Iter(); !iter.Done(); iter.Next()) {
+        const auto& pendingTask = iter.Data();
+
+        if (aOperation->Type() == DBOperation::opClear &&
+            (pendingTask->OriginNoSuffix() != aOperation->OriginNoSuffix() ||
+             pendingTask->OriginSuffix() != aOperation->OriginSuffix())) {
+          continue;
+        }
+
+        if (aOperation->Type() == DBOperation::opClearMatchingOrigin &&
+            !StringBeginsWith(pendingTask->OriginNoSuffix(),
+                              aOperation->Origin())) {
+          continue;
+        }
+
+        if (aOperation->Type() ==
+                DBOperation::opClearMatchingOriginAttributes &&
+            !OriginPatternMatches(pendingTask->OriginSuffix(),
+                                  aOperation->OriginPattern())) {
+          continue;
+        }
+
+        iter.Remove();
+      }
+
+      mClears.InsertOrUpdate(aOperation->Target(), std::move(aOperation));
+      break;
+
+    case DBOperation::opClearAll:
+      // Drop simply everything, this is a super-operation.
+      mUpdates.Clear();
+      mClears.Clear();
+      mClears.InsertOrUpdate(aOperation->Target(), std::move(aOperation));
+      break;
+
+    default:
+      MOZ_ASSERT(false);
+      break;
+  }
+}
+
+bool StorageDBThread::PendingOperations::Prepare() {
+  // Called under the lock
+
+  // First collect clear operations and then updates, we can
+  // do this since whenever a clear operation for a scope is
+  // scheduled, we drop all updates matching that scope. So,
+  // all scope-related update operations we have here now were
+  // scheduled after the clear operations.
+  for (auto iter = mClears.Iter(); !iter.Done(); iter.Next()) {
+    mExecList.AppendElement(std::move(iter.Data()));
+  }
+  mClears.Clear();
+
+  for (auto iter = mUpdates.Iter(); !iter.Done(); iter.Next()) {
+    mExecList.AppendElement(std::move(iter.Data()));
+  }
+  mUpdates.Clear();
+
+  return !!mExecList.Length();
+}
+
+nsresult StorageDBThread::PendingOperations::Execute(StorageDBThread* aThread) {
+  // Called outside the lock
+
+  mozStorageTransaction transaction(aThread->mWorkerConnection, false);
+
+  nsresult rv = transaction.Start();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  for (uint32_t i = 0; i < mExecList.Length(); ++i) {
+    const auto& task = mExecList[i];
+    rv = task->Perform(aThread);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+  }
+
+  rv = transaction.Commit();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+bool StorageDBThread::PendingOperations::Finalize(nsresult aRv) {
+  // Called under the lock
+
+  // The list is kept on a failure to retry it
+  if (NS_FAILED(aRv)) {
+    // XXX Followup: we may try to reopen the database and flush these
+    // pending tasks, however testing showed that even though I/O is actually
+    // broken some amount of operations is left in sqlite+system buffers and
+    // seems like successfully flushed to disk.
+    // Tested by removing a flash card and disconnecting from network while
+    // using a network drive on Windows system.
+    NS_WARNING("Flush operation on localStorage database failed");
+
+    ++mFlushFailureCount;
+
+    return mFlushFailureCount >= 5;
+  }
+
+  mFlushFailureCount = 0;
+  mExecList.Clear();
+  return true;
+}
+
+namespace {
+
+bool FindPendingClearForOrigin(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix,
+    StorageDBThread::DBOperation* aPendingOperation) {
+  if (aPendingOperation->Type() == StorageDBThread::DBOperation::opClearAll) {
+    return true;
+  }
+
+  if (aPendingOperation->Type() == StorageDBThread::DBOperation::opClear &&
+      aOriginNoSuffix == aPendingOperation->OriginNoSuffix() &&
+      aOriginSuffix == aPendingOperation->OriginSuffix()) {
+    return true;
+  }
+
+  if (aPendingOperation->Type() ==
+          StorageDBThread::DBOperation::opClearMatchingOrigin &&
+      StringBeginsWith(aOriginNoSuffix, aPendingOperation->Origin())) {
+    return true;
+  }
+
+  if (aPendingOperation->Type() ==
+          StorageDBThread::DBOperation::opClearMatchingOriginAttributes &&
+      OriginPatternMatches(aOriginSuffix, aPendingOperation->OriginPattern())) {
+    return true;
+  }
+
+  return false;
+}
+
+}  // namespace
+
+bool StorageDBThread::PendingOperations::IsOriginClearPending(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix) const {
+  // Called under the lock
+
+  for (const auto& clear : mClears.Values()) {
+    if (FindPendingClearForOrigin(aOriginSuffix, aOriginNoSuffix,
+                                  clear.get())) {
+      return true;
+    }
+  }
+
+  for (uint32_t i = 0; i < mExecList.Length(); ++i) {
+    if (FindPendingClearForOrigin(aOriginSuffix, aOriginNoSuffix,
+                                  mExecList[i].get())) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+namespace {
+
+bool FindPendingUpdateForOrigin(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix,
+    StorageDBThread::DBOperation* aPendingOperation) {
+  if ((aPendingOperation->Type() == StorageDBThread::DBOperation::opAddItem ||
+       aPendingOperation->Type() ==
+           StorageDBThread::DBOperation::opUpdateItem ||
+       aPendingOperation->Type() ==
+           StorageDBThread::DBOperation::opRemoveItem) &&
+      aOriginNoSuffix == aPendingOperation->OriginNoSuffix() &&
+      aOriginSuffix == aPendingOperation->OriginSuffix()) {
+    return true;
+  }
+
+  return false;
+}
+
+}  // namespace
+
+bool StorageDBThread::PendingOperations::IsOriginUpdatePending(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix) const {
+  // Called under the lock
+
+  for (const auto& update : mUpdates.Values()) {
+    if (FindPendingUpdateForOrigin(aOriginSuffix, aOriginNoSuffix,
+                                   update.get())) {
+      return true;
+    }
+  }
+
+  for (uint32_t i = 0; i < mExecList.Length(); ++i) {
+    if (FindPendingUpdateForOrigin(aOriginSuffix, aOriginNoSuffix,
+                                   mExecList[i].get())) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+nsresult StorageDBThread::InitHelper::SyncDispatchAndReturnProfilePath(
+    nsAString& aProfilePath) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  MOZ_ALWAYS_SUCCEEDS(NS_DispatchToMainThread(this));
+
+  mozilla::MutexAutoLock autolock(mMutex);
+  while (mWaiting) {
+    mCondVar.Wait();
+  }
+
+  if (NS_WARN_IF(NS_FAILED(mMainThreadResultCode))) {
+    return mMainThreadResultCode;
+  }
+
+  aProfilePath = mProfilePath;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+StorageDBThread::InitHelper::Run() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  nsresult rv = GetProfilePath(mProfilePath);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    mMainThreadResultCode = rv;
+  }
+
+  mozilla::MutexAutoLock lock(mMutex);
+  MOZ_ASSERT(mWaiting);
+
+  mWaiting = false;
+  mCondVar.Notify();
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+StorageDBThread::NoteBackgroundThreadRunnable::Run() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  StorageObserver* observer = StorageObserver::Self();
+  MOZ_ASSERT(observer);
+
+  observer->NoteBackgroundThread(mPrivateBrowsingId, mOwningThread);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+StorageDBThread::ShutdownRunnable::Run() {
+  if (NS_IsMainThread()) {
+    mDone = true;
+
+    return NS_OK;
+  }
+
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_RELEASE_ASSERT(mPrivateBrowsingId < kPrivateBrowsingIdCount);
+
+  StorageDBThread*& storageThread = sStorageThread[mPrivateBrowsingId];
+  if (storageThread) {
+    sStorageThreadDown[mPrivateBrowsingId] = true;
+
+    storageThread->Shutdown();
+
+    delete storageThread;
+    storageThread = nullptr;
+  }
+
+  MOZ_ALWAYS_SUCCEEDS(NS_DispatchToMainThread(this));
+
+  return NS_OK;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/storage/StorageDBThread.h b/dom/storage/StorageDBThread.h
new file mode 100644
index 0000000000..7708de5a97
--- /dev/null
+++ b/dom/storage/StorageDBThread.h
@@ -0,0 +1,493 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_dom_StorageDBThread_h
+#define mozilla_dom_StorageDBThread_h
+
+#include "prthread.h"
+#include "prinrval.h"
+#include "nsTArray.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/Monitor.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/OriginAttributes.h"
+#include "mozilla/storage/StatementCache.h"
+#include "mozilla/TimeStamp.h"
+#include "mozilla/UniquePtr.h"
+#include "nsString.h"
+#include "nsCOMPtr.h"
+#include "nsClassHashtable.h"
+#include "nsIFile.h"
+#include "nsIThreadInternal.h"
+#include "nsThreadUtils.h"
+#include "nsTHashSet.h"
+
+class mozIStorageConnection;
+
+namespace mozilla::dom {
+
+class LocalStorageCacheBridge;
+class StorageUsageBridge;
+class StorageUsage;
+
+using StatementCache = mozilla::storage::StatementCache<mozIStorageStatement>;
+
+// XXX Fix me!
+//     1. Move comments to StorageDBThread/StorageDBChild.
+//     2. Devirtualize relevant methods in StorageDBThread/StorageDBChild.
+//     3. Remove relevant methods in StorageDBThread/StorageDBChild that are
+//        unused.
+//     4. Remove this class completely.
+//
+//     See bug 1387636 for more details.
+#if 0
+// Interface used by the cache to post operations to the asynchronous
+// database thread or process.
+class StorageDBBridge
+{
+public:
+  StorageDBBridge();
+  virtual ~StorageDBBridge() {}
+
+  // Ensures the database engine is started
+  virtual nsresult Init() = 0;
+
+  // Releases the database and disallows its usage
+  virtual nsresult Shutdown() = 0;
+
+  // Asynchronously fills the cache with data from the database for first use.
+  // When |aPriority| is true, the preload operation is scheduled as the first
+  // one.  This method is responsible to keep hard reference to the cache for
+  // the time of the preload or, when preload cannot be performed, call
+  // LoadDone() immediately.
+  virtual void AsyncPreload(LocalStorageCacheBridge* aCache,
+                            bool aPriority = false) = 0;
+
+  // Asynchronously fill the |usage| object with actual usage of data by its
+  // scope.  The scope is eTLD+1 tops, never deeper subdomains.
+  virtual void AsyncGetUsage(StorageUsageBridge* aUsage) = 0;
+
+  // Synchronously fills the cache, when |aForceSync| is false and cache already
+  // got some data before, the method waits for the running preload to finish
+  virtual void SyncPreload(LocalStorageCacheBridge* aCache,
+                           bool aForceSync = false) = 0;
+
+  // Called when an existing key is modified in the storage, schedules update to
+  // the database
+  virtual nsresult AsyncAddItem(LocalStorageCacheBridge* aCache,
+                                const nsAString& aKey,
+                                const nsAString& aValue) = 0;
+
+  // Called when an existing key is modified in the storage, schedules update to
+  // the database
+  virtual nsresult AsyncUpdateItem(LocalStorageCacheBridge* aCache,
+                                   const nsAString& aKey,
+                                   const nsAString& aValue) = 0;
+
+  // Called when an item is removed from the storage, schedules delete of the
+  // key
+  virtual nsresult AsyncRemoveItem(LocalStorageCacheBridge* aCache,
+                                   const nsAString& aKey) = 0;
+
+  // Called when the whole storage is cleared by the DOM API, schedules delete
+  // of the scope
+  virtual nsresult AsyncClear(LocalStorageCacheBridge* aCache) = 0;
+
+  // Called when chrome deletes e.g. cookies, schedules delete of the whole
+  // database
+  virtual void AsyncClearAll() = 0;
+
+  // Called when only a domain and its subdomains is about to clear
+  virtual void AsyncClearMatchingOrigin(const nsACString& aOriginNoSuffix) = 0;
+
+  // Called when data matching an origin pattern have to be cleared
+  virtual void AsyncClearMatchingOriginAttributes(const OriginAttributesPattern& aPattern) = 0;
+
+  // Forces scheduled DB operations to be early flushed to the disk
+  virtual void AsyncFlush() = 0;
+
+  // Check whether the scope has any data stored on disk and is thus allowed to
+  // preload
+  virtual bool ShouldPreloadOrigin(const nsACString& aOriginNoSuffix) = 0;
+};
+#endif
+
+// The implementation of the the database engine, this directly works
+// with the sqlite or any other db API we are based on
+// This class is resposible for collecting and processing asynchronous
+// DB operations over caches (LocalStorageCache) communicating though
+// LocalStorageCacheBridge interface class
+class StorageDBThread final {
+ public:
+  class PendingOperations;
+
+  // Representation of a singe database task, like adding and removing keys,
+  // (pre)loading the whole origin data, cleaning.
+  class DBOperation {
+   public:
+    enum OperationType {
+      // Only operation that reads data from the database
+      opPreload,
+      // The same as opPreload, just executed with highest priority
+      opPreloadUrgent,
+
+      // Load usage of a scope
+      opGetUsage,
+
+      // Operations invoked by the DOM content API
+      opAddItem,
+      opUpdateItem,
+      opRemoveItem,
+      // Clears a specific single origin data
+      opClear,
+
+      // Operations invoked by chrome
+
+      // Clear all the data stored in the database, for all scopes, no
+      // exceptions
+      opClearAll,
+      // Clear data under a domain and all its subdomains regardless
+      // OriginAttributes value
+      opClearMatchingOrigin,
+      // Clear all data matching an OriginAttributesPattern regardless a domain
+      opClearMatchingOriginAttributes,
+    };
+
+    explicit DBOperation(const OperationType aType,
+                         LocalStorageCacheBridge* aCache = nullptr,
+                         const nsAString& aKey = u""_ns,
+                         const nsAString& aValue = u""_ns);
+    DBOperation(const OperationType aType, StorageUsageBridge* aUsage);
+    DBOperation(const OperationType aType, const nsACString& aOriginNoSuffix);
+    DBOperation(const OperationType aType,
+                const OriginAttributesPattern& aOriginNoSuffix);
+    ~DBOperation();
+
+    // Executes the operation, doesn't necessarity have to be called on the I/O
+    // thread
+    void PerformAndFinalize(StorageDBThread* aThread);
+
+    // Finalize the operation, i.e. do any internal cleanup and finish calls
+    void Finalize(nsresult aRv);
+
+    // The operation type
+    OperationType Type() const { return mType; }
+
+    // The origin in the database usage format (reversed)
+    const nsCString OriginNoSuffix() const;
+
+    // The origin attributes suffix
+    const nsCString OriginSuffix() const;
+
+    // |origin suffix + origin key| the operation is working with or a scope
+    // pattern to delete with simple SQL's "LIKE %" from the database.
+    const nsCString Origin() const;
+
+    // |origin suffix + origin key + key| the operation is working with
+    const nsCString Target() const;
+
+    // Pattern to delete matching data with this op
+    const OriginAttributesPattern& OriginPattern() const {
+      return mOriginPattern;
+    }
+
+   private:
+    // The operation implementation body
+    nsresult Perform(StorageDBThread* aThread);
+
+    friend class PendingOperations;
+    OperationType mType;
+    RefPtr<LocalStorageCacheBridge> mCache;
+    RefPtr<StorageUsageBridge> mUsage;
+    nsString const mKey;
+    nsString const mValue;
+    nsCString const mOrigin;
+    OriginAttributesPattern const mOriginPattern;
+  };
+
+  // Encapsulation of collective and coalescing logic for all pending operations
+  // except preloads that are handled separately as priority operations
+  class PendingOperations {
+   public:
+    PendingOperations();
+
+    // Method responsible for coalescing redundant update operations with the
+    // same |Target()| or clear operations with the same or matching |Origin()|
+    void Add(UniquePtr<DBOperation> aOperation);
+
+    // True when there are some scheduled operations to flush on disk
+    bool HasTasks() const;
+
+    // Moves collected operations to a local flat list to allow execution of the
+    // operation list out of the thread lock
+    bool Prepare();
+
+    // Executes the previously |Prepared()'ed| list of operations, returns
+    // result, but doesn't handle it in any way in case of a failure
+    nsresult Execute(StorageDBThread* aThread);
+
+    // Finalizes the pending operation list, returns false when too many
+    // operations failed to flush what indicates a long standing issue with the
+    // database access.
+    bool Finalize(nsresult aRv);
+
+    // true when a clear that deletes the given origin attr pattern and/or
+    // origin key is among the pending operations; when a preload for that scope
+    // is being scheduled, it must be finished right away
+    bool IsOriginClearPending(const nsACString& aOriginSuffix,
+                              const nsACString& aOriginNoSuffix) const;
+
+    // Checks whether there is a pending update operation for this scope.
+    bool IsOriginUpdatePending(const nsACString& aOriginSuffix,
+                               const nsACString& aOriginNoSuffix) const;
+
+   private:
+    // Returns true iff new operation is of type newType and there is a pending
+    // operation of type pendingType for the same key (target).
+    bool CheckForCoalesceOpportunity(DBOperation* aNewOp,
+                                     DBOperation::OperationType aPendingType,
+                                     DBOperation::OperationType aNewType);
+
+    // List of all clearing operations, executed first
+    nsClassHashtable<nsCStringHashKey, DBOperation> mClears;
+
+    // List of all update/insert operations, executed as second
+    nsClassHashtable<nsCStringHashKey, DBOperation> mUpdates;
+
+    // Collection of all tasks, valid only between Prepare() and Execute()
+    nsTArray<UniquePtr<DBOperation> > mExecList;
+
+    // Number of failing flush attempts
+    uint32_t mFlushFailureCount;
+  };
+
+  class ThreadObserver final : public nsIThreadObserver {
+    NS_DECL_THREADSAFE_ISUPPORTS
+    NS_DECL_NSITHREADOBSERVER
+
+    ThreadObserver()
+        : mHasPendingEvents(false), mMonitor("StorageThreadMonitor") {}
+
+    bool HasPendingEvents() {
+      mMonitor.AssertCurrentThreadOwns();
+      return mHasPendingEvents;
+    }
+    void ClearPendingEvents() {
+      mMonitor.AssertCurrentThreadOwns();
+      mHasPendingEvents = false;
+    }
+    Monitor& GetMonitor() { return mMonitor; }
+
+   private:
+    virtual ~ThreadObserver() = default;
+    bool mHasPendingEvents;
+    // The monitor we drive the thread with
+    Monitor mMonitor MOZ_UNANNOTATED;
+  };
+
+  class InitHelper;
+
+  class NoteBackgroundThreadRunnable;
+
+  class ShutdownRunnable : public Runnable {
+    // Expected to be only 0 or 1.
+    const uint32_t mPrivateBrowsingId;
+    // Only touched on the main thread.
+    bool& mDone;
+
+   public:
+    explicit ShutdownRunnable(const uint32_t aPrivateBrowsingId, bool& aDone)
+        : Runnable("dom::StorageDBThread::ShutdownRunnable"),
+          mPrivateBrowsingId(aPrivateBrowsingId),
+          mDone(aDone) {
+      MOZ_ASSERT(NS_IsMainThread());
+    }
+
+   private:
+    ~ShutdownRunnable() = default;
+
+    NS_DECL_NSIRUNNABLE
+  };
+
+ public:
+  explicit StorageDBThread(uint32_t aPrivateBrowsingId);
+  virtual ~StorageDBThread() = default;
+
+  static StorageDBThread* Get(uint32_t aPrivateBrowsingId);
+
+  static StorageDBThread* GetOrCreate(const nsString& aProfilePath,
+                                      uint32_t aPrivateBrowsingId);
+
+  static nsresult GetProfilePath(nsString& aProfilePath);
+
+  virtual nsresult Init(const nsString& aProfilePath);
+
+  // Flushes all uncommited data and stops the I/O thread.
+  virtual nsresult Shutdown();
+
+  virtual void AsyncPreload(LocalStorageCacheBridge* aCache,
+                            bool aPriority = false) {
+    InsertDBOp(MakeUnique<DBOperation>(
+        aPriority ? DBOperation::opPreloadUrgent : DBOperation::opPreload,
+        aCache));
+  }
+
+  virtual void SyncPreload(LocalStorageCacheBridge* aCache,
+                           bool aForce = false);
+
+  virtual void AsyncGetUsage(StorageUsageBridge* aUsage) {
+    InsertDBOp(MakeUnique<DBOperation>(DBOperation::opGetUsage, aUsage));
+  }
+
+  virtual nsresult AsyncAddItem(LocalStorageCacheBridge* aCache,
+                                const nsAString& aKey,
+                                const nsAString& aValue) {
+    return InsertDBOp(
+        MakeUnique<DBOperation>(DBOperation::opAddItem, aCache, aKey, aValue));
+  }
+
+  virtual nsresult AsyncUpdateItem(LocalStorageCacheBridge* aCache,
+                                   const nsAString& aKey,
+                                   const nsAString& aValue) {
+    return InsertDBOp(MakeUnique<DBOperation>(DBOperation::opUpdateItem, aCache,
+                                              aKey, aValue));
+  }
+
+  virtual nsresult AsyncRemoveItem(LocalStorageCacheBridge* aCache,
+                                   const nsAString& aKey) {
+    return InsertDBOp(
+        MakeUnique<DBOperation>(DBOperation::opRemoveItem, aCache, aKey));
+  }
+
+  virtual nsresult AsyncClear(LocalStorageCacheBridge* aCache) {
+    return InsertDBOp(MakeUnique<DBOperation>(DBOperation::opClear, aCache));
+  }
+
+  virtual void AsyncClearAll() {
+    InsertDBOp(MakeUnique<DBOperation>(DBOperation::opClearAll));
+  }
+
+  virtual void AsyncClearMatchingOrigin(const nsACString& aOriginNoSuffix) {
+    InsertDBOp(MakeUnique<DBOperation>(DBOperation::opClearMatchingOrigin,
+                                       aOriginNoSuffix));
+  }
+
+  virtual void AsyncClearMatchingOriginAttributes(
+      const OriginAttributesPattern& aPattern) {
+    InsertDBOp(MakeUnique<DBOperation>(
+        DBOperation::opClearMatchingOriginAttributes, aPattern));
+  }
+
+  virtual void AsyncFlush();
+
+  virtual bool ShouldPreloadOrigin(const nsACString& aOrigin);
+
+  // Get the complete list of scopes having data.
+  void GetOriginsHavingData(nsTArray<nsCString>* aOrigins);
+
+ private:
+  nsCOMPtr<nsIFile> mDatabaseFile;
+  PRThread* mThread;
+
+  // Used to observe runnables dispatched to our thread and to monitor it.
+  RefPtr<ThreadObserver> mThreadObserver;
+
+  // Flag to stop, protected by the monitor returned by
+  // mThreadObserver->GetMonitor().
+  bool mStopIOThread;
+
+  // Whether WAL is enabled
+  bool mWALModeEnabled;
+
+  // Whether DB has already been open, avoid races between main thread reads
+  // and pending DB init in the background I/O thread
+  Atomic<bool, ReleaseAcquire> mDBReady;
+
+  // State of the database initiation
+  nsresult mStatus;
+
+  // List of origins (including origin attributes suffix) having data, for
+  // optimization purposes only
+  nsTHashSet<nsCString> mOriginsHavingData;
+
+  // Connection used by the worker thread for all read and write ops
+  nsCOMPtr<mozIStorageConnection> mWorkerConnection;
+
+  // Connection used only on the main thread for sync read operations
+  nsCOMPtr<mozIStorageConnection> mReaderConnection;
+
+  StatementCache mWorkerStatements;
+  StatementCache mReaderStatements;
+
+  // Time the first pending operation has been added to the pending operations
+  // list
+  TimeStamp mDirtyEpoch;
+
+  // Flag to force immediate flush of all pending operations
+  bool mFlushImmediately;
+
+  // List of preloading operations, in chronological or priority order.
+  // Executed prioritly over pending update operations.
+  nsTArray<DBOperation*> mPreloads;
+
+  // Collector of pending update operations
+  PendingOperations mPendingTasks;
+
+  // Expected to be only 0 or 1.
+  const uint32_t mPrivateBrowsingId;
+
+  // Counter of calls for thread priority rising.
+  int32_t mPriorityCounter;
+
+  // Helper to direct an operation to one of the arrays above;
+  // also checks IsOriginClearPending for preloads
+  nsresult InsertDBOp(UniquePtr<DBOperation> aOperation);
+
+  // Opens the database, first thing we do after start of the thread.
+  nsresult OpenDatabaseConnection();
+  nsresult OpenAndUpdateDatabase();
+  nsresult InitDatabase();
+  nsresult ShutdownDatabase();
+
+  // Tries to establish WAL mode
+  nsresult SetJournalMode(bool aIsWal);
+  nsresult TryJournalMode();
+
+  // Sets the threshold for auto-checkpointing the WAL.
+  nsresult ConfigureWALBehavior();
+
+  void SetHigherPriority();
+  void SetDefaultPriority();
+
+  // Ensures we flush pending tasks in some reasonble time
+  void ScheduleFlush();
+
+  // Called when flush of pending tasks is being executed
+  void UnscheduleFlush();
+
+  // This method is used for two purposes:
+  // 1. as a value passed to monitor.Wait() method
+  // 2. as in indicator that flush has to be performed
+  //
+  // Return:
+  // - TimeDuration::Forever() when no pending tasks are scheduled
+  // - Non-zero TimeDuration when tasks have been scheduled, but it
+  //   is still not time to perform the flush ; it is actual time to
+  //   wait until the flush has to happen.
+  // - 0 TimeDuration when it is time to do the flush
+  TimeDuration TimeUntilFlush();
+
+  // Notifies to the main thread that flush has completed
+  void NotifyFlushCompletion();
+
+  // Thread loop
+  static void ThreadFunc(void* aArg);
+  void ThreadFunc();
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_StorageDBThread_h
diff --git a/dom/storage/StorageDBUpdater.cpp b/dom/storage/StorageDBUpdater.cpp
new file mode 100644
index 0000000000..7dec6425e2
--- /dev/null
+++ b/dom/storage/StorageDBUpdater.cpp
@@ -0,0 +1,524 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "LocalStorageManager.h"
+#include "StorageUtils.h"
+
+#include "mozIStorageBindingParams.h"
+#include "mozIStorageValueArray.h"
+#include "mozIStorageFunction.h"
+#include "mozilla/BasePrincipal.h"
+#include "nsVariant.h"
+#include "mozilla/Tokenizer.h"
+#include "mozIStorageConnection.h"
+#include "mozStorageHelper.h"
+
+// Current version of the database schema
+#define CURRENT_SCHEMA_VERSION 2
+
+namespace mozilla::dom {
+
+using namespace StorageUtils;
+
+namespace {
+
+class nsReverseStringSQLFunction final : public mozIStorageFunction {
+  ~nsReverseStringSQLFunction() = default;
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_MOZISTORAGEFUNCTION
+};
+
+NS_IMPL_ISUPPORTS(nsReverseStringSQLFunction, mozIStorageFunction)
+
+NS_IMETHODIMP
+nsReverseStringSQLFunction::OnFunctionCall(
+    mozIStorageValueArray* aFunctionArguments, nsIVariant** aResult) {
+  nsresult rv;
+
+  nsAutoCString stringToReverse;
+  rv = aFunctionArguments->GetUTF8String(0, stringToReverse);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsAutoCString result;
+  ReverseString(stringToReverse, result);
+
+  RefPtr<nsVariant> outVar(new nsVariant());
+  rv = outVar->SetAsAUTF8String(result);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  outVar.forget(aResult);
+  return NS_OK;
+}
+
+// "scope" to "origin attributes suffix" and "origin key" convertor
+
+class ExtractOriginData : protected mozilla::Tokenizer {
+ public:
+  ExtractOriginData(const nsACString& scope, nsACString& suffix,
+                    nsACString& origin)
+      : mozilla::Tokenizer(scope) {
+    using mozilla::OriginAttributes;
+
+    // Parse optional appId:isInIsolatedMozBrowserElement: string, in case
+    // we don't find it, the scope is our new origin key and suffix
+    // is empty.
+    suffix.Truncate();
+    origin.Assign(scope);
+
+    // Bail out if it isn't appId.
+    // AppId doesn't exist any more but we could have old storage data...
+    uint32_t appId;
+    if (!ReadInteger(&appId)) {
+      return;
+    }
+
+    // Should be followed by a colon.
+    if (!CheckChar(':')) {
+      return;
+    }
+
+    // Bail out if it isn't 'isolatedBrowserFlag'.
+    nsDependentCSubstring isolatedBrowserFlag;
+    if (!ReadWord(isolatedBrowserFlag)) {
+      return;
+    }
+
+    bool inIsolatedMozBrowser = isolatedBrowserFlag == "t";
+    bool notInIsolatedBrowser = isolatedBrowserFlag == "f";
+    if (!inIsolatedMozBrowser && !notInIsolatedBrowser) {
+      return;
+    }
+
+    // Should be followed by a colon.
+    if (!CheckChar(':')) {
+      return;
+    }
+
+    // OK, we have found appId and inIsolatedMozBrowser flag, create the suffix
+    // from it and take the rest as the origin key.
+
+    // If the profile went through schema 1 -> schema 0 -> schema 1 switching
+    // we may have stored the full attributes origin suffix when there were
+    // more than just appId and inIsolatedMozBrowser set on storage principal's
+    // OriginAttributes.
+    //
+    // To preserve full uniqueness we store this suffix to the scope key.
+    // Schema 0 code will just ignore it while keeping the scoping unique.
+    //
+    // The whole scope string is in one of the following forms (when we are
+    // here):
+    //
+    // "1001:f:^appId=1001&inBrowser=false&addonId=101:gro.allizom.rxd.:https:443"
+    // "1001:f:gro.allizom.rxd.:https:443"
+    //         |
+    //         +- the parser cursor position.
+    //
+    // If there is '^', the full origin attributes suffix follows.  We search
+    // for ':' since it is the delimiter used in the scope string and is never
+    // contained in the origin attributes suffix.  Remaining string after
+    // the comma is the reversed-domain+schema+port tuple.
+    Record();
+    if (CheckChar('^')) {
+      Token t;
+      while (Next(t)) {
+        if (t.Equals(Token::Char(':'))) {
+          Claim(suffix);
+          break;
+        }
+      }
+    } else {
+      OriginAttributes attrs(inIsolatedMozBrowser);
+      attrs.CreateSuffix(suffix);
+    }
+
+    // Consume the rest of the input as "origin".
+    origin.Assign(Substring(mCursor, mEnd));
+  }
+};
+
+class GetOriginParticular final : public mozIStorageFunction {
+ public:
+  enum EParticular { ORIGIN_ATTRIBUTES_SUFFIX, ORIGIN_KEY };
+
+  explicit GetOriginParticular(EParticular aParticular)
+      : mParticular(aParticular) {}
+
+ private:
+  GetOriginParticular() = delete;
+  ~GetOriginParticular() = default;
+
+  EParticular mParticular;
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_MOZISTORAGEFUNCTION
+};
+
+NS_IMPL_ISUPPORTS(GetOriginParticular, mozIStorageFunction)
+
+NS_IMETHODIMP
+GetOriginParticular::OnFunctionCall(mozIStorageValueArray* aFunctionArguments,
+                                    nsIVariant** aResult) {
+  nsresult rv;
+
+  nsAutoCString scope;
+  rv = aFunctionArguments->GetUTF8String(0, scope);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsAutoCString suffix, origin;
+  ExtractOriginData extractor(scope, suffix, origin);
+
+  nsCOMPtr<nsIWritableVariant> outVar(new nsVariant());
+
+  switch (mParticular) {
+    case EParticular::ORIGIN_ATTRIBUTES_SUFFIX:
+      rv = outVar->SetAsAUTF8String(suffix);
+      break;
+    case EParticular::ORIGIN_KEY:
+      rv = outVar->SetAsAUTF8String(origin);
+      break;
+  }
+
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  outVar.forget(aResult);
+  return NS_OK;
+}
+
+class StripOriginAddonId final : public mozIStorageFunction {
+ public:
+  explicit StripOriginAddonId() = default;
+
+ private:
+  ~StripOriginAddonId() = default;
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_MOZISTORAGEFUNCTION
+};
+
+NS_IMPL_ISUPPORTS(StripOriginAddonId, mozIStorageFunction)
+
+NS_IMETHODIMP
+StripOriginAddonId::OnFunctionCall(mozIStorageValueArray* aFunctionArguments,
+                                   nsIVariant** aResult) {
+  nsresult rv;
+
+  nsAutoCString suffix;
+  rv = aFunctionArguments->GetUTF8String(0, suffix);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Deserialize and re-serialize to automatically drop any obsolete origin
+  // attributes.
+  OriginAttributes oa;
+  bool ok = oa.PopulateFromSuffix(suffix);
+  NS_ENSURE_TRUE(ok, NS_ERROR_FAILURE);
+
+  nsAutoCString newSuffix;
+  oa.CreateSuffix(newSuffix);
+
+  nsCOMPtr<nsIWritableVariant> outVar = new nsVariant();
+  rv = outVar->SetAsAUTF8String(newSuffix);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  outVar.forget(aResult);
+  return NS_OK;
+}
+
+nsresult CreateSchema1Tables(mozIStorageConnection* aWorkerConnection) {
+  nsresult rv;
+
+  rv = aWorkerConnection->ExecuteSimpleSQL(nsLiteralCString(
+      "CREATE TABLE IF NOT EXISTS webappsstore2 ("
+      "originAttributes TEXT, "
+      "originKey TEXT, "
+      "scope TEXT, "  // Only for schema0 downgrade compatibility
+      "key TEXT, "
+      "value TEXT)"));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = aWorkerConnection->ExecuteSimpleSQL(
+      nsLiteralCString("CREATE UNIQUE INDEX IF NOT EXISTS origin_key_index"
+                       " ON webappsstore2(originAttributes, originKey, key)"));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+nsresult TablesExist(mozIStorageConnection* aWorkerConnection,
+                     bool* aWebappsstore2Exists, bool* aWebappsstoreExists,
+                     bool* aMoz_webappsstoreExists) {
+  nsresult rv =
+      aWorkerConnection->TableExists("webappsstore2"_ns, aWebappsstore2Exists);
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = aWorkerConnection->TableExists("webappsstore"_ns, aWebappsstoreExists);
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = aWorkerConnection->TableExists("moz_webappsstore"_ns,
+                                      aMoz_webappsstoreExists);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+nsresult CreateCurrentSchemaOnEmptyTableInternal(
+    mozIStorageConnection* aWorkerConnection) {
+  nsresult rv = CreateSchema1Tables(aWorkerConnection);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = aWorkerConnection->SetSchemaVersion(CURRENT_SCHEMA_VERSION);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+}  // namespace
+
+namespace StorageDBUpdater {
+
+nsresult CreateCurrentSchema(mozIStorageConnection* aConnection) {
+  mozStorageTransaction transaction(aConnection, false);
+
+  nsresult rv = transaction.Start();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+  {
+    int32_t schemaVer;
+    nsresult rv = aConnection->GetSchemaVersion(&schemaVer);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    MOZ_DIAGNOSTIC_ASSERT(0 == schemaVer);
+
+    bool webappsstore2Exists, webappsstoreExists, moz_webappsstoreExists;
+    rv = TablesExist(aConnection, &webappsstore2Exists, &webappsstoreExists,
+                     &moz_webappsstoreExists);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    MOZ_DIAGNOSTIC_ASSERT(!webappsstore2Exists && !webappsstoreExists &&
+                          !moz_webappsstoreExists);
+  }
+#endif
+
+  rv = CreateCurrentSchemaOnEmptyTableInternal(aConnection);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = transaction.Commit();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+nsresult Update(mozIStorageConnection* aWorkerConnection) {
+  mozStorageTransaction transaction(aWorkerConnection, false);
+
+  nsresult rv = transaction.Start();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  bool doVacuum = false;
+
+  int32_t schemaVer;
+  rv = aWorkerConnection->GetSchemaVersion(&schemaVer);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // downgrade (v0) -> upgrade (v1+) specific code
+  if (schemaVer >= 1) {
+    bool schema0IndexExists;
+    rv = aWorkerConnection->IndexExists("scope_key_index"_ns,
+                                        &schema0IndexExists);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    if (schema0IndexExists) {
+      // If this index exists, the database (already updated to schema >1)
+      // has been run again on schema 0 code.  That recreated that index
+      // and might store some new rows while updating only the 'scope' column.
+      // For such added rows we must fill the new 'origin*' columns correctly
+      // otherwise there would be a data loss.  The safest way to do it is to
+      // simply run the whole update to schema 1 again.
+      schemaVer = 0;
+    }
+  }
+
+  switch (schemaVer) {
+    case 0: {
+      bool webappsstore2Exists, webappsstoreExists, moz_webappsstoreExists;
+      rv = TablesExist(aWorkerConnection, &webappsstore2Exists,
+                       &webappsstoreExists, &moz_webappsstoreExists);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      if (!webappsstore2Exists && !webappsstoreExists &&
+          !moz_webappsstoreExists) {
+        // The database is empty, this is the first start.  Just create the
+        // schema table and break to the next version to update to, i.e. bypass
+        // update from the old version.
+
+        // XXX What does "break to the next version to update to" mean here? It
+        // seems to refer to the 'break' statement below, but that breaks out of
+        // the 'switch' statement and continues with committing the transaction.
+        // Either this is wrong, or the comment above is misleading.
+
+        rv = CreateCurrentSchemaOnEmptyTableInternal(aWorkerConnection);
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        break;
+      }
+
+      doVacuum = true;
+
+      // Ensure Gecko 1.9.1 storage table
+      rv = aWorkerConnection->ExecuteSimpleSQL(
+          nsLiteralCString("CREATE TABLE IF NOT EXISTS webappsstore2 ("
+                           "scope TEXT, "
+                           "key TEXT, "
+                           "value TEXT, "
+                           "secure INTEGER, "
+                           "owner TEXT)"));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = aWorkerConnection->ExecuteSimpleSQL(
+          nsLiteralCString("CREATE UNIQUE INDEX IF NOT EXISTS scope_key_index"
+                           " ON webappsstore2(scope, key)"));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      nsCOMPtr<mozIStorageFunction> function1(new nsReverseStringSQLFunction());
+      NS_ENSURE_TRUE(function1, NS_ERROR_OUT_OF_MEMORY);
+
+      rv = aWorkerConnection->CreateFunction("REVERSESTRING"_ns, 1, function1);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      // Check if there is storage of Gecko 1.9.0 and if so, upgrade that
+      // storage to actual webappsstore2 table and drop the obsolete table.
+      // First process this newer table upgrade to priority potential duplicates
+      // from older storage table.
+      if (webappsstoreExists) {
+        rv = aWorkerConnection->ExecuteSimpleSQL(nsLiteralCString(
+            "INSERT OR IGNORE INTO "
+            "webappsstore2(scope, key, value, secure, owner) "
+            "SELECT REVERSESTRING(domain) || '.:', key, value, secure, owner "
+            "FROM webappsstore"));
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        rv = aWorkerConnection->ExecuteSimpleSQL("DROP TABLE webappsstore"_ns);
+        NS_ENSURE_SUCCESS(rv, rv);
+      }
+
+      // Check if there is storage of Gecko 1.8 and if so, upgrade that storage
+      // to actual webappsstore2 table and drop the obsolete table. Potential
+      // duplicates will be ignored.
+      if (moz_webappsstoreExists) {
+        rv = aWorkerConnection->ExecuteSimpleSQL(nsLiteralCString(
+            "INSERT OR IGNORE INTO "
+            "webappsstore2(scope, key, value, secure, owner) "
+            "SELECT REVERSESTRING(domain) || '.:', key, value, secure, domain "
+            "FROM moz_webappsstore"));
+        NS_ENSURE_SUCCESS(rv, rv);
+
+        rv = aWorkerConnection->ExecuteSimpleSQL(
+            "DROP TABLE moz_webappsstore"_ns);
+        NS_ENSURE_SUCCESS(rv, rv);
+      }
+
+      aWorkerConnection->RemoveFunction("REVERSESTRING"_ns);
+
+      // Update the scoping to match the new implememntation: split to oa suffix
+      // and origin key First rename the old table, we want to remove some
+      // columns no longer needed, but even before that drop all indexes from it
+      // (CREATE IF NOT EXISTS for index on the new table would falsely find the
+      // index!)
+      rv = aWorkerConnection->ExecuteSimpleSQL(nsLiteralCString(
+          "DROP INDEX IF EXISTS webappsstore2.origin_key_index"));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = aWorkerConnection->ExecuteSimpleSQL(nsLiteralCString(
+          "DROP INDEX IF EXISTS webappsstore2.scope_key_index"));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = aWorkerConnection->ExecuteSimpleSQL(nsLiteralCString(
+          "ALTER TABLE webappsstore2 RENAME TO webappsstore2_old"));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      nsCOMPtr<mozIStorageFunction> oaSuffixFunc(new GetOriginParticular(
+          GetOriginParticular::ORIGIN_ATTRIBUTES_SUFFIX));
+      rv = aWorkerConnection->CreateFunction("GET_ORIGIN_SUFFIX"_ns, 1,
+                                             oaSuffixFunc);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      nsCOMPtr<mozIStorageFunction> originKeyFunc(
+          new GetOriginParticular(GetOriginParticular::ORIGIN_KEY));
+      rv = aWorkerConnection->CreateFunction("GET_ORIGIN_KEY"_ns, 1,
+                                             originKeyFunc);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      // Here we ensure this schema tables when we are updating.
+      rv = CreateSchema1Tables(aWorkerConnection);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = aWorkerConnection->ExecuteSimpleSQL(nsLiteralCString(
+          "INSERT OR IGNORE INTO "
+          "webappsstore2 (originAttributes, originKey, scope, key, value) "
+          "SELECT GET_ORIGIN_SUFFIX(scope), GET_ORIGIN_KEY(scope), scope, key, "
+          "value "
+          "FROM webappsstore2_old"));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = aWorkerConnection->ExecuteSimpleSQL(
+          "DROP TABLE webappsstore2_old"_ns);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      aWorkerConnection->RemoveFunction("GET_ORIGIN_SUFFIX"_ns);
+      aWorkerConnection->RemoveFunction("GET_ORIGIN_KEY"_ns);
+
+      rv = aWorkerConnection->SetSchemaVersion(1);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      [[fallthrough]];
+    }
+    case 1: {
+      nsCOMPtr<mozIStorageFunction> oaStripAddonId(new StripOriginAddonId());
+      rv = aWorkerConnection->CreateFunction("STRIP_ADDON_ID"_ns, 1,
+                                             oaStripAddonId);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = aWorkerConnection->ExecuteSimpleSQL(nsLiteralCString(
+          "UPDATE webappsstore2 "
+          "SET originAttributes = STRIP_ADDON_ID(originAttributes) "
+          "WHERE originAttributes LIKE '^%'"));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      aWorkerConnection->RemoveFunction("STRIP_ADDON_ID"_ns);
+
+      rv = aWorkerConnection->SetSchemaVersion(2);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      [[fallthrough]];
+    }
+    case CURRENT_SCHEMA_VERSION:
+      // Ensure the tables and indexes are up.  This is mostly a no-op
+      // in common scenarios.
+      rv = CreateSchema1Tables(aWorkerConnection);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      // Nothing more to do here, this is the current schema version
+      break;
+
+    default:
+      MOZ_ASSERT(false);
+      break;
+  }  // switch
+
+  rv = transaction.Commit();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (doVacuum) {
+    // In some cases this can make the disk file of the database significantly
+    // smaller.  VACUUM cannot be executed inside a transaction.
+    rv = aWorkerConnection->ExecuteSimpleSQL("VACUUM"_ns);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  return NS_OK;
+}
+
+}  // namespace StorageDBUpdater
+}  // namespace mozilla::dom
diff --git a/dom/storage/StorageDBUpdater.h b/dom/storage/StorageDBUpdater.h
new file mode 100644
index 0000000000..6745e7e8cb
--- /dev/null
+++ b/dom/storage/StorageDBUpdater.h
@@ -0,0 +1,20 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_dom_StorageDBUpdater_h
+#define mozilla_dom_StorageDBUpdater_h
+
+namespace mozilla::dom::StorageDBUpdater {
+
+// Must only be called on an empty database.
+nsresult CreateCurrentSchema(mozIStorageConnection* aWorkerConnection);
+
+// XXX Rename to MaybeUpdate or EnsureCurrentSchemaVersion.
+nsresult Update(mozIStorageConnection* aWorkerConnection);
+
+}  // namespace mozilla::dom::StorageDBUpdater
+
+#endif  // mozilla_dom_StorageDBUpdater_h
diff --git a/dom/storage/StorageIPC.cpp b/dom/storage/StorageIPC.cpp
new file mode 100644
index 0000000000..811575f471
--- /dev/null
+++ b/dom/storage/StorageIPC.cpp
@@ -0,0 +1,1598 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "StorageIPC.h"
+
+#include "StorageCommon.h"
+#include "StorageUtils.h"
+#include "LocalStorageManager.h"
+#include "SessionStorageObserver.h"
+#include "SessionStorageManager.h"
+#include "SessionStorageCache.h"
+
+#include "mozilla/dom/LocalStorageCommon.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/ipc/BackgroundParent.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/ipc/PBackgroundParent.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/StoragePrincipalHelper.h"
+#include "mozilla/Unused.h"
+#include "nsCOMPtr.h"
+#include "nsIPrincipal.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla::dom {
+
+namespace {
+
+using LocalStorageCacheParentHashtable =
+    nsClassHashtable<nsCStringHashKey, nsTArray<LocalStorageCacheParent*>>;
+
+StaticAutoPtr<LocalStorageCacheParentHashtable> gLocalStorageCacheParents;
+
+StorageDBChild* sStorageChild[kPrivateBrowsingIdCount] = {nullptr, nullptr};
+
+// False until we shut the storage child down.
+bool sStorageChildDown[kPrivateBrowsingIdCount] = {false, false};
+
+}  // namespace
+
+LocalStorageCacheChild::LocalStorageCacheChild(LocalStorageCache* aCache)
+    : mCache(aCache) {
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aCache);
+  aCache->AssertIsOnOwningThread();
+
+  MOZ_COUNT_CTOR(LocalStorageCacheChild);
+}
+
+LocalStorageCacheChild::~LocalStorageCacheChild() {
+  AssertIsOnOwningThread();
+
+  MOZ_COUNT_DTOR(LocalStorageCacheChild);
+}
+
+void LocalStorageCacheChild::SendDeleteMeInternal() {
+  AssertIsOnOwningThread();
+
+  if (mCache) {
+    mCache->ClearActor();
+    mCache = nullptr;
+
+    MOZ_ALWAYS_TRUE(PBackgroundLocalStorageCacheChild::SendDeleteMe());
+  }
+}
+
+void LocalStorageCacheChild::ActorDestroy(ActorDestroyReason aWhy) {
+  AssertIsOnOwningThread();
+
+  if (mCache) {
+    mCache->ClearActor();
+    mCache = nullptr;
+  }
+}
+
+mozilla::ipc::IPCResult LocalStorageCacheChild::RecvObserve(
+    const PrincipalInfo& aPrincipalInfo,
+    const PrincipalInfo& aCachePrincipalInfo,
+    const uint32_t& aPrivateBrowsingId, const nsAString& aDocumentURI,
+    const nsAString& aKey, const nsAString& aOldValue,
+    const nsAString& aNewValue) {
+  AssertIsOnOwningThread();
+
+  auto principalOrErr = PrincipalInfoToPrincipal(aPrincipalInfo);
+  if (NS_WARN_IF(principalOrErr.isErr())) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+
+  auto cachePrincipalOrErr = PrincipalInfoToPrincipal(aCachePrincipalInfo);
+  if (NS_WARN_IF(cachePrincipalOrErr.isErr())) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+
+  nsCOMPtr<nsIPrincipal> principal = principalOrErr.unwrap();
+  nsCOMPtr<nsIPrincipal> cachePrincipal = cachePrincipalOrErr.unwrap();
+
+  if (StorageUtils::PrincipalsEqual(principal, cachePrincipal)) {
+    Storage::NotifyChange(/* aStorage */ nullptr, principal, aKey, aOldValue,
+                          aNewValue,
+                          /* aStorageType */ u"localStorage", aDocumentURI,
+                          /* aIsPrivate */ !!aPrivateBrowsingId,
+                          /* aImmediateDispatch */ true);
+  }
+
+  return IPC_OK();
+}
+
+// ----------------------------------------------------------------------------
+// Child
+// ----------------------------------------------------------------------------
+
+class StorageDBChild::ShutdownObserver final : public nsIObserver {
+  // Expected to be only 0 or 1.
+  const uint32_t mPrivateBrowsingId;
+
+ public:
+  explicit ShutdownObserver(const uint32_t aPrivateBrowsingId)
+      : mPrivateBrowsingId(aPrivateBrowsingId) {
+    MOZ_ASSERT(NS_IsMainThread());
+    MOZ_RELEASE_ASSERT(aPrivateBrowsingId < kPrivateBrowsingIdCount);
+  }
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+ private:
+  ~ShutdownObserver() { MOZ_ASSERT(NS_IsMainThread()); }
+};
+
+void StorageDBChild::AddIPDLReference() {
+  MOZ_ASSERT(!mIPCOpen, "Attempting to retain multiple IPDL references");
+  mIPCOpen = true;
+  AddRef();
+}
+
+void StorageDBChild::ReleaseIPDLReference() {
+  MOZ_ASSERT(mIPCOpen, "Attempting to release non-existent IPDL reference");
+  mIPCOpen = false;
+  Release();
+}
+
+StorageDBChild::StorageDBChild(LocalStorageManager* aManager,
+                               const uint32_t aPrivateBrowsingId)
+    : mManager(aManager),
+      mPrivateBrowsingId(aPrivateBrowsingId),
+      mStatus(NS_OK),
+      mIPCOpen(false) {
+  MOZ_RELEASE_ASSERT(aPrivateBrowsingId < kPrivateBrowsingIdCount);
+  MOZ_ASSERT(!NextGenLocalStorageEnabled());
+}
+
+StorageDBChild::~StorageDBChild() = default;
+
+// static
+StorageDBChild* StorageDBChild::Get(const uint32_t aPrivateBrowsingId) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_RELEASE_ASSERT(aPrivateBrowsingId < kPrivateBrowsingIdCount);
+  MOZ_ASSERT(!NextGenLocalStorageEnabled());
+
+  return sStorageChild[aPrivateBrowsingId];
+}
+
+// static
+StorageDBChild* StorageDBChild::GetOrCreate(const uint32_t aPrivateBrowsingId) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_RELEASE_ASSERT(aPrivateBrowsingId < kPrivateBrowsingIdCount);
+  MOZ_ASSERT(!NextGenLocalStorageEnabled());
+
+  StorageDBChild*& storageChild = sStorageChild[aPrivateBrowsingId];
+  if (storageChild || sStorageChildDown[aPrivateBrowsingId]) {
+    // When sStorageChildDown is at true, sStorageChild is null.
+    // Checking sStorageChildDown flag here prevents reinitialization of
+    // the storage child after shutdown.
+    return storageChild;
+  }
+
+  // Use LocalStorageManager::Ensure in case we're called from
+  // DOMSessionStorageManager's initializer and we haven't yet initialized the
+  // local storage manager.
+  RefPtr<StorageDBChild> newStorageChild =
+      new StorageDBChild(LocalStorageManager::Ensure(), aPrivateBrowsingId);
+
+  nsresult rv = newStorageChild->Init();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return nullptr;
+  }
+
+  newStorageChild.forget(&storageChild);
+
+  return storageChild;
+}
+
+nsTHashSet<nsCString>& StorageDBChild::OriginsHavingData() {
+  if (!mOriginsHavingData) {
+    mOriginsHavingData = MakeUnique<nsTHashSet<nsCString>>();
+  }
+
+  return *mOriginsHavingData;
+}
+
+nsresult StorageDBChild::Init() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  ::mozilla::ipc::PBackgroundChild* actor =
+      ::mozilla::ipc::BackgroundChild::GetOrCreateForCurrentThread();
+  if (NS_WARN_IF(!actor)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsString profilePath;
+  if (XRE_IsParentProcess() && mPrivateBrowsingId == 0) {
+    nsresult rv = StorageDBThread::GetProfilePath(profilePath);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+  AddIPDLReference();
+
+  actor->SendPBackgroundStorageConstructor(this, profilePath,
+                                           mPrivateBrowsingId);
+
+  nsCOMPtr<nsIObserverService> observerService = services::GetObserverService();
+  MOZ_ASSERT(observerService);
+
+  nsCOMPtr<nsIObserver> observer = new ShutdownObserver(mPrivateBrowsingId);
+
+  MOZ_ALWAYS_SUCCEEDS(
+      observerService->AddObserver(observer, "xpcom-shutdown", false));
+
+  return NS_OK;
+}
+
+nsresult StorageDBChild::Shutdown() {
+  // There is nothing to do here, IPC will release automatically and
+  // the actual thread running on the parent process will also stop
+  // automatically in profile-before-change topic observer.
+  return NS_OK;
+}
+
+void StorageDBChild::AsyncPreload(LocalStorageCacheBridge* aCache,
+                                  bool aPriority) {
+  if (mIPCOpen) {
+    // Adding ref to cache for the time of preload.  This ensures a reference to
+    // to the cache and that all keys will load into this cache object.
+    mLoadingCaches.Insert(aCache);
+    SendAsyncPreload(aCache->OriginSuffix(), aCache->OriginNoSuffix(),
+                     aPriority);
+  } else {
+    // No IPC, no love.  But the LoadDone call is expected.
+    aCache->LoadDone(NS_ERROR_UNEXPECTED);
+  }
+}
+
+void StorageDBChild::AsyncGetUsage(StorageUsageBridge* aUsage) {
+  if (mIPCOpen) {
+    SendAsyncGetUsage(aUsage->OriginScope());
+  }
+}
+
+void StorageDBChild::SyncPreload(LocalStorageCacheBridge* aCache,
+                                 bool aForceSync) {
+  if (NS_FAILED(mStatus)) {
+    aCache->LoadDone(mStatus);
+    return;
+  }
+
+  if (!mIPCOpen) {
+    aCache->LoadDone(NS_ERROR_UNEXPECTED);
+    return;
+  }
+
+  // There is no way to put the child process to a wait state to receive all
+  // incoming async responses from the parent, hence we have to do a sync
+  // preload instead.  We are smart though, we only demand keys that are left to
+  // load in case the async preload has already loaded some keys.
+  nsTArray<nsString> keys, values;
+  nsresult rv;
+  SendPreload(aCache->OriginSuffix(), aCache->OriginNoSuffix(),
+              aCache->LoadedCount(), &keys, &values, &rv);
+
+  for (uint32_t i = 0; i < keys.Length(); ++i) {
+    aCache->LoadItem(keys[i], values[i]);
+  }
+
+  aCache->LoadDone(rv);
+}
+
+nsresult StorageDBChild::AsyncAddItem(LocalStorageCacheBridge* aCache,
+                                      const nsAString& aKey,
+                                      const nsAString& aValue) {
+  if (NS_FAILED(mStatus) || !mIPCOpen) {
+    return mStatus;
+  }
+
+  SendAsyncAddItem(aCache->OriginSuffix(), aCache->OriginNoSuffix(),
+                   nsString(aKey), nsString(aValue));
+  OriginsHavingData().Insert(aCache->Origin());
+  return NS_OK;
+}
+
+nsresult StorageDBChild::AsyncUpdateItem(LocalStorageCacheBridge* aCache,
+                                         const nsAString& aKey,
+                                         const nsAString& aValue) {
+  if (NS_FAILED(mStatus) || !mIPCOpen) {
+    return mStatus;
+  }
+
+  SendAsyncUpdateItem(aCache->OriginSuffix(), aCache->OriginNoSuffix(),
+                      nsString(aKey), nsString(aValue));
+  OriginsHavingData().Insert(aCache->Origin());
+  return NS_OK;
+}
+
+nsresult StorageDBChild::AsyncRemoveItem(LocalStorageCacheBridge* aCache,
+                                         const nsAString& aKey) {
+  if (NS_FAILED(mStatus) || !mIPCOpen) {
+    return mStatus;
+  }
+
+  SendAsyncRemoveItem(aCache->OriginSuffix(), aCache->OriginNoSuffix(),
+                      nsString(aKey));
+  return NS_OK;
+}
+
+nsresult StorageDBChild::AsyncClear(LocalStorageCacheBridge* aCache) {
+  if (NS_FAILED(mStatus) || !mIPCOpen) {
+    return mStatus;
+  }
+
+  SendAsyncClear(aCache->OriginSuffix(), aCache->OriginNoSuffix());
+  OriginsHavingData().Remove(aCache->Origin());
+  return NS_OK;
+}
+
+bool StorageDBChild::ShouldPreloadOrigin(const nsACString& aOrigin) {
+  // Return true if we didn't receive the origins list yet.
+  // I tend to rather preserve a bit of early-after-start performance
+  // than a bit of memory here.
+  return !mOriginsHavingData || mOriginsHavingData->Contains(aOrigin);
+}
+
+mozilla::ipc::IPCResult StorageDBChild::RecvObserve(
+    const nsACString& aTopic, const nsAString& aOriginAttributesPattern,
+    const nsACString& aOriginScope) {
+  MOZ_ASSERT(!XRE_IsParentProcess());
+
+  if (StorageObserver* obs = StorageObserver::Self()) {
+    obs->Notify(PromiseFlatCString(aTopic).get(), aOriginAttributesPattern,
+                aOriginScope);
+  }
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBChild::RecvOriginsHavingData(
+    nsTArray<nsCString>&& aOrigins) {
+  // Force population of mOriginsHavingData even if there are no origins so that
+  // ShouldPreloadOrigin does not generate false positives for all origins.
+  if (!aOrigins.Length()) {
+    Unused << OriginsHavingData();
+  }
+
+  for (uint32_t i = 0; i < aOrigins.Length(); ++i) {
+    OriginsHavingData().Insert(aOrigins[i]);
+  }
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBChild::RecvLoadItem(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix,
+    const nsAString& aKey, const nsAString& aValue) {
+  LocalStorageCache* aCache =
+      mManager->GetCache(aOriginSuffix, aOriginNoSuffix);
+  if (aCache) {
+    aCache->LoadItem(aKey, aValue);
+  }
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBChild::RecvLoadDone(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix,
+    const nsresult& aRv) {
+  LocalStorageCache* aCache =
+      mManager->GetCache(aOriginSuffix, aOriginNoSuffix);
+  if (aCache) {
+    aCache->LoadDone(aRv);
+
+    // Just drop reference to this cache now since the load is done.
+    mLoadingCaches.Remove(static_cast<LocalStorageCacheBridge*>(aCache));
+  }
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBChild::RecvLoadUsage(
+    const nsACString& aOriginNoSuffix, const int64_t& aUsage) {
+  RefPtr<StorageUsageBridge> scopeUsage =
+      mManager->GetOriginUsage(aOriginNoSuffix, mPrivateBrowsingId);
+  scopeUsage->LoadUsage(aUsage);
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBChild::RecvError(const nsresult& aRv) {
+  mStatus = aRv;
+  return IPC_OK();
+}
+
+NS_IMPL_ISUPPORTS(StorageDBChild::ShutdownObserver, nsIObserver)
+
+NS_IMETHODIMP
+StorageDBChild::ShutdownObserver::Observe(nsISupports* aSubject,
+                                          const char* aTopic,
+                                          const char16_t* aData) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!strcmp(aTopic, "xpcom-shutdown"));
+
+  nsCOMPtr<nsIObserverService> observerService =
+      mozilla::services::GetObserverService();
+  if (NS_WARN_IF(!observerService)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  Unused << observerService->RemoveObserver(this, "xpcom-shutdown");
+
+  StorageDBChild*& storageChild = sStorageChild[mPrivateBrowsingId];
+  if (storageChild) {
+    sStorageChildDown[mPrivateBrowsingId] = true;
+
+    MOZ_ALWAYS_TRUE(storageChild->PBackgroundStorageChild::SendDeleteMe());
+
+    NS_RELEASE(storageChild);
+    storageChild = nullptr;
+  }
+
+  return NS_OK;
+}
+
+SessionStorageObserverChild::SessionStorageObserverChild(
+    SessionStorageObserver* aObserver)
+    : mObserver(aObserver) {
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(NextGenLocalStorageEnabled());
+  MOZ_ASSERT(aObserver);
+  aObserver->AssertIsOnOwningThread();
+
+  MOZ_COUNT_CTOR(SessionStorageObserverChild);
+}
+
+SessionStorageObserverChild::~SessionStorageObserverChild() {
+  AssertIsOnOwningThread();
+
+  MOZ_COUNT_DTOR(SessionStorageObserverChild);
+}
+
+void SessionStorageObserverChild::SendDeleteMeInternal() {
+  AssertIsOnOwningThread();
+
+  if (mObserver) {
+    mObserver->ClearActor();
+    mObserver = nullptr;
+
+    // Don't check result here since IPC may no longer be available due to
+    // SessionStorageManager (which holds a strong reference to
+    // SessionStorageObserver) being destroyed very late in the game.
+    PSessionStorageObserverChild::SendDeleteMe();
+  }
+}
+
+void SessionStorageObserverChild::ActorDestroy(ActorDestroyReason aWhy) {
+  AssertIsOnOwningThread();
+
+  if (mObserver) {
+    mObserver->ClearActor();
+    mObserver = nullptr;
+  }
+}
+
+mozilla::ipc::IPCResult SessionStorageObserverChild::RecvObserve(
+    const nsACString& aTopic, const nsAString& aOriginAttributesPattern,
+    const nsACString& aOriginScope) {
+  AssertIsOnOwningThread();
+
+  if (StorageObserver* obs = StorageObserver::Self()) {
+    obs->Notify(PromiseFlatCString(aTopic).get(), aOriginAttributesPattern,
+                aOriginScope);
+  }
+
+  return IPC_OK();
+}
+
+SessionStorageCacheChild::SessionStorageCacheChild(SessionStorageCache* aCache)
+    : mCache(aCache) {
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mCache);
+
+  MOZ_COUNT_CTOR(SessionStorageCacheChild);
+}
+
+SessionStorageCacheChild::~SessionStorageCacheChild() {
+  AssertIsOnOwningThread();
+
+  MOZ_COUNT_DTOR(SessionStorageCacheChild);
+}
+
+void SessionStorageCacheChild::SendDeleteMeInternal() {
+  AssertIsOnOwningThread();
+
+  if (mCache) {
+    mCache->ClearActor();
+    mCache = nullptr;
+
+    MOZ_ALWAYS_TRUE(PBackgroundSessionStorageCacheChild::SendDeleteMe());
+  }
+}
+
+void SessionStorageCacheChild::ActorDestroy(ActorDestroyReason aWhy) {
+  AssertIsOnOwningThread();
+
+  if (mCache) {
+    mCache->ClearActor();
+    mCache = nullptr;
+  }
+}
+
+SessionStorageManagerChild::SessionStorageManagerChild(
+    SessionStorageManager* aSSManager)
+    : mSSManager(aSSManager) {
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mSSManager);
+
+  MOZ_COUNT_CTOR(SessionStorageManagerChild);
+}
+
+SessionStorageManagerChild::~SessionStorageManagerChild() {
+  AssertIsOnOwningThread();
+
+  MOZ_COUNT_DTOR(SessionStorageManagerChild);
+}
+
+void SessionStorageManagerChild::SendDeleteMeInternal() {
+  AssertIsOnOwningThread();
+
+  if (mSSManager) {
+    mSSManager->ClearActor();
+    mSSManager = nullptr;
+
+    MOZ_ALWAYS_TRUE(PBackgroundSessionStorageManagerChild::SendDeleteMe());
+  }
+}
+
+void SessionStorageManagerChild::ActorDestroy(ActorDestroyReason aWhy) {
+  AssertIsOnOwningThread();
+
+  if (mSSManager) {
+    mSSManager->ClearActor();
+    mSSManager = nullptr;
+  }
+}
+
+mozilla::ipc::IPCResult SessionStorageManagerChild::RecvClearStoragesForOrigin(
+    const nsACString& aOriginAttrs, const nsACString& aOriginKey) {
+  AssertIsOnOwningThread();
+
+  if (mSSManager) {
+    mSSManager->ClearStoragesForOrigin(aOriginAttrs, aOriginKey);
+  }
+
+  return IPC_OK();
+}
+
+LocalStorageCacheParent::LocalStorageCacheParent(
+    const mozilla::ipc::PrincipalInfo& aPrincipalInfo,
+    const nsACString& aOriginKey, uint32_t aPrivateBrowsingId)
+    : mPrincipalInfo(aPrincipalInfo),
+      mOriginKey(aOriginKey),
+      mPrivateBrowsingId(aPrivateBrowsingId),
+      mActorDestroyed(false) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+}
+
+LocalStorageCacheParent::~LocalStorageCacheParent() {
+  MOZ_ASSERT(mActorDestroyed);
+}
+
+void LocalStorageCacheParent::ActorDestroy(ActorDestroyReason aWhy) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mActorDestroyed);
+
+  mActorDestroyed = true;
+
+  MOZ_ASSERT(gLocalStorageCacheParents);
+
+  nsTArray<LocalStorageCacheParent*>* array;
+  gLocalStorageCacheParents->Get(mOriginKey, &array);
+  MOZ_ASSERT(array);
+
+  array->RemoveElement(this);
+
+  if (array->IsEmpty()) {
+    gLocalStorageCacheParents->Remove(mOriginKey);
+  }
+
+  if (!gLocalStorageCacheParents->Count()) {
+    gLocalStorageCacheParents = nullptr;
+  }
+}
+
+mozilla::ipc::IPCResult LocalStorageCacheParent::RecvDeleteMe() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mActorDestroyed);
+
+  IProtocol* mgr = Manager();
+  if (!PBackgroundLocalStorageCacheParent::Send__delete__(this)) {
+    return IPC_FAIL_NO_REASON(mgr);
+  }
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult LocalStorageCacheParent::RecvNotify(
+    const nsAString& aDocumentURI, const nsAString& aKey,
+    const nsAString& aOldValue, const nsAString& aNewValue) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(gLocalStorageCacheParents);
+
+  nsTArray<LocalStorageCacheParent*>* array;
+  gLocalStorageCacheParents->Get(mOriginKey, &array);
+  MOZ_ASSERT(array);
+
+  for (LocalStorageCacheParent* localStorageCacheParent : *array) {
+    if (localStorageCacheParent != this) {
+      // When bug 1443925 is fixed, we can compare mPrincipalInfo against
+      // localStorageCacheParent->PrincipalInfo() here on the background thread
+      // instead of posting it to the main thread.  The advantage of doing so is
+      // that it would save an IPC message in the case where the principals do
+      // not match.
+      Unused << localStorageCacheParent->SendObserve(
+          mPrincipalInfo, localStorageCacheParent->PrincipalInfo(),
+          mPrivateBrowsingId, aDocumentURI, aKey, aOldValue, aNewValue);
+    }
+  }
+
+  return IPC_OK();
+}
+
+// ----------------------------------------------------------------------------
+// Parent
+// ----------------------------------------------------------------------------
+
+class StorageDBParent::ObserverSink : public StorageObserverSink {
+  nsCOMPtr<nsIEventTarget> mOwningEventTarget;
+
+  // Only touched on the PBackground thread.
+  StorageDBParent* MOZ_NON_OWNING_REF mActor;
+
+ public:
+  explicit ObserverSink(StorageDBParent* aActor)
+      : mOwningEventTarget(GetCurrentSerialEventTarget()), mActor(aActor) {
+    ::mozilla::ipc::AssertIsOnBackgroundThread();
+    MOZ_ASSERT(aActor);
+  }
+
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(StorageDBParent::ObserverSink);
+
+  void Start();
+
+  void Stop();
+
+ private:
+  ~ObserverSink() = default;
+
+  void AddSink();
+
+  void RemoveSink();
+
+  void Notify(const nsACString& aTopic,
+              const nsAString& aOriginAttributesPattern,
+              const nsACString& aOriginScope);
+
+  // StorageObserverSink
+  nsresult Observe(const char* aTopic, const nsAString& aOriginAttrPattern,
+                   const nsACString& aOriginScope) override;
+};
+
+NS_IMPL_ADDREF(StorageDBParent)
+NS_IMPL_RELEASE(StorageDBParent)
+
+void StorageDBParent::AddIPDLReference() {
+  MOZ_ASSERT(!mIPCOpen, "Attempting to retain multiple IPDL references");
+  mIPCOpen = true;
+  AddRef();
+}
+
+void StorageDBParent::ReleaseIPDLReference() {
+  MOZ_ASSERT(mIPCOpen, "Attempting to release non-existent IPDL reference");
+  mIPCOpen = false;
+  Release();
+}
+
+namespace {}  // namespace
+
+StorageDBParent::StorageDBParent(const nsAString& aProfilePath,
+                                 const uint32_t aPrivateBrowsingId)
+    : mProfilePath(aProfilePath),
+      mPrivateBrowsingId(aPrivateBrowsingId),
+      mIPCOpen(false) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  // We are always open by IPC only
+  AddIPDLReference();
+}
+
+StorageDBParent::~StorageDBParent() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  if (mObserverSink) {
+    mObserverSink->Stop();
+    mObserverSink = nullptr;
+  }
+}
+
+void StorageDBParent::Init() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  PBackgroundParent* actor = Manager();
+  MOZ_ASSERT(actor);
+
+  if (::mozilla::ipc::BackgroundParent::IsOtherProcessActor(actor)) {
+    mObserverSink = new ObserverSink(this);
+    mObserverSink->Start();
+  }
+
+  StorageDBThread* storageThread = StorageDBThread::Get(mPrivateBrowsingId);
+  if (storageThread) {
+    nsTArray<nsCString> scopes;
+    storageThread->GetOriginsHavingData(&scopes);
+    mozilla::Unused << SendOriginsHavingData(scopes);
+  }
+}
+
+StorageDBParent::CacheParentBridge* StorageDBParent::NewCache(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix) {
+  return new CacheParentBridge(this, aOriginSuffix, aOriginNoSuffix);
+}
+
+void StorageDBParent::ActorDestroy(ActorDestroyReason aWhy) {
+  // Implement me! Bug 1005169
+}
+
+mozilla::ipc::IPCResult StorageDBParent::RecvDeleteMe() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  IProtocol* mgr = Manager();
+  if (!PBackgroundStorageParent::Send__delete__(this)) {
+    return IPC_FAIL_NO_REASON(mgr);
+  }
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBParent::RecvAsyncPreload(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix,
+    const bool& aPriority) {
+  StorageDBThread* storageThread =
+      StorageDBThread::GetOrCreate(mProfilePath, mPrivateBrowsingId);
+  if (!storageThread) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+
+  storageThread->AsyncPreload(NewCache(aOriginSuffix, aOriginNoSuffix),
+                              aPriority);
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBParent::RecvAsyncGetUsage(
+    const nsACString& aOriginNoSuffix) {
+  StorageDBThread* storageThread =
+      StorageDBThread::GetOrCreate(mProfilePath, mPrivateBrowsingId);
+  if (!storageThread) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+
+  // The object releases it self in LoadUsage method
+  RefPtr<UsageParentBridge> usage =
+      new UsageParentBridge(this, aOriginNoSuffix);
+
+  storageThread->AsyncGetUsage(usage);
+
+  return IPC_OK();
+}
+
+namespace {
+
+// We need another implementation of LocalStorageCacheBridge to do
+// synchronous IPC preload.  This class just receives Load* notifications
+// and fills the returning arguments of RecvPreload with the database
+// values for us.
+class SyncLoadCacheHelper : public LocalStorageCacheBridge {
+ public:
+  SyncLoadCacheHelper(const nsACString& aOriginSuffix,
+                      const nsACString& aOriginNoSuffix,
+                      uint32_t aAlreadyLoadedCount, nsTArray<nsString>* aKeys,
+                      nsTArray<nsString>* aValues, nsresult* rv)
+      : mMonitor("DOM Storage SyncLoad IPC"),
+        mSuffix(aOriginSuffix),
+        mOrigin(aOriginNoSuffix),
+        mKeys(aKeys),
+        mValues(aValues),
+        mRv(rv),
+        mLoaded(false),
+        mLoadedCount(aAlreadyLoadedCount) {
+    // Precaution
+    *mRv = NS_ERROR_UNEXPECTED;
+  }
+
+  virtual const nsCString Origin() const override {
+    return LocalStorageManager::CreateOrigin(mSuffix, mOrigin);
+  }
+  virtual const nsCString& OriginNoSuffix() const override { return mOrigin; }
+  virtual const nsCString& OriginSuffix() const override { return mSuffix; }
+  virtual bool Loaded() override { return mLoaded; }
+  virtual uint32_t LoadedCount() override { return mLoadedCount; }
+  virtual bool LoadItem(const nsAString& aKey,
+                        const nsAString& aValue) override {
+    // Called on the aCache background thread
+    MOZ_ASSERT(!mLoaded);
+    if (mLoaded) {
+      return false;
+    }
+
+    ++mLoadedCount;
+    mKeys->AppendElement(aKey);
+    mValues->AppendElement(aValue);
+    return true;
+  }
+
+  virtual void LoadDone(nsresult aRv) override {
+    // Called on the aCache background thread
+    MonitorAutoLock monitor(mMonitor);
+    MOZ_ASSERT(!mLoaded && mRv);
+    mLoaded = true;
+    if (mRv) {
+      *mRv = aRv;
+      mRv = nullptr;
+    }
+    monitor.Notify();
+  }
+
+  virtual void LoadWait() override {
+    // Called on the main thread, exits after LoadDone() call
+    MonitorAutoLock monitor(mMonitor);
+    while (!mLoaded) {
+      monitor.Wait();
+    }
+  }
+
+ private:
+  Monitor mMonitor MOZ_UNANNOTATED;
+  nsCString mSuffix, mOrigin;
+  nsTArray<nsString>* mKeys;
+  nsTArray<nsString>* mValues;
+  nsresult* mRv;
+  bool mLoaded;
+  uint32_t mLoadedCount;
+};
+
+}  // namespace
+
+mozilla::ipc::IPCResult StorageDBParent::RecvPreload(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix,
+    const uint32_t& aAlreadyLoadedCount, nsTArray<nsString>* aKeys,
+    nsTArray<nsString>* aValues, nsresult* aRv) {
+  StorageDBThread* storageThread =
+      StorageDBThread::GetOrCreate(mProfilePath, mPrivateBrowsingId);
+  if (!storageThread) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+
+  RefPtr<SyncLoadCacheHelper> cache(
+      new SyncLoadCacheHelper(aOriginSuffix, aOriginNoSuffix,
+                              aAlreadyLoadedCount, aKeys, aValues, aRv));
+
+  storageThread->SyncPreload(cache, true);
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBParent::RecvAsyncAddItem(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix,
+    const nsAString& aKey, const nsAString& aValue) {
+  StorageDBThread* storageThread =
+      StorageDBThread::GetOrCreate(mProfilePath, mPrivateBrowsingId);
+  if (!storageThread) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+
+  nsresult rv = storageThread->AsyncAddItem(
+      NewCache(aOriginSuffix, aOriginNoSuffix), aKey, aValue);
+  if (NS_FAILED(rv) && mIPCOpen) {
+    mozilla::Unused << SendError(rv);
+  }
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBParent::RecvAsyncUpdateItem(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix,
+    const nsAString& aKey, const nsAString& aValue) {
+  StorageDBThread* storageThread =
+      StorageDBThread::GetOrCreate(mProfilePath, mPrivateBrowsingId);
+  if (!storageThread) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+
+  nsresult rv = storageThread->AsyncUpdateItem(
+      NewCache(aOriginSuffix, aOriginNoSuffix), aKey, aValue);
+  if (NS_FAILED(rv) && mIPCOpen) {
+    mozilla::Unused << SendError(rv);
+  }
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBParent::RecvAsyncRemoveItem(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix,
+    const nsAString& aKey) {
+  StorageDBThread* storageThread =
+      StorageDBThread::GetOrCreate(mProfilePath, mPrivateBrowsingId);
+  if (!storageThread) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+
+  nsresult rv = storageThread->AsyncRemoveItem(
+      NewCache(aOriginSuffix, aOriginNoSuffix), aKey);
+  if (NS_FAILED(rv) && mIPCOpen) {
+    mozilla::Unused << SendError(rv);
+  }
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBParent::RecvAsyncClear(
+    const nsACString& aOriginSuffix, const nsACString& aOriginNoSuffix) {
+  StorageDBThread* storageThread =
+      StorageDBThread::GetOrCreate(mProfilePath, mPrivateBrowsingId);
+  if (!storageThread) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+
+  nsresult rv =
+      storageThread->AsyncClear(NewCache(aOriginSuffix, aOriginNoSuffix));
+  if (NS_FAILED(rv) && mIPCOpen) {
+    mozilla::Unused << SendError(rv);
+  }
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBParent::RecvAsyncFlush() {
+  StorageDBThread* storageThread = StorageDBThread::Get(mPrivateBrowsingId);
+  if (!storageThread) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+
+  storageThread->AsyncFlush();
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBParent::RecvStartup() {
+  StorageDBThread* storageThread =
+      StorageDBThread::GetOrCreate(mProfilePath, mPrivateBrowsingId);
+  if (!storageThread) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBParent::RecvClearAll() {
+  StorageDBThread* storageThread =
+      StorageDBThread::GetOrCreate(mProfilePath, mPrivateBrowsingId);
+  if (!storageThread) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+
+  storageThread->AsyncClearAll();
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBParent::RecvClearMatchingOrigin(
+    const nsACString& aOriginNoSuffix) {
+  StorageDBThread* storageThread =
+      StorageDBThread::GetOrCreate(mProfilePath, mPrivateBrowsingId);
+  if (!storageThread) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+
+  storageThread->AsyncClearMatchingOrigin(aOriginNoSuffix);
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult StorageDBParent::RecvClearMatchingOriginAttributes(
+    const OriginAttributesPattern& aPattern) {
+  StorageDBThread* storageThread =
+      StorageDBThread::GetOrCreate(mProfilePath, mPrivateBrowsingId);
+  if (!storageThread) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+
+  storageThread->AsyncClearMatchingOriginAttributes(aPattern);
+
+  return IPC_OK();
+}
+
+void StorageDBParent::Observe(const nsACString& aTopic,
+                              const nsAString& aOriginAttributesPattern,
+                              const nsACString& aOriginScope) {
+  if (mIPCOpen) {
+    mozilla::Unused << SendObserve(aTopic, aOriginAttributesPattern,
+                                   aOriginScope);
+  }
+}
+
+namespace {
+
+// Results must be sent back on the main thread
+class LoadRunnable : public Runnable {
+ public:
+  enum TaskType { loadItem, loadDone };
+
+  LoadRunnable(StorageDBParent* aParent, TaskType aType,
+               const nsACString& aOriginSuffix,
+               const nsACString& aOriginNoSuffix,
+               const nsAString& aKey = u""_ns, const nsAString& aValue = u""_ns)
+      : Runnable("dom::LoadRunnable"),
+        mParent(aParent),
+        mType(aType),
+        mSuffix(aOriginSuffix),
+        mOrigin(aOriginNoSuffix),
+        mKey(aKey),
+        mValue(aValue),
+        mRv(NS_ERROR_NOT_INITIALIZED) {}
+
+  LoadRunnable(StorageDBParent* aParent, TaskType aType,
+               const nsACString& aOriginSuffix,
+               const nsACString& aOriginNoSuffix, nsresult aRv)
+      : Runnable("dom::LoadRunnable"),
+        mParent(aParent),
+        mType(aType),
+        mSuffix(aOriginSuffix),
+        mOrigin(aOriginNoSuffix),
+        mRv(aRv) {}
+
+ private:
+  RefPtr<StorageDBParent> mParent;
+  TaskType mType;
+  nsCString mSuffix, mOrigin;
+  nsString mKey;
+  nsString mValue;
+  nsresult mRv;
+
+  NS_IMETHOD Run() override {
+    if (!mParent->IPCOpen()) {
+      return NS_OK;
+    }
+
+    switch (mType) {
+      case loadItem:
+        mozilla::Unused << mParent->SendLoadItem(mSuffix, mOrigin, mKey,
+                                                 mValue);
+        break;
+      case loadDone:
+        mozilla::Unused << mParent->SendLoadDone(mSuffix, mOrigin, mRv);
+        break;
+    }
+
+    mParent = nullptr;
+
+    return NS_OK;
+  }
+};
+
+}  // namespace
+
+// StorageDBParent::CacheParentBridge
+
+const nsCString StorageDBParent::CacheParentBridge::Origin() const {
+  return LocalStorageManager::CreateOrigin(mOriginSuffix, mOriginNoSuffix);
+}
+
+bool StorageDBParent::CacheParentBridge::LoadItem(const nsAString& aKey,
+                                                  const nsAString& aValue) {
+  if (mLoaded) {
+    return false;
+  }
+
+  ++mLoadedCount;
+
+  RefPtr<LoadRunnable> r =
+      new LoadRunnable(mParent, LoadRunnable::loadItem, mOriginSuffix,
+                       mOriginNoSuffix, aKey, aValue);
+
+  MOZ_ALWAYS_SUCCEEDS(mOwningEventTarget->Dispatch(r, NS_DISPATCH_NORMAL));
+
+  return true;
+}
+
+void StorageDBParent::CacheParentBridge::LoadDone(nsresult aRv) {
+  // Prevent send of duplicate LoadDone.
+  if (mLoaded) {
+    return;
+  }
+
+  mLoaded = true;
+
+  RefPtr<LoadRunnable> r = new LoadRunnable(
+      mParent, LoadRunnable::loadDone, mOriginSuffix, mOriginNoSuffix, aRv);
+
+  MOZ_ALWAYS_SUCCEEDS(mOwningEventTarget->Dispatch(r, NS_DISPATCH_NORMAL));
+}
+
+void StorageDBParent::CacheParentBridge::LoadWait() {
+  // Should never be called on this implementation
+  MOZ_ASSERT(false);
+}
+
+// XXX Fix me!
+// This should be just:
+// NS_IMPL_RELEASE_WITH_DESTROY(StorageDBParent::CacheParentBridge, Destroy)
+// But due to different strings used for refcount logging and different return
+// types, this is done manually for now.
+NS_IMETHODIMP_(void)
+StorageDBParent::CacheParentBridge::Release(void) {
+  MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");
+  nsrefcnt count = --mRefCnt;
+  NS_LOG_RELEASE(this, count, "LocalStorageCacheBridge");
+  if (0 == count) {
+    mRefCnt = 1; /* stabilize */
+    /* enable this to find non-threadsafe destructors: */
+    /* NS_ASSERT_OWNINGTHREAD(_class); */
+    Destroy();
+  }
+}
+
+void StorageDBParent::CacheParentBridge::Destroy() {
+  if (mOwningEventTarget->IsOnCurrentThread()) {
+    delete this;
+    return;
+  }
+
+  RefPtr<Runnable> destroyRunnable = NewNonOwningRunnableMethod(
+      "CacheParentBridge::Destroy", this, &CacheParentBridge::Destroy);
+
+  MOZ_ALWAYS_SUCCEEDS(
+      mOwningEventTarget->Dispatch(destroyRunnable, NS_DISPATCH_NORMAL));
+}
+
+// StorageDBParent::UsageParentBridge
+
+namespace {
+
+class UsageRunnable : public Runnable {
+ public:
+  UsageRunnable(StorageDBParent* aParent, const nsACString& aOriginScope,
+                const int64_t& aUsage)
+      : Runnable("dom::UsageRunnable"),
+        mParent(aParent),
+        mOriginScope(aOriginScope),
+        mUsage(aUsage) {}
+
+ private:
+  NS_IMETHOD Run() override {
+    if (!mParent->IPCOpen()) {
+      return NS_OK;
+    }
+
+    mozilla::Unused << mParent->SendLoadUsage(mOriginScope, mUsage);
+
+    mParent = nullptr;
+
+    return NS_OK;
+  }
+
+  RefPtr<StorageDBParent> mParent;
+  nsCString mOriginScope;
+  int64_t mUsage;
+};
+
+}  // namespace
+
+void StorageDBParent::UsageParentBridge::LoadUsage(const int64_t aUsage) {
+  RefPtr<UsageRunnable> r = new UsageRunnable(mParent, mOriginScope, aUsage);
+
+  MOZ_ALWAYS_SUCCEEDS(mOwningEventTarget->Dispatch(r, NS_DISPATCH_NORMAL));
+}
+
+// XXX Fix me!
+// This should be just:
+// NS_IMPL_RELEASE_WITH_DESTROY(StorageDBParent::UsageParentBridge, Destroy)
+// But due to different strings used for refcount logging, this is done manually
+// for now.
+NS_IMETHODIMP_(MozExternalRefCountType)
+StorageDBParent::UsageParentBridge::Release(void) {
+  MOZ_ASSERT(int32_t(mRefCnt) > 0, "dup release");
+  nsrefcnt count = --mRefCnt;
+  NS_LOG_RELEASE(this, count, "StorageUsageBridge");
+  if (count == 0) {
+    Destroy();
+    return 0;
+  }
+  return count;
+}
+
+void StorageDBParent::UsageParentBridge::Destroy() {
+  if (mOwningEventTarget->IsOnCurrentThread()) {
+    delete this;
+    return;
+  }
+
+  RefPtr<Runnable> destroyRunnable = NewNonOwningRunnableMethod(
+      "UsageParentBridge::Destroy", this, &UsageParentBridge::Destroy);
+
+  MOZ_ALWAYS_SUCCEEDS(
+      mOwningEventTarget->Dispatch(destroyRunnable, NS_DISPATCH_NORMAL));
+}
+
+void StorageDBParent::ObserverSink::Start() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  RefPtr<Runnable> runnable =
+      NewRunnableMethod("StorageDBParent::ObserverSink::AddSink", this,
+                        &StorageDBParent::ObserverSink::AddSink);
+
+  MOZ_ALWAYS_SUCCEEDS(NS_DispatchToMainThread(runnable));
+}
+
+void StorageDBParent::ObserverSink::Stop() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  mActor = nullptr;
+
+  RefPtr<Runnable> runnable =
+      NewRunnableMethod("StorageDBParent::ObserverSink::RemoveSink", this,
+                        &StorageDBParent::ObserverSink::RemoveSink);
+
+  MOZ_ALWAYS_SUCCEEDS(NS_DispatchToMainThread(runnable));
+}
+
+void StorageDBParent::ObserverSink::AddSink() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  StorageObserver* observer = StorageObserver::Self();
+  if (observer) {
+    observer->AddSink(this);
+  }
+}
+
+void StorageDBParent::ObserverSink::RemoveSink() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  StorageObserver* observer = StorageObserver::Self();
+  if (observer) {
+    observer->RemoveSink(this);
+  }
+}
+
+void StorageDBParent::ObserverSink::Notify(
+    const nsACString& aTopic, const nsAString& aOriginAttributesPattern,
+    const nsACString& aOriginScope) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  if (mActor) {
+    mActor->Observe(aTopic, aOriginAttributesPattern, aOriginScope);
+  }
+}
+
+nsresult StorageDBParent::ObserverSink::Observe(
+    const char* aTopic, const nsAString& aOriginAttributesPattern,
+    const nsACString& aOriginScope) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  RefPtr<Runnable> runnable = NewRunnableMethod<nsCString, nsString, nsCString>(
+      "StorageDBParent::ObserverSink::Observe2", this,
+      &StorageDBParent::ObserverSink::Notify, aTopic, aOriginAttributesPattern,
+      aOriginScope);
+
+  MOZ_ALWAYS_SUCCEEDS(
+      mOwningEventTarget->Dispatch(runnable, NS_DISPATCH_NORMAL));
+
+  return NS_OK;
+}
+
+SessionStorageObserverParent::SessionStorageObserverParent()
+    : mActorDestroyed(false) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  StorageObserver* observer = StorageObserver::Self();
+  if (observer) {
+    observer->AddSink(this);
+  }
+}
+
+SessionStorageObserverParent::~SessionStorageObserverParent() {
+  MOZ_ASSERT(mActorDestroyed);
+
+  StorageObserver* observer = StorageObserver::Self();
+  if (observer) {
+    observer->RemoveSink(this);
+  }
+}
+
+void SessionStorageObserverParent::ActorDestroy(ActorDestroyReason aWhy) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!mActorDestroyed);
+
+  mActorDestroyed = true;
+}
+
+mozilla::ipc::IPCResult SessionStorageObserverParent::RecvDeleteMe() {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!mActorDestroyed);
+
+  IProtocol* mgr = Manager();
+  if (!PSessionStorageObserverParent::Send__delete__(this)) {
+    return IPC_FAIL_NO_REASON(mgr);
+  }
+  return IPC_OK();
+}
+
+nsresult SessionStorageObserverParent::Observe(
+    const char* aTopic, const nsAString& aOriginAttributesPattern,
+    const nsACString& aOriginScope) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (!mActorDestroyed) {
+    mozilla::Unused << SendObserve(nsDependentCString(aTopic),
+                                   aOriginAttributesPattern, aOriginScope);
+  }
+  return NS_OK;
+}
+
+SessionStorageCacheParent::SessionStorageCacheParent(
+    const mozilla::ipc::PrincipalInfo& aPrincipalInfo,
+    const nsACString& aOriginKey, SessionStorageManagerParent* aActor)
+    : mPrincipalInfo(aPrincipalInfo),
+      mOriginKey(aOriginKey),
+      mManagerActor(aActor) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mManagerActor);
+}
+
+SessionStorageCacheParent::~SessionStorageCacheParent() = default;
+
+void SessionStorageCacheParent::ActorDestroy(ActorDestroyReason aWhy) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  mManagerActor = nullptr;
+}
+
+mozilla::ipc::IPCResult SessionStorageCacheParent::RecvLoad(
+    nsTArray<SSSetItemInfo>* aData) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mManagerActor);
+
+  mLoadReceived.Flip();
+
+  RefPtr<BackgroundSessionStorageManager> manager = mManagerActor->GetManager();
+  MOZ_ASSERT(manager);
+
+  OriginAttributes attrs;
+  MOZ_ALWAYS_TRUE(
+      StoragePrincipalHelper::GetOriginAttributes(mPrincipalInfo, attrs));
+
+  nsAutoCString originAttrs;
+  attrs.CreateSuffix(originAttrs);
+
+  manager->CopyDataToContentProcess(originAttrs, mOriginKey, *aData);
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult SessionStorageCacheParent::RecvCheckpoint(
+    nsTArray<SSWriteInfo>&& aWriteInfos) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mManagerActor);
+
+  RefPtr<BackgroundSessionStorageManager> manager = mManagerActor->GetManager();
+  MOZ_ASSERT(manager);
+
+  OriginAttributes attrs;
+  StoragePrincipalHelper::GetOriginAttributes(mPrincipalInfo, attrs);
+
+  nsAutoCString originAttrs;
+  attrs.CreateSuffix(originAttrs);
+
+  manager->UpdateData(originAttrs, mOriginKey, aWriteInfos);
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult SessionStorageCacheParent::RecvDeleteMe() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mManagerActor);
+
+  mManagerActor = nullptr;
+
+  IProtocol* mgr = Manager();
+  if (!PBackgroundSessionStorageCacheParent::Send__delete__(this)) {
+    return IPC_FAIL(
+        mgr, "Failed to delete PBackgroundSessionStorageCacheParent actor");
+  }
+  return IPC_OK();
+}
+
+SessionStorageManagerParent::SessionStorageManagerParent(uint64_t aTopContextId)
+    : mBackgroundManager(
+          BackgroundSessionStorageManager::GetOrCreate(aTopContextId)) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mBackgroundManager);
+  mBackgroundManager->AddParticipatingActor(this);
+}
+
+SessionStorageManagerParent::~SessionStorageManagerParent() = default;
+
+void SessionStorageManagerParent::ActorDestroy(ActorDestroyReason aWhy) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  if (mBackgroundManager) {
+    mBackgroundManager->RemoveParticipatingActor(this);
+  }
+
+  mBackgroundManager = nullptr;
+}
+
+already_AddRefed<PBackgroundSessionStorageCacheParent>
+SessionStorageManagerParent::AllocPBackgroundSessionStorageCacheParent(
+    const PrincipalInfo& aPrincipalInfo, const nsACString& aOriginKey) {
+  return MakeAndAddRef<SessionStorageCacheParent>(aPrincipalInfo, aOriginKey,
+                                                  this);
+}
+
+BackgroundSessionStorageManager* SessionStorageManagerParent::GetManager()
+    const {
+  return mBackgroundManager;
+}
+
+mozilla::ipc::IPCResult SessionStorageManagerParent::RecvClearStorages(
+    const OriginAttributesPattern& aPattern, const nsACString& aOriginScope) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  mBackgroundManager->ClearStorages(aPattern, aOriginScope);
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult SessionStorageManagerParent::RecvDeleteMe() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mBackgroundManager);
+
+  mBackgroundManager->RemoveParticipatingActor(this);
+
+  mBackgroundManager = nullptr;
+
+  IProtocol* mgr = Manager();
+  if (!PBackgroundSessionStorageManagerParent::Send__delete__(this)) {
+    return IPC_FAIL(
+        mgr, "Failed to delete PBackgroundSessionStorageManagerParent actor");
+  }
+  return IPC_OK();
+}
+
+/*******************************************************************************
+ * Exported functions
+ ******************************************************************************/
+
+PBackgroundLocalStorageCacheParent* AllocPBackgroundLocalStorageCacheParent(
+    const mozilla::ipc::PrincipalInfo& aPrincipalInfo,
+    const nsACString& aOriginKey, const uint32_t& aPrivateBrowsingId) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  RefPtr<LocalStorageCacheParent> actor = new LocalStorageCacheParent(
+      aPrincipalInfo, aOriginKey, aPrivateBrowsingId);
+
+  // Transfer ownership to IPDL.
+  return actor.forget().take();
+}
+
+mozilla::ipc::IPCResult RecvPBackgroundLocalStorageCacheConstructor(
+    mozilla::ipc::PBackgroundParent* aBackgroundActor,
+    PBackgroundLocalStorageCacheParent* aActor,
+    const mozilla::ipc::PrincipalInfo& aPrincipalInfo,
+    const nsACString& aOriginKey, const uint32_t& aPrivateBrowsingId) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+
+  auto* actor = static_cast<LocalStorageCacheParent*>(aActor);
+
+  if (!gLocalStorageCacheParents) {
+    gLocalStorageCacheParents = new LocalStorageCacheParentHashtable();
+  }
+
+  gLocalStorageCacheParents->GetOrInsertNew(aOriginKey)->AppendElement(actor);
+
+  // We are currently trusting the content process not to lie to us.  It is
+  // future work to consult the ClientManager to determine whether this is a
+  // legitimate origin for the content process.
+
+  return IPC_OK();
+}
+
+bool DeallocPBackgroundLocalStorageCacheParent(
+    PBackgroundLocalStorageCacheParent* aActor) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+
+  // Transfer ownership back from IPDL.
+  RefPtr<LocalStorageCacheParent> actor =
+      dont_AddRef(static_cast<LocalStorageCacheParent*>(aActor));
+
+  return true;
+}
+
+PBackgroundStorageParent* AllocPBackgroundStorageParent(
+    const nsAString& aProfilePath, const uint32_t& aPrivateBrowsingId) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  if (NS_WARN_IF(NextGenLocalStorageEnabled()) ||
+      NS_WARN_IF(aPrivateBrowsingId >= kPrivateBrowsingIdCount)) {
+    return nullptr;
+  }
+
+  return new StorageDBParent(aProfilePath, aPrivateBrowsingId);
+}
+
+mozilla::ipc::IPCResult RecvPBackgroundStorageConstructor(
+    PBackgroundStorageParent* aActor, const nsAString& aProfilePath,
+    const uint32_t& aPrivateBrowsingId) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+  MOZ_ASSERT(aPrivateBrowsingId < kPrivateBrowsingIdCount);
+  MOZ_ASSERT(!NextGenLocalStorageEnabled());
+
+  auto* actor = static_cast<StorageDBParent*>(aActor);
+  actor->Init();
+  return IPC_OK();
+}
+
+bool DeallocPBackgroundStorageParent(PBackgroundStorageParent* aActor) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+
+  StorageDBParent* actor = static_cast<StorageDBParent*>(aActor);
+  actor->ReleaseIPDLReference();
+  return true;
+}
+
+PSessionStorageObserverParent* AllocPSessionStorageObserverParent() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  RefPtr<SessionStorageObserverParent> actor =
+      new SessionStorageObserverParent();
+
+  // Transfer ownership to IPDL.
+  return actor.forget().take();
+}
+
+bool RecvPSessionStorageObserverConstructor(
+    PSessionStorageObserverParent* aActor) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aActor);
+
+  return true;
+}
+
+bool DeallocPSessionStorageObserverParent(
+    PSessionStorageObserverParent* aActor) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aActor);
+
+  // Transfer ownership back from IPDL.
+  RefPtr<SessionStorageObserverParent> actor =
+      dont_AddRef(static_cast<SessionStorageObserverParent*>(aActor));
+
+  return true;
+}
+
+already_AddRefed<PBackgroundSessionStorageManagerParent>
+AllocPBackgroundSessionStorageManagerParent(const uint64_t& aTopContextId) {
+  return MakeAndAddRef<SessionStorageManagerParent>(aTopContextId);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/storage/StorageIPC.h b/dom/storage/StorageIPC.h
new file mode 100644
index 0000000000..41d9d88319
--- /dev/null
+++ b/dom/storage/StorageIPC.h
@@ -0,0 +1,617 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_dom_StorageIPC_h
+#define mozilla_dom_StorageIPC_h
+
+#include "LocalStorageCache.h"
+#include "StorageDBThread.h"
+#include "StorageObserver.h"
+
+#include "mozilla/Mutex.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/dom/FlippedOnce.h"
+#include "mozilla/dom/PBackgroundLocalStorageCacheChild.h"
+#include "mozilla/dom/PBackgroundLocalStorageCacheParent.h"
+#include "mozilla/dom/PBackgroundSessionStorageCacheChild.h"
+#include "mozilla/dom/PBackgroundSessionStorageCacheParent.h"
+#include "mozilla/dom/PBackgroundSessionStorageManagerChild.h"
+#include "mozilla/dom/PBackgroundSessionStorageManagerParent.h"
+#include "mozilla/dom/PBackgroundStorageChild.h"
+#include "mozilla/dom/PBackgroundStorageParent.h"
+#include "mozilla/dom/PSessionStorageObserverChild.h"
+#include "mozilla/dom/PSessionStorageObserverParent.h"
+#include "nsTHashSet.h"
+
+namespace mozilla {
+
+class OriginAttributesPattern;
+
+namespace ipc {
+
+class BackgroundChildImpl;
+class PrincipalInfo;
+
+}  // namespace ipc
+
+namespace dom {
+
+class LocalStorageManager;
+class PBackgroundStorageParent;
+class PSessionStorageObserverParent;
+class SessionStorageCache;
+class SessionStorageCacheParent;
+class SessionStorageManager;
+class SessionStorageManagerParent;
+class BackgroundSessionStorageManager;
+class SessionStorageObserver;
+
+class LocalStorageCacheChild final : public PBackgroundLocalStorageCacheChild {
+  friend class mozilla::ipc::BackgroundChildImpl;
+  friend class LocalStorageCache;
+  friend class LocalStorageManager;
+
+  // LocalStorageCache effectively owns this instance, although IPC handles its
+  // allocation/deallocation.  When the LocalStorageCache destructor runs, it
+  // will invoke SendDeleteMeInternal() which will trigger both instances to
+  // drop their mutual references and cause IPC to destroy the actor after the
+  // DeleteMe round-trip.
+  LocalStorageCache* MOZ_NON_OWNING_REF mCache;
+
+  NS_DECL_OWNINGTHREAD
+
+ public:
+  void AssertIsOnOwningThread() const {
+    NS_ASSERT_OWNINGTHREAD(LocalStorageCacheChild);
+  }
+
+ private:
+  // Only created by LocalStorageManager.
+  explicit LocalStorageCacheChild(LocalStorageCache* aCache);
+
+  // Only destroyed by mozilla::ipc::BackgroundChildImpl.
+  ~LocalStorageCacheChild();
+
+  // Only called by LocalStorageCache.
+  void SendDeleteMeInternal();
+
+  // IPDL methods are only called by IPDL.
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  mozilla::ipc::IPCResult RecvObserve(const PrincipalInfo& aPrincipalInfo,
+                                      const PrincipalInfo& aCachePrincipalInfo,
+                                      const uint32_t& aPrivateBrowsingId,
+                                      const nsAString& aDocumentURI,
+                                      const nsAString& aKey,
+                                      const nsAString& aOldValue,
+                                      const nsAString& aNewValue) override;
+};
+
+// Child side of the IPC protocol, exposes as DB interface but
+// is responsible to send all requests to the parent process
+// and expects asynchronous answers. Those are then transparently
+// forwarded back to consumers on the child process.
+class StorageDBChild final : public PBackgroundStorageChild {
+  class ShutdownObserver;
+
+  virtual ~StorageDBChild();
+
+ public:
+  StorageDBChild(LocalStorageManager* aManager, uint32_t aPrivateBrowsingId);
+
+  static StorageDBChild* Get(uint32_t aPrivateBrowsingId);
+
+  static StorageDBChild* GetOrCreate(uint32_t aPrivateBrowsingId);
+
+  NS_INLINE_DECL_REFCOUNTING(StorageDBChild);
+
+  void AddIPDLReference();
+  void ReleaseIPDLReference();
+
+  virtual nsresult Init();
+  virtual nsresult Shutdown();
+
+  virtual void AsyncPreload(LocalStorageCacheBridge* aCache,
+                            bool aPriority = false);
+  virtual void AsyncGetUsage(StorageUsageBridge* aUsage);
+
+  virtual void SyncPreload(LocalStorageCacheBridge* aCache,
+                           bool aForceSync = false);
+
+  virtual nsresult AsyncAddItem(LocalStorageCacheBridge* aCache,
+                                const nsAString& aKey, const nsAString& aValue);
+  virtual nsresult AsyncUpdateItem(LocalStorageCacheBridge* aCache,
+                                   const nsAString& aKey,
+                                   const nsAString& aValue);
+  virtual nsresult AsyncRemoveItem(LocalStorageCacheBridge* aCache,
+                                   const nsAString& aKey);
+  virtual nsresult AsyncClear(LocalStorageCacheBridge* aCache);
+
+  virtual void AsyncClearAll() {
+    if (mOriginsHavingData) {
+      mOriginsHavingData->Clear(); /* NO-OP on the child process otherwise */
+    }
+  }
+
+  virtual void AsyncClearMatchingOrigin(const nsACString& aOriginNoSuffix) {
+    MOZ_CRASH("Shouldn't be called!");
+  }
+
+  virtual void AsyncClearMatchingOriginAttributes(
+      const OriginAttributesPattern& aPattern) {
+    MOZ_CRASH("Shouldn't be called!");
+  }
+
+  virtual void AsyncFlush() { MOZ_CRASH("Shouldn't be called!"); }
+
+  virtual bool ShouldPreloadOrigin(const nsACString& aOriginNoSuffix);
+
+ private:
+  mozilla::ipc::IPCResult RecvObserve(const nsACString& aTopic,
+                                      const nsAString& aOriginAttributesPattern,
+                                      const nsACString& aOriginScope) override;
+  mozilla::ipc::IPCResult RecvLoadItem(const nsACString& aOriginSuffix,
+                                       const nsACString& aOriginNoSuffix,
+                                       const nsAString& aKey,
+                                       const nsAString& aValue) override;
+  mozilla::ipc::IPCResult RecvLoadDone(const nsACString& aOriginSuffix,
+                                       const nsACString& aOriginNoSuffix,
+                                       const nsresult& aRv) override;
+  mozilla::ipc::IPCResult RecvOriginsHavingData(
+      nsTArray<nsCString>&& aOrigins) override;
+  mozilla::ipc::IPCResult RecvLoadUsage(const nsACString& aOriginNoSuffix,
+                                        const int64_t& aUsage) override;
+  mozilla::ipc::IPCResult RecvError(const nsresult& aRv) override;
+
+  nsTHashSet<nsCString>& OriginsHavingData();
+
+  // Held to get caches to forward answers to.
+  RefPtr<LocalStorageManager> mManager;
+
+  // Origins having data hash, for optimization purposes only
+  UniquePtr<nsTHashSet<nsCString>> mOriginsHavingData;
+
+  // List of caches waiting for preload.  This ensures the contract that
+  // AsyncPreload call references the cache for time of the preload.
+  nsTHashSet<RefPtr<LocalStorageCacheBridge>> mLoadingCaches;
+
+  // Expected to be only 0 or 1.
+  const uint32_t mPrivateBrowsingId;
+
+  // Status of the remote database
+  nsresult mStatus;
+
+  bool mIPCOpen;
+};
+
+class SessionStorageObserverChild final : public PSessionStorageObserverChild {
+  friend class SessionStorageManager;
+  friend class SessionStorageObserver;
+
+  // SessionStorageObserver effectively owns this instance, although IPC handles
+  // its allocation/deallocation.  When the SessionStorageObserver destructor
+  // runs, it will invoke SendDeleteMeInternal() which will trigger both
+  // instances to drop their mutual references and cause IPC to destroy the
+  // actor after the DeleteMe round-trip.
+  SessionStorageObserver* MOZ_NON_OWNING_REF mObserver;
+
+  NS_DECL_OWNINGTHREAD
+
+ public:
+  void AssertIsOnOwningThread() const {
+    NS_ASSERT_OWNINGTHREAD(LocalStorageCacheChild);
+  }
+
+ private:
+  // Only created by SessionStorageManager.
+  explicit SessionStorageObserverChild(SessionStorageObserver* aObserver);
+
+  ~SessionStorageObserverChild();
+
+  // Only called by SessionStorageObserver.
+  void SendDeleteMeInternal();
+
+  // IPDL methods are only called by IPDL.
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  mozilla::ipc::IPCResult RecvObserve(const nsACString& aTopic,
+                                      const nsAString& aOriginAttributesPattern,
+                                      const nsACString& aOriginScope) override;
+};
+
+class SessionStorageCacheChild final
+    : public PBackgroundSessionStorageCacheChild {
+  friend class PBackgroundSessionStorageCacheChild;
+  friend class SessionStorageCache;
+  friend class SessionStorageManager;
+  friend class mozilla::ipc::BackgroundChildImpl;
+
+  // SessionStorageManagerChild effectively owns this instance, although IPC
+  // handles its allocation/deallocation.  When the SessionStorageManager
+  // destructor runs, it will invoke SendDeleteMeInternal() which will trigger
+  // both instances to drop their mutual references and cause IPC to destroy the
+  // actor after the DeleteMe round-trip.
+  SessionStorageCache* MOZ_NON_OWNING_REF mCache;
+
+  NS_INLINE_DECL_REFCOUNTING(mozilla::dom::SessionStorageCacheChild, override)
+
+ public:
+  void AssertIsOnOwningThread() const {
+    NS_ASSERT_OWNINGTHREAD(SesionStoragManagerChild);
+  }
+
+ private:
+  // Only created by SessionStorageManager.
+  explicit SessionStorageCacheChild(SessionStorageCache* aCache);
+
+  // Only destroyed by mozilla::ipc::BackgroundChildImpl.
+  ~SessionStorageCacheChild();
+
+  // Only called by SessionStorageCache.
+  void SendDeleteMeInternal();
+
+  // IPDL methods are only called by IPDL.
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+};
+
+class SessionStorageManagerChild final
+    : public PBackgroundSessionStorageManagerChild {
+  friend class PBackgroundSessionStorageManagerChild;
+  friend class SessionStorage;
+  friend class SessionStorageManager;
+  friend class mozilla::ipc::BackgroundChildImpl;
+
+  // SessionStorageManager effectively owns this instance, although IPC handles
+  // its allocation/deallocation.  When the SessionStorageManager destructor
+  // runs, it will invoke SendDeleteMeInternal() which will trigger both
+  // instances to drop their mutual references and cause IPC to destroy the
+  // actor after the DeleteMe round-trip.
+  SessionStorageManager* MOZ_NON_OWNING_REF mSSManager;
+
+  NS_INLINE_DECL_REFCOUNTING(mozilla::dom::SessionStorageManagerChild, override)
+
+ public:
+  void AssertIsOnOwningThread() const {
+    NS_ASSERT_OWNINGTHREAD(SesionStoragManagerChild);
+  }
+
+ private:
+  // Only created by SessionStorage.
+  explicit SessionStorageManagerChild(SessionStorageManager* aSSManager);
+
+  // Only destroyed by mozilla::ipc::BackgroundChildImpl.
+  ~SessionStorageManagerChild();
+
+  // Only called by SessionStorageManager.
+  void SendDeleteMeInternal();
+
+  // IPDL methods are only called by IPDL.
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  mozilla::ipc::IPCResult RecvClearStoragesForOrigin(
+      const nsACString& aOriginAttrs, const nsACString& aOriginKey) override;
+};
+
+class LocalStorageCacheParent final
+    : public PBackgroundLocalStorageCacheParent {
+  const PrincipalInfo mPrincipalInfo;
+  const nsCString mOriginKey;
+  uint32_t mPrivateBrowsingId;
+  bool mActorDestroyed;
+
+ public:
+  // Created in AllocPBackgroundLocalStorageCacheParent.
+  LocalStorageCacheParent(const mozilla::ipc::PrincipalInfo& aPrincipalInfo,
+                          const nsACString& aOriginKey,
+                          uint32_t aPrivateBrowsingId);
+
+  NS_INLINE_DECL_REFCOUNTING(mozilla::dom::LocalStorageCacheParent)
+
+  const PrincipalInfo& PrincipalInfo() const { return mPrincipalInfo; }
+
+ private:
+  // Reference counted.
+  ~LocalStorageCacheParent();
+
+  // IPDL methods are only called by IPDL.
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  mozilla::ipc::IPCResult RecvDeleteMe() override;
+
+  mozilla::ipc::IPCResult RecvNotify(const nsAString& aDocumentURI,
+                                     const nsAString& aKey,
+                                     const nsAString& aOldValue,
+                                     const nsAString& aNewValue) override;
+};
+
+// Receives async requests from child processes and is responsible
+// to send back responses from the DB thread.  Exposes as a fake
+// LocalStorageCache consumer.
+// Also responsible for forwardning all chrome operation notifications
+// such as cookie cleaning etc to the child process.
+class StorageDBParent final : public PBackgroundStorageParent {
+  class ObserverSink;
+
+  virtual ~StorageDBParent();
+
+ public:
+  StorageDBParent(const nsAString& aProfilePath, uint32_t aPrivateBrowsingId);
+
+  void Init();
+
+  NS_IMETHOD_(MozExternalRefCountType) AddRef(void);
+  NS_IMETHOD_(MozExternalRefCountType) Release(void);
+
+  void AddIPDLReference();
+  void ReleaseIPDLReference();
+
+  bool IPCOpen() { return mIPCOpen; }
+
+ public:
+  // Fake cache class receiving async callbacks from DB thread, sending
+  // them back to appropriate cache object on the child process.
+  class CacheParentBridge : public LocalStorageCacheBridge {
+   public:
+    CacheParentBridge(StorageDBParent* aParentDB,
+                      const nsACString& aOriginSuffix,
+                      const nsACString& aOriginNoSuffix)
+        : mOwningEventTarget(GetCurrentSerialEventTarget()),
+          mParent(aParentDB),
+          mOriginSuffix(aOriginSuffix),
+          mOriginNoSuffix(aOriginNoSuffix),
+          mLoaded(false),
+          mLoadedCount(0) {}
+    virtual ~CacheParentBridge() = default;
+
+    // LocalStorageCacheBridge
+    virtual const nsCString Origin() const override;
+    virtual const nsCString& OriginNoSuffix() const override {
+      return mOriginNoSuffix;
+    }
+    virtual const nsCString& OriginSuffix() const override {
+      return mOriginSuffix;
+    }
+    virtual bool Loaded() override { return mLoaded; }
+    virtual uint32_t LoadedCount() override { return mLoadedCount; }
+
+    virtual bool LoadItem(const nsAString& aKey,
+                          const nsAString& aValue) override;
+    virtual void LoadDone(nsresult aRv) override;
+    virtual void LoadWait() override;
+
+    NS_IMETHOD_(void)
+    Release(void) override;
+
+   private:
+    void Destroy();
+
+    nsCOMPtr<nsISerialEventTarget> mOwningEventTarget;
+    RefPtr<StorageDBParent> mParent;
+    nsCString mOriginSuffix, mOriginNoSuffix;
+    bool mLoaded;
+    uint32_t mLoadedCount;
+  };
+
+  // Fake usage class receiving async callbacks from DB thread
+  class UsageParentBridge : public StorageUsageBridge {
+   public:
+    UsageParentBridge(StorageDBParent* aParentDB,
+                      const nsACString& aOriginScope)
+        : mOwningEventTarget(GetCurrentSerialEventTarget()),
+          mParent(aParentDB),
+          mOriginScope(aOriginScope) {}
+    virtual ~UsageParentBridge() = default;
+
+    // StorageUsageBridge
+    virtual const nsCString& OriginScope() override { return mOriginScope; }
+    virtual void LoadUsage(const int64_t usage) override;
+
+    NS_IMETHOD_(MozExternalRefCountType)
+    Release(void) override;
+
+   private:
+    void Destroy();
+
+    nsCOMPtr<nsISerialEventTarget> mOwningEventTarget;
+    RefPtr<StorageDBParent> mParent;
+    nsCString mOriginScope;
+  };
+
+ private:
+  // IPC
+  virtual void ActorDestroy(ActorDestroyReason aWhy) override;
+  mozilla::ipc::IPCResult RecvDeleteMe() override;
+
+  mozilla::ipc::IPCResult RecvAsyncPreload(const nsACString& aOriginSuffix,
+                                           const nsACString& aOriginNoSuffix,
+                                           const bool& aPriority) override;
+  mozilla::ipc::IPCResult RecvPreload(const nsACString& aOriginSuffix,
+                                      const nsACString& aOriginNoSuffix,
+                                      const uint32_t& aAlreadyLoadedCount,
+                                      nsTArray<nsString>* aKeys,
+                                      nsTArray<nsString>* aValues,
+                                      nsresult* aRv) override;
+  mozilla::ipc::IPCResult RecvAsyncGetUsage(
+      const nsACString& aOriginNoSuffix) override;
+  mozilla::ipc::IPCResult RecvAsyncAddItem(const nsACString& aOriginSuffix,
+                                           const nsACString& aOriginNoSuffix,
+                                           const nsAString& aKey,
+                                           const nsAString& aValue) override;
+  mozilla::ipc::IPCResult RecvAsyncUpdateItem(const nsACString& aOriginSuffix,
+                                              const nsACString& aOriginNoSuffix,
+                                              const nsAString& aKey,
+                                              const nsAString& aValue) override;
+  mozilla::ipc::IPCResult RecvAsyncRemoveItem(const nsACString& aOriginSuffix,
+                                              const nsACString& aOriginNoSuffix,
+                                              const nsAString& aKey) override;
+  mozilla::ipc::IPCResult RecvAsyncClear(
+      const nsACString& aOriginSuffix,
+      const nsACString& aOriginNoSuffix) override;
+  mozilla::ipc::IPCResult RecvAsyncFlush() override;
+
+  mozilla::ipc::IPCResult RecvStartup() override;
+  mozilla::ipc::IPCResult RecvClearAll() override;
+  mozilla::ipc::IPCResult RecvClearMatchingOrigin(
+      const nsACString& aOriginNoSuffix) override;
+  mozilla::ipc::IPCResult RecvClearMatchingOriginAttributes(
+      const OriginAttributesPattern& aPattern) override;
+
+  void Observe(const nsACString& aTopic, const nsAString& aOriginAttrPattern,
+               const nsACString& aOriginScope);
+
+ private:
+  CacheParentBridge* NewCache(const nsACString& aOriginSuffix,
+                              const nsACString& aOriginNoSuffix);
+
+  RefPtr<ObserverSink> mObserverSink;
+
+  // A hack to deal with deadlock between the parent process main thread and
+  // background thread when invoking StorageDBThread::GetOrCreate because it
+  // cannot safely perform a synchronous dispatch back to the main thread
+  // (because we are already synchronously doing things on the stack).
+  // Populated for the same process actors, empty for other process actors.
+  nsString mProfilePath;
+
+  // Expected to be only 0 or 1.
+  const uint32_t mPrivateBrowsingId;
+
+  ThreadSafeAutoRefCnt mRefCnt;
+  NS_DECL_OWNINGTHREAD
+
+  // True when IPC channel is open and Send*() methods are OK to use.
+  bool mIPCOpen;
+};
+
+class SessionStorageObserverParent final : public PSessionStorageObserverParent,
+                                           public StorageObserverSink {
+  bool mActorDestroyed;
+
+ public:
+  // Created in AllocPSessionStorageObserverParent.
+  SessionStorageObserverParent();
+
+  NS_INLINE_DECL_REFCOUNTING(mozilla::dom::SessionStorageObserverParent)
+
+ private:
+  // Reference counted.
+  ~SessionStorageObserverParent();
+
+  // IPDL methods are only called by IPDL.
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  mozilla::ipc::IPCResult RecvDeleteMe() override;
+
+  // StorageObserverSink
+  nsresult Observe(const char* aTopic, const nsAString& aOriginAttrPattern,
+                   const nsACString& aOriginScope) override;
+};
+
+class SessionStorageCacheParent final
+    : public PBackgroundSessionStorageCacheParent {
+  friend class PBackgroundSessionStorageCacheParent;
+  const PrincipalInfo mPrincipalInfo;
+  const nsCString mOriginKey;
+
+  RefPtr<SessionStorageManagerParent> mManagerActor;
+  FlippedOnce<false> mLoadReceived;
+
+ public:
+  SessionStorageCacheParent(const PrincipalInfo& aPrincipalInfo,
+                            const nsACString& aOriginKey,
+                            SessionStorageManagerParent* aActor);
+
+  NS_INLINE_DECL_REFCOUNTING(mozilla::dom::SessionStorageCacheParent, override)
+
+  const PrincipalInfo& PrincipalInfo() const { return mPrincipalInfo; }
+  const nsACString& OriginKey() const { return mOriginKey; }
+
+ private:
+  ~SessionStorageCacheParent();
+
+  // IPDL methods are only called by IPDL.
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  mozilla::ipc::IPCResult RecvLoad(nsTArray<SSSetItemInfo>* aData) override;
+
+  mozilla::ipc::IPCResult RecvCheckpoint(
+      nsTArray<SSWriteInfo>&& aWriteInfos) override;
+
+  mozilla::ipc::IPCResult RecvDeleteMe() override;
+};
+
+class SessionStorageManagerParent final
+    : public PBackgroundSessionStorageManagerParent {
+  friend class PBackgroundSessionStorageManagerParent;
+
+  RefPtr<BackgroundSessionStorageManager> mBackgroundManager;
+
+ public:
+  explicit SessionStorageManagerParent(uint64_t aTopContextId);
+
+  NS_INLINE_DECL_REFCOUNTING(mozilla::dom::SessionStorageManagerParent,
+                             override)
+
+  already_AddRefed<PBackgroundSessionStorageCacheParent>
+  AllocPBackgroundSessionStorageCacheParent(
+      const PrincipalInfo& aPrincipalInfo,
+      const nsACString& aOriginKey) override;
+
+  BackgroundSessionStorageManager* GetManager() const;
+
+  mozilla::ipc::IPCResult RecvClearStorages(
+      const OriginAttributesPattern& aPattern,
+      const nsACString& aOriginScope) override;
+
+ private:
+  ~SessionStorageManagerParent();
+
+  // IPDL methods are only called by IPDL.
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  mozilla::ipc::IPCResult RecvDeleteMe() override;
+};
+
+PBackgroundLocalStorageCacheParent* AllocPBackgroundLocalStorageCacheParent(
+    const mozilla::ipc::PrincipalInfo& aPrincipalInfo,
+    const nsACString& aOriginKey, const uint32_t& aPrivateBrowsingId);
+
+mozilla::ipc::IPCResult RecvPBackgroundLocalStorageCacheConstructor(
+    mozilla::ipc::PBackgroundParent* aBackgroundActor,
+    PBackgroundLocalStorageCacheParent* aActor,
+    const mozilla::ipc::PrincipalInfo& aPrincipalInfo,
+    const nsACString& aOriginKey, const uint32_t& aPrivateBrowsingId);
+
+bool DeallocPBackgroundLocalStorageCacheParent(
+    PBackgroundLocalStorageCacheParent* aActor);
+
+PBackgroundStorageParent* AllocPBackgroundStorageParent(
+    const nsAString& aProfilePath, const uint32_t& aPrivateBrowsingId);
+
+mozilla::ipc::IPCResult RecvPBackgroundStorageConstructor(
+    PBackgroundStorageParent* aActor, const nsAString& aProfilePath,
+    const uint32_t& aPrivateBrowsingId);
+
+bool DeallocPBackgroundStorageParent(PBackgroundStorageParent* aActor);
+
+PSessionStorageObserverParent* AllocPSessionStorageObserverParent();
+
+bool RecvPSessionStorageObserverConstructor(
+    PSessionStorageObserverParent* aActor);
+
+bool DeallocPSessionStorageObserverParent(
+    PSessionStorageObserverParent* aActor);
+
+already_AddRefed<PBackgroundSessionStorageCacheParent>
+AllocPBackgroundSessionStorageCacheParent(
+    const mozilla::ipc::PrincipalInfo& aPrincipalInfo,
+    const nsACString& aOriginKey);
+
+already_AddRefed<PBackgroundSessionStorageManagerParent>
+AllocPBackgroundSessionStorageManagerParent(const uint64_t& aTopContextId);
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_StorageIPC_h
diff --git a/dom/storage/StorageNotifierService.cpp b/dom/storage/StorageNotifierService.cpp
new file mode 100644
index 0000000000..57b1ef6bc3
--- /dev/null
+++ b/dom/storage/StorageNotifierService.cpp
@@ -0,0 +1,129 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "StorageNotifierService.h"
+#include "StorageUtils.h"
+#include "mozilla/dom/StorageEvent.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/StaticPtr.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla::dom {
+
+namespace {
+
+// This boolean is used to avoid the creation of the service after been
+// distroyed on shutdown.
+bool gStorageShuttingDown = false;
+
+StaticRefPtr<StorageNotifierService> gStorageNotifierService;
+
+}  // namespace
+
+/* static */
+StorageNotifierService* StorageNotifierService::GetOrCreate() {
+  MOZ_ASSERT(NS_IsMainThread());
+  if (!gStorageNotifierService && !gStorageShuttingDown) {
+    gStorageNotifierService = new StorageNotifierService();
+    ClearOnShutdown(&gStorageNotifierService);
+  }
+
+  return gStorageNotifierService;
+}
+
+StorageNotifierService::StorageNotifierService() {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!gStorageNotifierService);
+}
+
+StorageNotifierService::~StorageNotifierService() {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!gStorageNotifierService);
+  gStorageShuttingDown = true;
+}
+
+/* static */
+void StorageNotifierService::Broadcast(StorageEvent* aEvent,
+                                       const char16_t* aStorageType,
+                                       bool aPrivateBrowsing,
+                                       bool aImmediateDispatch) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  RefPtr<StorageNotifierService> service = gStorageNotifierService;
+  if (!service) {
+    return;
+  }
+
+  RefPtr<StorageEvent> event = aEvent;
+
+  for (const auto& observer : service->mObservers.ForwardRange()) {
+    // Enforce that the source storage area's private browsing state matches
+    // this window's state.  These flag checks and their maintenance independent
+    // from the principal's OriginAttributes matter because chrome docshells
+    // that are part of private browsing windows can be private browsing without
+    // having their OriginAttributes set (because they have the system
+    // principal).
+    if (aPrivateBrowsing != observer->IsPrivateBrowsing()) {
+      continue;
+    }
+
+    // No reasons to continue if the principal of the event doesn't match with
+    // the window's one.
+    if (!StorageUtils::PrincipalsEqual(
+            aEvent->GetPrincipal(), observer->GetEffectiveStoragePrincipal())) {
+      continue;
+    }
+
+    const auto pinnedObserver = observer;
+
+    RefPtr<Runnable> r = NS_NewRunnableFunction(
+        "StorageNotifierService::Broadcast",
+        [pinnedObserver, event, aStorageType, aPrivateBrowsing,
+         aImmediateDispatch]() {
+          // Check principals again. EffectiveStoragePrincipal may be changed
+          // when relaxed.
+          if (!aImmediateDispatch &&
+              !StorageUtils::PrincipalsEqual(
+                  event->GetPrincipal(),
+                  pinnedObserver->GetEffectiveStoragePrincipal())) {
+            return;
+          }
+
+          pinnedObserver->ObserveStorageNotification(event, aStorageType,
+                                                     aPrivateBrowsing);
+        });
+
+    if (aImmediateDispatch) {
+      r->Run();
+    } else {
+      nsCOMPtr<nsIEventTarget> et = pinnedObserver->GetEventTarget();
+      if (et) {
+        et->Dispatch(r.forget());
+      }
+    }
+  }
+}
+
+void StorageNotifierService::Register(StorageNotificationObserver* aObserver) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aObserver);
+  MOZ_ASSERT(!mObservers.Contains(aObserver));
+
+  mObservers.AppendElement(aObserver);
+}
+
+void StorageNotifierService::Unregister(
+    StorageNotificationObserver* aObserver) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aObserver);
+
+  // No assertion about mObservers containing aObserver because window calls
+  // this method multiple times.
+
+  mObservers.RemoveElement(aObserver);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/storage/StorageNotifierService.h b/dom/storage/StorageNotifierService.h
new file mode 100644
index 0000000000..9568f4b259
--- /dev/null
+++ b/dom/storage/StorageNotifierService.h
@@ -0,0 +1,76 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_dom_StorageNotifierService_h
+#define mozilla_dom_StorageNotifierService_h
+
+#include "nsISupportsImpl.h"
+#include "nsTObserverArray.h"
+
+class nsIEventTarget;
+class nsIPrincipal;
+class nsPIDOMWindowInner;
+
+namespace mozilla::dom {
+
+class StorageEvent;
+
+/**
+ * Enables the StorageNotifierService to check whether an observer is interested
+ * in receiving events for the given principal before calling the method, an
+ * optimization refactoring.
+ *
+ * Expected to only be implemented by nsGlobalWindowObserver or its succesor.
+ */
+class StorageNotificationObserver {
+ public:
+  NS_INLINE_DECL_PURE_VIRTUAL_REFCOUNTING
+
+  virtual void ObserveStorageNotification(StorageEvent* aEvent,
+                                          const char16_t* aStorageType,
+                                          bool aPrivateBrowsing) = 0;
+
+  virtual bool IsPrivateBrowsing() const = 0;
+
+  virtual nsIPrincipal* GetEffectiveCookiePrincipal() const = 0;
+
+  virtual nsIPrincipal* GetEffectiveStoragePrincipal() const = 0;
+
+  virtual nsIEventTarget* GetEventTarget() const = 0;
+};
+
+/**
+ * A specialized version of the observer service that uses the custom
+ * StorageNotificationObserver so that principal checks can happen in this class
+ * rather than in the nsIObserver::observe method where they used to happen.
+ *
+ * The only expected consumers are nsGlobalWindowInner instances via their
+ * nsGlobalWindowObserver helper that avoids being able to use the window as an
+ * nsIObserver.
+ */
+class StorageNotifierService final {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(StorageNotifierService)
+
+  static StorageNotifierService* GetOrCreate();
+
+  static void Broadcast(StorageEvent* aEvent, const char16_t* aStorageType,
+                        bool aPrivateBrowsing, bool aImmediateDispatch);
+
+  void Register(StorageNotificationObserver* aObserver);
+
+  void Unregister(StorageNotificationObserver* aObserver);
+
+ private:
+  StorageNotifierService();
+  ~StorageNotifierService();
+
+  nsTObserverArray<RefPtr<StorageNotificationObserver>> mObservers;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_StorageNotifierService_h
diff --git a/dom/storage/StorageObserver.cpp b/dom/storage/StorageObserver.cpp
new file mode 100644
index 0000000000..bdad1a5ea2
--- /dev/null
+++ b/dom/storage/StorageObserver.cpp
@@ -0,0 +1,532 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "StorageObserver.h"
+
+#include "LocalStorageCache.h"
+#include "StorageCommon.h"
+#include "StorageDBThread.h"
+#include "StorageIPC.h"
+#include "StorageUtils.h"
+
+#include "mozilla/BasePrincipal.h"
+#include "nsIObserverService.h"
+#include "nsIURI.h"
+#include "nsIPermission.h"
+#include "nsIIDNService.h"
+#include "nsICookiePermission.h"
+
+#include "nsPrintfCString.h"
+#include "nsXULAppAPI.h"
+#include "nsEscape.h"
+#include "nsNetCID.h"
+#include "mozilla/dom/LocalStorageCommon.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/Services.h"
+#include "mozilla/SpinEventLoopUntil.h"
+#include "nsServiceManagerUtils.h"
+
+namespace mozilla::dom {
+
+using namespace StorageUtils;
+
+static const char kStartupTopic[] = "sessionstore-windows-restored";
+static const uint32_t kStartupDelay = 0;
+
+const char kTestingPref[] = "dom.storage.testing";
+
+constexpr auto kPrivateBrowsingPattern = u"{ \"privateBrowsingId\": 1 }"_ns;
+
+NS_IMPL_ISUPPORTS(StorageObserver, nsIObserver, nsINamed,
+                  nsISupportsWeakReference)
+
+StorageObserver* StorageObserver::sSelf = nullptr;
+
+// static
+nsresult StorageObserver::Init() {
+  static_assert(kPrivateBrowsingIdCount * sizeof(mBackgroundThread[0]) ==
+                sizeof(mBackgroundThread));
+  if (sSelf) {
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  if (!obs) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  sSelf = new StorageObserver();
+  NS_ADDREF(sSelf);
+
+  // Chrome clear operations.
+  obs->AddObserver(sSelf, kStartupTopic, true);
+  obs->AddObserver(sSelf, "cookie-changed", true);
+  obs->AddObserver(sSelf, "perm-changed", true);
+  obs->AddObserver(sSelf, "last-pb-context-exited", true);
+  obs->AddObserver(sSelf, "clear-origin-attributes-data", true);
+  obs->AddObserver(sSelf, "dom-storage:clear-origin-attributes-data", true);
+  obs->AddObserver(sSelf, "extension:purge-localStorage", true);
+  obs->AddObserver(sSelf, "browser:purge-sessionStorage", true);
+
+  // Shutdown
+  obs->AddObserver(sSelf, "profile-after-change", true);
+  if (XRE_IsParentProcess()) {
+    obs->AddObserver(sSelf, "profile-before-change", true);
+  }
+
+  // Testing
+#ifdef DOM_STORAGE_TESTS
+  Preferences::RegisterCallbackAndCall(TestingPrefChanged, kTestingPref);
+#endif
+
+  return NS_OK;
+}
+
+// static
+nsresult StorageObserver::Shutdown() {
+  AssertIsOnMainThread();
+
+  if (!sSelf) {
+    return NS_ERROR_NOT_INITIALIZED;  // Is this always an error?
+  }
+
+  sSelf->mSinks.Clear();
+
+  NS_RELEASE(sSelf);
+  return NS_OK;
+}
+
+// static
+void StorageObserver::TestingPrefChanged(const char* aPrefName,
+                                         void* aClosure) {
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  if (!obs || !sSelf) {
+    return;
+  }
+
+  if (Preferences::GetBool(kTestingPref)) {
+    obs->AddObserver(sSelf, "domstorage-test-flush-force", true);
+    if (XRE_IsParentProcess()) {
+      // Only to forward to child process.
+      obs->AddObserver(sSelf, "domstorage-test-flushed", true);
+    }
+    obs->AddObserver(sSelf, "domstorage-test-reload", true);
+  } else {
+    obs->RemoveObserver(sSelf, "domstorage-test-flush-force");
+    if (XRE_IsParentProcess()) {
+      // Only to forward to child process.
+      obs->RemoveObserver(sSelf, "domstorage-test-flushed");
+    }
+    obs->RemoveObserver(sSelf, "domstorage-test-reload");
+  }
+}
+
+void StorageObserver::AddSink(StorageObserverSink* aObs) {
+  AssertIsOnMainThread();
+
+  MOZ_ASSERT(sSelf);
+
+  mSinks.AppendElement(aObs);
+}
+
+void StorageObserver::RemoveSink(StorageObserverSink* aObs) {
+  AssertIsOnMainThread();
+
+  MOZ_ASSERT(sSelf);
+
+  mSinks.RemoveElement(aObs);
+}
+
+void StorageObserver::Notify(const char* aTopic,
+                             const nsAString& aOriginAttributesPattern,
+                             const nsACString& aOriginScope) {
+  AssertIsOnMainThread();
+
+  MOZ_ASSERT(sSelf);
+
+  for (auto sink : mSinks.ForwardRange()) {
+    sink->Observe(aTopic, aOriginAttributesPattern, aOriginScope);
+  }
+}
+
+void StorageObserver::NoteBackgroundThread(const uint32_t aPrivateBrowsingId,
+                                           nsIEventTarget* aBackgroundThread) {
+  MOZ_RELEASE_ASSERT(aPrivateBrowsingId < kPrivateBrowsingIdCount);
+
+  mBackgroundThread[aPrivateBrowsingId] = aBackgroundThread;
+}
+
+nsresult StorageObserver::GetOriginScope(const char16_t* aData,
+                                         nsACString& aOriginScope) {
+  nsresult rv;
+
+  NS_ConvertUTF16toUTF8 domain(aData);
+
+  nsAutoCString convertedDomain;
+  nsCOMPtr<nsIIDNService> converter = do_GetService(NS_IDNSERVICE_CONTRACTID);
+  if (converter) {
+    // Convert the domain name to the ACE format
+    rv = converter->ConvertUTF8toACE(domain, convertedDomain);
+  } else {
+    // In case the IDN service is not available, this is the best we can come
+    // up with!
+    rv = NS_EscapeURL(domain, esc_OnlyNonASCII | esc_AlwaysCopy,
+                      convertedDomain, fallible);
+  }
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  nsCString originScope;
+  rv = CreateReversedDomain(convertedDomain, originScope);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  aOriginScope = originScope;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+StorageObserver::Observe(nsISupports* aSubject, const char* aTopic,
+                         const char16_t* aData) {
+  if (NS_WARN_IF(!sSelf)) {  // Shutdown took place
+    return NS_OK;
+  }
+
+  nsresult rv;
+
+  // Start the thread that opens the database.
+  if (!strcmp(aTopic, kStartupTopic)) {
+    MOZ_ASSERT(XRE_IsParentProcess());
+
+    if (NextGenLocalStorageEnabled()) {
+      return NS_OK;
+    }
+
+    nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+    obs->RemoveObserver(this, kStartupTopic);
+
+    return NS_NewTimerWithObserver(getter_AddRefs(mDBThreadStartDelayTimer),
+                                   this, nsITimer::TYPE_ONE_SHOT,
+                                   kStartupDelay);
+  }
+
+  // Timer callback used to start the database a short timer after startup
+  if (!strcmp(aTopic, NS_TIMER_CALLBACK_TOPIC)) {
+    MOZ_ASSERT(XRE_IsParentProcess());
+    MOZ_ASSERT(!NextGenLocalStorageEnabled());
+
+    nsCOMPtr<nsITimer> timer = do_QueryInterface(aSubject);
+    if (!timer) {
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    if (timer == mDBThreadStartDelayTimer) {
+      mDBThreadStartDelayTimer = nullptr;
+
+      for (const uint32_t id : {0, 1}) {
+        StorageDBChild* storageChild = StorageDBChild::GetOrCreate(id);
+        if (NS_WARN_IF(!storageChild)) {
+          return NS_ERROR_FAILURE;
+        }
+
+        storageChild->SendStartup();
+      }
+    }
+
+    return NS_OK;
+  }
+
+  // Clear everything, caches + database
+  if (!strcmp(aTopic, "cookie-changed")) {
+    if (!u"cleared"_ns.Equals(aData)) {
+      return NS_OK;
+    }
+
+    if (!NextGenLocalStorageEnabled()) {
+      for (const uint32_t id : {0, 1}) {
+        StorageDBChild* storageChild = StorageDBChild::GetOrCreate(id);
+        if (NS_WARN_IF(!storageChild)) {
+          return NS_ERROR_FAILURE;
+        }
+
+        storageChild->AsyncClearAll();
+
+        if (XRE_IsParentProcess()) {
+          storageChild->SendClearAll();
+        }
+      }
+    }
+
+    Notify("cookie-cleared");
+
+    return NS_OK;
+  }
+
+  // Clear from caches everything that has been stored
+  // while in session-only mode
+  if (!strcmp(aTopic, "perm-changed")) {
+    // Check for cookie permission change
+    nsCOMPtr<nsIPermission> perm(do_QueryInterface(aSubject));
+    if (!perm) {
+      return NS_OK;
+    }
+
+    nsAutoCString type;
+    perm->GetType(type);
+    if (type != "cookie"_ns) {
+      return NS_OK;
+    }
+
+    uint32_t cap = 0;
+    perm->GetCapability(&cap);
+    if (!(cap & nsICookiePermission::ACCESS_SESSION) ||
+        !u"deleted"_ns.Equals(nsDependentString(aData))) {
+      return NS_OK;
+    }
+
+    nsCOMPtr<nsIPrincipal> principal;
+    perm->GetPrincipal(getter_AddRefs(principal));
+    if (!principal) {
+      return NS_OK;
+    }
+
+    nsAutoCString originSuffix;
+    BasePrincipal::Cast(principal)->OriginAttributesRef().CreateSuffix(
+        originSuffix);
+
+    nsAutoCString host;
+    principal->GetHost(host);
+    if (host.IsEmpty()) {
+      return NS_OK;
+    }
+
+    nsAutoCString originScope;
+    rv = CreateReversedDomain(host, originScope);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    Notify("session-only-cleared", NS_ConvertUTF8toUTF16(originSuffix),
+           originScope);
+
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "extension:purge-localStorage")) {
+    if (NextGenLocalStorageEnabled()) {
+      return NS_OK;
+    }
+
+    const char topic[] = "extension:purge-localStorage-caches";
+
+    if (aData) {
+      nsCString originScope;
+
+      rv = GetOriginScope(aData, originScope);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+
+      if (XRE_IsParentProcess()) {
+        for (const uint32_t id : {0, 1}) {
+          StorageDBChild* storageChild = StorageDBChild::GetOrCreate(id);
+          if (NS_WARN_IF(!storageChild)) {
+            return NS_ERROR_FAILURE;
+          }
+
+          storageChild->SendClearMatchingOrigin(originScope);
+        }
+      }
+
+      Notify(topic, u""_ns, originScope);
+    } else {
+      for (const uint32_t id : {0, 1}) {
+        StorageDBChild* storageChild = StorageDBChild::GetOrCreate(id);
+        if (NS_WARN_IF(!storageChild)) {
+          return NS_ERROR_FAILURE;
+        }
+
+        storageChild->AsyncClearAll();
+
+        if (XRE_IsParentProcess()) {
+          storageChild->SendClearAll();
+        }
+      }
+
+      Notify(topic);
+    }
+
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "browser:purge-sessionStorage")) {
+    if (aData) {
+      nsCString originScope;
+      rv = GetOriginScope(aData, originScope);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+
+      Notify(aTopic, u""_ns, originScope);
+    } else {
+      Notify(aTopic, u""_ns, ""_ns);
+    }
+
+    return NS_OK;
+  }
+
+  // Clear all private-browsing caches
+  if (!strcmp(aTopic, "last-pb-context-exited")) {
+    if (NextGenLocalStorageEnabled()) {
+      return NS_OK;
+    }
+
+    // We get the notification in both processes (parent and content), but the
+    // clearing of the in-memory database should be triggered from the parent
+    // process only to avoid creation of redundant clearing operations.
+    // Also, if we create a new StorageDBChild instance late during content
+    // process shutdown, then it might be leaked in debug builds because it
+    // could happen that there is no chance to properly destroy it.
+    if (XRE_IsParentProcess()) {
+      // This doesn't use a loop with privateBrowsingId 0 and 1, since we only
+      // need to clear the in-memory database which is represented by
+      // privateBrowsingId 1.
+      static const uint32_t id = 1;
+
+      StorageDBChild* storageChild = StorageDBChild::GetOrCreate(id);
+      if (NS_WARN_IF(!storageChild)) {
+        return NS_ERROR_FAILURE;
+      }
+
+      OriginAttributesPattern pattern;
+      if (!pattern.Init(kPrivateBrowsingPattern)) {
+        NS_ERROR("Cannot parse origin attributes pattern");
+        return NS_ERROR_FAILURE;
+      }
+
+      storageChild->SendClearMatchingOriginAttributes(pattern);
+    }
+
+    Notify("private-browsing-data-cleared", kPrivateBrowsingPattern);
+
+    return NS_OK;
+  }
+
+  // Clear data of the origins whose prefixes will match the suffix.
+  if (!strcmp(aTopic, "clear-origin-attributes-data") ||
+      !strcmp(aTopic, "dom-storage:clear-origin-attributes-data")) {
+    MOZ_ASSERT(XRE_IsParentProcess());
+
+    OriginAttributesPattern pattern;
+    if (!pattern.Init(nsDependentString(aData))) {
+      NS_ERROR("Cannot parse origin attributes pattern");
+      return NS_ERROR_FAILURE;
+    }
+
+    if (NextGenLocalStorageEnabled()) {
+      Notify("session-storage:clear-origin-attributes-data",
+             nsDependentString(aData));
+      return NS_OK;
+    }
+
+    for (const uint32_t id : {0, 1}) {
+      StorageDBChild* storageChild = StorageDBChild::GetOrCreate(id);
+      if (NS_WARN_IF(!storageChild)) {
+        return NS_ERROR_FAILURE;
+      }
+
+      storageChild->SendClearMatchingOriginAttributes(pattern);
+    }
+
+    Notify(aTopic, nsDependentString(aData));
+
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "profile-after-change")) {
+    Notify("profile-change");
+
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "profile-before-change")) {
+    MOZ_ASSERT(XRE_IsParentProcess());
+
+    if (NextGenLocalStorageEnabled()) {
+      return NS_OK;
+    }
+
+    for (const uint32_t id : {0, 1}) {
+      if (mBackgroundThread[id]) {
+        bool done = false;
+
+        RefPtr<StorageDBThread::ShutdownRunnable> shutdownRunnable =
+            new StorageDBThread::ShutdownRunnable(id, done);
+        MOZ_ALWAYS_SUCCEEDS(mBackgroundThread[id]->Dispatch(
+            shutdownRunnable, NS_DISPATCH_NORMAL));
+
+        MOZ_ALWAYS_TRUE(SpinEventLoopUntil(
+            "StorageObserver::Observe profile-before-change"_ns,
+            [&]() { return done; }));
+
+        mBackgroundThread[id] = nullptr;
+      }
+    }
+
+    return NS_OK;
+  }
+
+#ifdef DOM_STORAGE_TESTS
+  if (!strcmp(aTopic, "domstorage-test-flush-force")) {
+    if (NextGenLocalStorageEnabled()) {
+      return NS_OK;
+    }
+
+    for (const uint32_t id : {0, 1}) {
+      StorageDBChild* storageChild = StorageDBChild::GetOrCreate(id);
+      if (NS_WARN_IF(!storageChild)) {
+        return NS_ERROR_FAILURE;
+      }
+
+      storageChild->SendAsyncFlush();
+    }
+
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "domstorage-test-flushed")) {
+    if (NextGenLocalStorageEnabled()) {
+      return NS_OK;
+    }
+
+    // Only used to propagate to IPC children
+    Notify("test-flushed");
+
+    return NS_OK;
+  }
+
+  if (!strcmp(aTopic, "domstorage-test-reload")) {
+    if (NextGenLocalStorageEnabled()) {
+      return NS_OK;
+    }
+
+    Notify("test-reload");
+
+    return NS_OK;
+  }
+#endif
+
+  NS_ERROR("Unexpected topic");
+  return NS_ERROR_UNEXPECTED;
+}
+
+NS_IMETHODIMP
+StorageObserver::GetName(nsACString& aName) {
+  aName.AssignLiteral("StorageObserver");
+  return NS_OK;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/storage/StorageObserver.h b/dom/storage/StorageObserver.h
new file mode 100644
index 0000000000..df2b87b2e4
--- /dev/null
+++ b/dom/storage/StorageObserver.h
@@ -0,0 +1,79 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_dom_StorageObserver_h
+#define mozilla_dom_StorageObserver_h
+
+#include "mozilla/dom/quota/CheckedUnsafePtr.h"
+#include "nsINamed.h"
+#include "nsIObserver.h"
+#include "nsITimer.h"
+#include "nsWeakReference.h"
+#include "nsTObserverArray.h"
+#include "nsString.h"
+
+namespace mozilla::dom {
+
+class StorageObserver;
+
+// Main-thread interface implemented by legacy LocalStorageManager and current
+// SessionStorageManager for direct consumption. Also implemented by legacy
+// StorageDBParent and current SessionStorageObserverParent for propagation to
+// content processes.
+class StorageObserverSink
+    : public SupportsCheckedUnsafePtr<CheckIf<DiagnosticAssertEnabled>> {
+ public:
+  virtual ~StorageObserverSink() = default;
+
+ private:
+  friend class StorageObserver;
+  virtual nsresult Observe(const char* aTopic,
+                           const nsAString& aOriginAttributesPattern,
+                           const nsACString& aOriginScope) = 0;
+};
+
+// Statically (through layout statics) initialized observer receiving and
+// processing chrome clearing notifications, such as cookie deletion etc.
+class StorageObserver : public nsIObserver,
+                        public nsINamed,
+                        public nsSupportsWeakReference {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+  NS_DECL_NSINAMED
+
+  static nsresult Init();
+  static nsresult Shutdown();
+  static StorageObserver* Self() { return sSelf; }
+
+  void AddSink(StorageObserverSink* aObs);
+  void RemoveSink(StorageObserverSink* aObs);
+  void Notify(const char* aTopic,
+              const nsAString& aOriginAttributesPattern = u""_ns,
+              const nsACString& aOriginScope = ""_ns);
+
+  void NoteBackgroundThread(uint32_t aPrivateBrowsingId,
+                            nsIEventTarget* aBackgroundThread);
+
+ private:
+  virtual ~StorageObserver() = default;
+
+  nsresult GetOriginScope(const char16_t* aData, nsACString& aOriginScope);
+
+  static void TestingPrefChanged(const char* aPrefName, void* aClosure);
+
+  static StorageObserver* sSelf;
+
+  nsCOMPtr<nsIEventTarget> mBackgroundThread[2];
+
+  // Weak references
+  nsTObserverArray<CheckedUnsafePtr<StorageObserverSink>> mSinks;
+  nsCOMPtr<nsITimer> mDBThreadStartDelayTimer;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_StorageObserver_h
diff --git a/dom/storage/StorageUtils.cpp b/dom/storage/StorageUtils.cpp
new file mode 100644
index 0000000000..39a69c3f08
--- /dev/null
+++ b/dom/storage/StorageUtils.cpp
@@ -0,0 +1,110 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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/. */
+
+#include "nsIURL.h"
+#include "StorageUtils.h"
+
+#include "mozilla/OriginAttributes.h"
+#include "nsDebug.h"
+#include "nsIPrincipal.h"
+#include "nsIURI.h"
+#include "nsNetUtil.h"
+#include "nsPrintfCString.h"
+
+namespace mozilla::dom::StorageUtils {
+
+bool PrincipalsEqual(nsIPrincipal* aObjectPrincipal,
+                     nsIPrincipal* aSubjectPrincipal) {
+  if (!aSubjectPrincipal) {
+    return true;
+  }
+
+  if (!aObjectPrincipal) {
+    return false;
+  }
+
+  return aSubjectPrincipal->Equals(aObjectPrincipal);
+}
+
+void ReverseString(const nsACString& aSource, nsACString& aResult) {
+  nsACString::const_iterator sourceBegin, sourceEnd;
+  aSource.BeginReading(sourceBegin);
+  aSource.EndReading(sourceEnd);
+
+  aResult.SetLength(aSource.Length());
+  auto destEnd = aResult.EndWriting();
+
+  while (sourceBegin != sourceEnd) {
+    *(--destEnd) = *sourceBegin;
+    ++sourceBegin;
+  }
+}
+
+nsresult CreateReversedDomain(const nsACString& aAsciiDomain,
+                              nsACString& aKey) {
+  if (aAsciiDomain.IsEmpty()) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  ReverseString(aAsciiDomain, aKey);
+
+  aKey.Append('.');
+  return NS_OK;
+}
+
+// This is only a compatibility code for schema version 0.  Returns the 'scope'
+// key in the schema version 0 format for the scope column.
+nsCString Scheme0Scope(const nsACString& aOriginSuffix,
+                       const nsACString& aOriginNoSuffix) {
+  nsCString result;
+
+  OriginAttributes oa;
+  if (!aOriginSuffix.IsEmpty()) {
+    DebugOnly<bool> success = oa.PopulateFromSuffix(aOriginSuffix);
+    MOZ_ASSERT(success);
+  }
+
+  if (oa.mInIsolatedMozBrowser) {
+    result.AppendInt(0);  // This is the appId to be removed.
+    result.Append(':');
+    result.Append(oa.mInIsolatedMozBrowser ? 't' : 'f');
+    result.Append(':');
+  }
+
+  // If there is more than just appid and/or inbrowser stored in origin
+  // attributes, put it to the schema 0 scope as well.  We must do that
+  // to keep the scope column unique (same resolution as schema 1 has
+  // with originAttributes and originKey columns) so that switch between
+  // schema 1 and 0 always works in both ways.
+  nsAutoCString remaining;
+  oa.mInIsolatedMozBrowser = false;
+  oa.CreateSuffix(remaining);
+  if (!remaining.IsEmpty()) {
+    MOZ_ASSERT(!aOriginSuffix.IsEmpty());
+
+    if (result.IsEmpty()) {
+      // Must contain the old prefix, otherwise we won't search for the whole
+      // origin attributes suffix.
+      result.AppendLiteral("0:f:");
+    }
+
+    // Append the whole origin attributes suffix despite we have already stored
+    // appid and inbrowser.  We are only looking for it when the scope string
+    // starts with "$appid:$inbrowser:" (with whatever valid values).
+    //
+    // The OriginAttributes suffix is a string in a form like:
+    // "^addonId=101&userContextId=5" and it's ensured it always starts with '^'
+    // and never contains ':'.  See OriginAttributes::CreateSuffix.
+    result.Append(aOriginSuffix);
+    result.Append(':');
+  }
+
+  result.Append(aOriginNoSuffix);
+
+  return result;
+}
+
+}  // namespace mozilla::dom::StorageUtils
diff --git a/dom/storage/StorageUtils.h b/dom/storage/StorageUtils.h
new file mode 100644
index 0000000000..3a8d7c03a6
--- /dev/null
+++ b/dom/storage/StorageUtils.h
@@ -0,0 +1,28 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 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_dom_StorageUtils_h
+#define mozilla_dom_StorageUtils_h
+
+#include "nsStringFwd.h"
+
+class nsIPrincipal;
+
+namespace mozilla::dom::StorageUtils {
+
+bool PrincipalsEqual(nsIPrincipal* aObjectPrincipal,
+                     nsIPrincipal* aSubjectPrincipal);
+
+void ReverseString(const nsACString& aSource, nsACString& aResult);
+
+nsresult CreateReversedDomain(const nsACString& aAsciiDomain, nsACString& aKey);
+
+nsCString Scheme0Scope(const nsACString& aOriginSuffix,
+                       const nsACString& aOriginNoSuffix);
+
+}  // namespace mozilla::dom::StorageUtils
+
+#endif  // mozilla_dom_StorageUtils_h
diff --git a/dom/storage/components.conf b/dom/storage/components.conf
new file mode 100644
index 0000000000..15b95f6b0f
--- /dev/null
+++ b/dom/storage/components.conf
@@ -0,0 +1,16 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+Classes = [
+    {
+        'js_name': 'sessionStorage',
+        'cid': '{7ec4bc82-5022-4d32-8e98-ffbceadb692c}',
+        'contract_ids': ['@mozilla.org/dom/session-storage-service;1'],
+        'interfaces': ['nsISessionStorageService'],
+        'singleton': True,
+        'type': 'nsISessionStorageService',
+    },
+]
diff --git a/dom/storage/moz.build b/dom/storage/moz.build
new file mode 100644
index 0000000000..963067ced4
--- /dev/null
+++ b/dom/storage/moz.build
@@ -0,0 +1,74 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# 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/.
+
+with Files("**"):
+    BUG_COMPONENT = ("Core", "Storage: localStorage & sessionStorage")
+
+XPIDL_SOURCES += [
+    "nsISessionStorageService.idl",
+]
+
+XPIDL_MODULE = "dom_storage"
+
+EXPORTS.mozilla.dom += [
+    "BackgroundSessionStorageServiceParent.h",
+    "LocalStorage.h",
+    "LocalStorageManager.h",
+    "PartitionedLocalStorage.h",
+    "SessionStorageManager.h",
+    "SessionStorageService.h",
+    "Storage.h",
+    "StorageActivityService.h",
+    "StorageDBUpdater.h",
+    "StorageIPC.h",
+    "StorageNotifierService.h",
+    "StorageObserver.h",
+    "StorageUtils.h",
+]
+
+XPCOM_MANIFESTS += [
+    "components.conf",
+]
+
+UNIFIED_SOURCES += [
+    "BackgroundSessionStorageServiceParent.cpp",
+    "LocalStorage.cpp",
+    "LocalStorageCache.cpp",
+    "LocalStorageManager.cpp",
+    "PartitionedLocalStorage.cpp",
+    "SessionStorage.cpp",
+    "SessionStorageCache.cpp",
+    "SessionStorageManager.cpp",
+    "SessionStorageObserver.cpp",
+    "SessionStorageService.cpp",
+    "Storage.cpp",
+    "StorageActivityService.cpp",
+    "StorageDBThread.cpp",
+    "StorageDBUpdater.cpp",
+    "StorageIPC.cpp",
+    "StorageNotifierService.cpp",
+    "StorageObserver.cpp",
+    "StorageUtils.cpp",
+]
+
+IPDL_SOURCES += [
+    "PBackgroundLocalStorageCache.ipdl",
+    "PBackgroundSessionStorageCache.ipdl",
+    "PBackgroundSessionStorageManager.ipdl",
+    "PBackgroundSessionStorageService.ipdl",
+    "PBackgroundStorage.ipdl",
+    "PSessionStorageObserver.ipdl",
+]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+FINAL_LIBRARY = "xul"
+LOCAL_INCLUDES += [
+    "/dom/base",
+]
+
+if CONFIG["ENABLE_TESTS"]:
+    DEFINES["DOM_STORAGE_TESTS"] = True
diff --git a/dom/storage/nsISessionStorageService.idl b/dom/storage/nsISessionStorageService.idl
new file mode 100644
index 0000000000..743c1ebfaa
--- /dev/null
+++ b/dom/storage/nsISessionStorageService.idl
@@ -0,0 +1,21 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 et sw=2 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/. */
+
+#include "nsISupports.idl"
+
+interface nsIPrincipal;
+
+[scriptable, builtinclass, uuid(3b95dd6c-0293-4e06-baeb-2affaefc9e74)]
+interface nsISessionStorageService : nsISupports
+{
+  /**
+   * Removes all storages stored for the given principal.
+   *
+   * @param aPrincipal
+   *        A principal for the origin whose storages are to be cleared.
+   */
+  void clearStoragesForOrigin(in nsIPrincipal aPrincipal);
+};