Adding upstream version 110.0.1.upstream/110.0.1upstream

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

24 files changed, 6221 insertions, 0 deletions

diff --git a/dom/webbrowserpersist/PWebBrowserPersistDocument.ipdl b/dom/webbrowserpersist/PWebBrowserPersistDocument.ipdl
new file mode 100644
index 0000000000..ee2e50185f
--- /dev/null
+++ b/dom/webbrowserpersist/PWebBrowserPersistDocument.ipdl
@@ -0,0 +1,100 @@
+/* -*- Mode: IDL; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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;
+include protocol PWebBrowserPersistResources;
+include protocol PWebBrowserPersistSerialize;
+
+include PBackgroundSharedTypes;
+include IPCStream;
+include NeckoChannelParams;
+
+include "mozilla/dom/ReferrerInfoUtils.h";
+
+[RefCounted] using class nsIReferrerInfo from "nsIReferrerInfo.h";
+
+namespace mozilla {
+
+// nsIWebBrowserPersistDocument has attributes which can be read
+// synchronously.  To avoid using sync IPC for them, the actor sends
+// this structure from the child to the parent before the parent actor
+// is exposed to XPCOM.
+struct WebBrowserPersistDocumentAttrs {
+  bool isPrivate;
+  nsCString documentURI;
+  nsCString baseURI;
+  nsCString contentType;
+  nsCString characterSet;
+  nsString title;
+  nsIReferrerInfo referrerInfo;
+  CookieJarSettingsArgs cookieJarSettings;
+  nsString contentDisposition;
+  uint32_t sessionHistoryCacheKey;
+  uint32_t persistFlags;
+  PrincipalInfo principal;
+};
+
+// IPDL doesn't have tuples, so this gives the pair of strings from
+// nsIWebBrowserPersistURIMap::getURIMapping a name.
+struct WebBrowserPersistURIMapEntry {
+  nsCString mapFrom;
+  nsCString mapTo;
+};
+
+// nsIWebBrowserPersistURIMap is just copied over IPC as one of these,
+// not proxied, to simplify the protocol.
+struct WebBrowserPersistURIMap {
+  WebBrowserPersistURIMapEntry[] mapURIs;
+  nsCString targetBaseURI;
+};
+
+// This remotes nsIWebBrowserPersistDocument and its visitors.  The
+// lifecycle is a little complicated: the initial document is
+// constructed parent->child, but subdocuments are constructed
+// child->parent and then passed back.  Subdocuments aren't subactors,
+// because that would impose a lifetime relationship that doesn't
+// exist in the XPIDL; instead they're all managed by the enclosing
+// PContent.
+[ManualDealloc]
+protocol PWebBrowserPersistDocument {
+  manager PContent;
+  manages PWebBrowserPersistResources;
+  manages PWebBrowserPersistSerialize;
+
+parent:
+  // The actor isn't exposed to XPCOM until after it gets one of these
+  // two messages; see also the state transition rules.  The message
+  // is either a response to the constructor (if it was parent->child)
+  // or sent after it (if it was child->parent).
+  async Attributes(WebBrowserPersistDocumentAttrs aAttrs,
+                   IPCStream? stream);
+  async InitFailure(nsresult aStatus);
+
+child:
+  async SetPersistFlags(uint32_t aNewFlags);
+  async PWebBrowserPersistResources();
+  async PWebBrowserPersistSerialize(WebBrowserPersistURIMap aMap,
+                                    nsCString aRequestedContentType,
+                                    uint32_t aEncoderFlags,
+                                    uint32_t aWrapColumn);
+  async __delete__();
+
+/*
+state START:
+  recv Attributes goto MAIN;
+  recv InitFailure goto FAILED;
+
+state MAIN:
+  send SetPersistFlags goto MAIN;
+  send PWebBrowserPersistResources goto MAIN;
+  send PWebBrowserPersistSerialize goto MAIN;
+  send __delete__;
+
+state FAILED:
+  send __delete__;
+*/
+};
+
+} // namespace mozilla
diff --git a/dom/webbrowserpersist/PWebBrowserPersistResources.ipdl b/dom/webbrowserpersist/PWebBrowserPersistResources.ipdl
new file mode 100644
index 0000000000..87b880c296
--- /dev/null
+++ b/dom/webbrowserpersist/PWebBrowserPersistResources.ipdl
@@ -0,0 +1,32 @@
+/* -*- Mode: IDL; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 PWebBrowserPersistDocument;
+
+using mozilla::dom::MaybeDiscardedBrowsingContext from "mozilla/dom/BrowsingContext.h";
+using nsContentPolicyType from "nsIContentPolicy.h";
+
+namespace mozilla {
+
+// == nsIWebBrowserPersistResourceVisitor
+[ManualDealloc, ChildImpl=virtual, ParentImpl=virtual]
+protocol PWebBrowserPersistResources {
+  manager PWebBrowserPersistDocument;
+
+parent:
+  async VisitResource(nsCString aURI, nsContentPolicyType aContentPolicyType);
+
+  // The actor sent here is in the START state; the parent-side
+  // receiver will have to wait for it to enter the MAIN state
+  // before exposing it with a visitDocument call.
+  async VisitDocument(PWebBrowserPersistDocument aSubDocument);
+
+  async VisitBrowsingContext(MaybeDiscardedBrowsingContext aContext);
+
+  // This reflects the endVisit method.
+  async __delete__(nsresult aStatus);
+};
+
+} // namespace mozilla
diff --git a/dom/webbrowserpersist/PWebBrowserPersistSerialize.ipdl b/dom/webbrowserpersist/PWebBrowserPersistSerialize.ipdl
new file mode 100644
index 0000000000..11fbe530c0
--- /dev/null
+++ b/dom/webbrowserpersist/PWebBrowserPersistSerialize.ipdl
@@ -0,0 +1,30 @@
+/* -*- Mode: IDL; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 PWebBrowserPersistDocument;
+
+namespace mozilla {
+
+// This actor represents both an nsIWebBrowserPersistWriteCompletion
+// and the nsIOutputStream passed with it to the writeContent method.
+[ManualDealloc, ChildImpl=virtual, ParentImpl=virtual]
+protocol PWebBrowserPersistSerialize {
+  manager PWebBrowserPersistDocument;
+
+parent:
+  // This sends the data with no flow control, so the parent could
+  // wind up buffering an arbitrarily large amount of data...  but
+  // it's a serialized DOM that's already in memory as DOM nodes, so
+  // this is at worst just a constant-factor increase in memory usage.
+  // Also, Chromium does the same thing; see
+  // content::RenderViewImpl::didSerializeDataForFrame.
+  async WriteData(uint8_t[] aData);
+
+  // This is the onFinish method.
+  async __delete__(nsCString aContentType,
+                   nsresult aStatus);
+};
+
+} // namespace mozilla
diff --git a/dom/webbrowserpersist/WebBrowserPersistDocumentChild.cpp b/dom/webbrowserpersist/WebBrowserPersistDocumentChild.cpp
new file mode 100644
index 0000000000..00dbbef08f
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistDocumentChild.cpp
@@ -0,0 +1,157 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 "WebBrowserPersistDocumentChild.h"
+
+#include "mozilla/dom/ContentChild.h"
+#include "mozilla/ipc/IPCStreamUtils.h"
+#include "mozilla/dom/Document.h"
+#include "nsIInputStream.h"
+#include "WebBrowserPersistLocalDocument.h"
+#include "WebBrowserPersistResourcesChild.h"
+#include "WebBrowserPersistSerializeChild.h"
+#include "mozilla/StaticPrefs_fission.h"
+#include "mozilla/net/CookieJarSettings.h"
+
+namespace mozilla {
+
+WebBrowserPersistDocumentChild::WebBrowserPersistDocumentChild() = default;
+
+WebBrowserPersistDocumentChild::~WebBrowserPersistDocumentChild() = default;
+
+void WebBrowserPersistDocumentChild::Start(dom::Document* aDocument) {
+  RefPtr<WebBrowserPersistLocalDocument> doc;
+  if (aDocument) {
+    doc = new WebBrowserPersistLocalDocument(aDocument);
+  }
+  Start(doc);
+}
+
+void WebBrowserPersistDocumentChild::Start(
+    nsIWebBrowserPersistDocument* aDocument) {
+  MOZ_ASSERT(!mDocument);
+  if (!aDocument) {
+    SendInitFailure(NS_ERROR_FAILURE);
+    return;
+  }
+
+  nsCOMPtr<nsIPrincipal> principal;
+  nsCOMPtr<nsIReferrerInfo> referrerInfo;
+  nsCOMPtr<nsICookieJarSettings> cookieJarSettings;
+  WebBrowserPersistDocumentAttrs attrs;
+  nsCOMPtr<nsIInputStream> postDataStream;
+#define ENSURE(e)          \
+  do {                     \
+    nsresult rv = (e);     \
+    if (NS_FAILED(rv)) {   \
+      SendInitFailure(rv); \
+      return;              \
+    }                      \
+  } while (0)
+  ENSURE(aDocument->GetIsPrivate(&(attrs.isPrivate())));
+  ENSURE(aDocument->GetDocumentURI(attrs.documentURI()));
+  ENSURE(aDocument->GetBaseURI(attrs.baseURI()));
+  ENSURE(aDocument->GetContentType(attrs.contentType()));
+  ENSURE(aDocument->GetCharacterSet(attrs.characterSet()));
+  ENSURE(aDocument->GetTitle(attrs.title()));
+  ENSURE(aDocument->GetContentDisposition(attrs.contentDisposition()));
+
+  attrs.sessionHistoryCacheKey() = aDocument->GetCacheKey();
+
+  ENSURE(aDocument->GetPersistFlags(&(attrs.persistFlags())));
+
+  ENSURE(aDocument->GetPrincipal(getter_AddRefs(principal)));
+  ENSURE(ipc::PrincipalToPrincipalInfo(principal, &(attrs.principal())));
+
+  ENSURE(aDocument->GetReferrerInfo(getter_AddRefs(referrerInfo)));
+  attrs.referrerInfo() = referrerInfo;
+
+  ENSURE(aDocument->GetCookieJarSettings(getter_AddRefs(cookieJarSettings)));
+  net::CookieJarSettings::Cast(cookieJarSettings)
+      ->Serialize(attrs.cookieJarSettings());
+
+  ENSURE(aDocument->GetPostData(getter_AddRefs(postDataStream)));
+#undef ENSURE
+
+  Maybe<mozilla::ipc::IPCStream> stream;
+  mozilla::ipc::SerializeIPCStream(postDataStream.forget(), stream,
+                                   /* aAllowLazy */ false);
+
+  mDocument = aDocument;
+  SendAttributes(attrs, stream);
+}
+
+mozilla::ipc::IPCResult WebBrowserPersistDocumentChild::RecvSetPersistFlags(
+    const uint32_t& aNewFlags) {
+  mDocument->SetPersistFlags(aNewFlags);
+  return IPC_OK();
+}
+
+PWebBrowserPersistResourcesChild*
+WebBrowserPersistDocumentChild::AllocPWebBrowserPersistResourcesChild() {
+  auto* actor = new WebBrowserPersistResourcesChild();
+  NS_ADDREF(actor);
+  return actor;
+}
+
+mozilla::ipc::IPCResult
+WebBrowserPersistDocumentChild::RecvPWebBrowserPersistResourcesConstructor(
+    PWebBrowserPersistResourcesChild* aActor) {
+  RefPtr<WebBrowserPersistResourcesChild> visitor =
+      static_cast<WebBrowserPersistResourcesChild*>(aActor);
+  nsresult rv = mDocument->ReadResources(visitor);
+  if (NS_FAILED(rv)) {
+    // This is a sync failure on the child side but an async
+    // failure on the parent side -- it already got NS_OK from
+    // ReadResources, so the error has to be reported via the
+    // visitor instead.
+    visitor->EndVisit(mDocument, rv);
+  }
+  return IPC_OK();
+}
+
+bool WebBrowserPersistDocumentChild::DeallocPWebBrowserPersistResourcesChild(
+    PWebBrowserPersistResourcesChild* aActor) {
+  auto* castActor = static_cast<WebBrowserPersistResourcesChild*>(aActor);
+  NS_RELEASE(castActor);
+  return true;
+}
+
+PWebBrowserPersistSerializeChild*
+WebBrowserPersistDocumentChild::AllocPWebBrowserPersistSerializeChild(
+    const WebBrowserPersistURIMap& aMap,
+    const nsACString& aRequestedContentType, const uint32_t& aEncoderFlags,
+    const uint32_t& aWrapColumn) {
+  auto* actor = new WebBrowserPersistSerializeChild(aMap);
+  NS_ADDREF(actor);
+  return actor;
+}
+
+mozilla::ipc::IPCResult
+WebBrowserPersistDocumentChild::RecvPWebBrowserPersistSerializeConstructor(
+    PWebBrowserPersistSerializeChild* aActor,
+    const WebBrowserPersistURIMap& aMap,
+    const nsACString& aRequestedContentType, const uint32_t& aEncoderFlags,
+    const uint32_t& aWrapColumn) {
+  auto* castActor = static_cast<WebBrowserPersistSerializeChild*>(aActor);
+  // This actor performs the roles of: completion, URI map, and output stream.
+  nsresult rv =
+      mDocument->WriteContent(castActor, castActor, aRequestedContentType,
+                              aEncoderFlags, aWrapColumn, castActor);
+  if (NS_FAILED(rv)) {
+    castActor->OnFinish(mDocument, castActor, aRequestedContentType, rv);
+  }
+  return IPC_OK();
+}
+
+bool WebBrowserPersistDocumentChild::DeallocPWebBrowserPersistSerializeChild(
+    PWebBrowserPersistSerializeChild* aActor) {
+  auto* castActor = static_cast<WebBrowserPersistSerializeChild*>(aActor);
+  NS_RELEASE(castActor);
+  return true;
+}
+
+}  // namespace mozilla
diff --git a/dom/webbrowserpersist/WebBrowserPersistDocumentChild.h b/dom/webbrowserpersist/WebBrowserPersistDocumentChild.h
new file mode 100644
index 0000000000..220811fb6f
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistDocumentChild.h
@@ -0,0 +1,53 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 WebBrowserPersistDocumentChild_h__
+#define WebBrowserPersistDocumentChild_h__
+
+#include "mozilla/PWebBrowserPersistDocumentChild.h"
+#include "nsCOMPtr.h"
+#include "nsIWebBrowserPersistDocument.h"
+
+namespace mozilla {
+
+class WebBrowserPersistDocumentChild final
+    : public PWebBrowserPersistDocumentChild {
+ public:
+  WebBrowserPersistDocumentChild();
+  ~WebBrowserPersistDocumentChild();
+
+  // This sends either Attributes or InitFailure and thereby causes
+  // the actor to leave the START state.
+  void Start(nsIWebBrowserPersistDocument* aDocument);
+  void Start(dom::Document* aDocument);
+
+  mozilla::ipc::IPCResult RecvSetPersistFlags(const uint32_t& aNewFlags);
+
+  PWebBrowserPersistResourcesChild* AllocPWebBrowserPersistResourcesChild();
+  virtual mozilla::ipc::IPCResult RecvPWebBrowserPersistResourcesConstructor(
+      PWebBrowserPersistResourcesChild* aActor) override;
+  bool DeallocPWebBrowserPersistResourcesChild(
+      PWebBrowserPersistResourcesChild* aActor);
+
+  PWebBrowserPersistSerializeChild* AllocPWebBrowserPersistSerializeChild(
+      const WebBrowserPersistURIMap& aMap,
+      const nsACString& aRequestedContentType, const uint32_t& aEncoderFlags,
+      const uint32_t& aWrapColumn);
+  virtual mozilla::ipc::IPCResult RecvPWebBrowserPersistSerializeConstructor(
+      PWebBrowserPersistSerializeChild* aActor,
+      const WebBrowserPersistURIMap& aMap,
+      const nsACString& aRequestedContentType, const uint32_t& aEncoderFlags,
+      const uint32_t& aWrapColumn) override;
+  bool DeallocPWebBrowserPersistSerializeChild(
+      PWebBrowserPersistSerializeChild* aActor);
+
+ private:
+  nsCOMPtr<nsIWebBrowserPersistDocument> mDocument;
+};
+
+}  // namespace mozilla
+
+#endif  // WebBrowserPersistDocumentChild_h__
diff --git a/dom/webbrowserpersist/WebBrowserPersistDocumentParent.cpp b/dom/webbrowserpersist/WebBrowserPersistDocumentParent.cpp
new file mode 100644
index 0000000000..8d08ae5fc5
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistDocumentParent.cpp
@@ -0,0 +1,115 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 "WebBrowserPersistDocumentParent.h"
+
+#include "mozilla/ipc/IPCStreamUtils.h"
+#include "mozilla/dom/PContentParent.h"
+#include "nsIInputStream.h"
+#include "nsThreadUtils.h"
+#include "WebBrowserPersistResourcesParent.h"
+#include "WebBrowserPersistSerializeParent.h"
+#include "WebBrowserPersistRemoteDocument.h"
+
+namespace mozilla {
+
+WebBrowserPersistDocumentParent::WebBrowserPersistDocumentParent()
+    : mReflection(nullptr) {}
+
+void WebBrowserPersistDocumentParent::SetOnReady(
+    nsIWebBrowserPersistDocumentReceiver* aOnReady) {
+  MOZ_ASSERT(aOnReady);
+  MOZ_ASSERT(!mOnReady);
+  MOZ_ASSERT(!mReflection);
+  mOnReady = aOnReady;
+}
+
+void WebBrowserPersistDocumentParent::ActorDestroy(ActorDestroyReason aWhy) {
+  if (mReflection) {
+    mReflection->ActorDestroy();
+    mReflection = nullptr;
+  }
+  if (mOnReady) {
+    // Bug 1202887: If this is part of a subtree destruction, then
+    // anything which could cause another actor in that subtree to
+    // be Send__delete__()ed will cause use-after-free -- such as
+    // dropping the last reference to another document's
+    // WebBrowserPersistRemoteDocument.  To avoid that, defer the
+    // callback until after the entire subtree is destroyed.
+    nsCOMPtr<nsIRunnable> errorLater = NewRunnableMethod<nsresult>(
+        "nsIWebBrowserPersistDocumentReceiver::OnError", mOnReady,
+        &nsIWebBrowserPersistDocumentReceiver::OnError, NS_ERROR_FAILURE);
+    NS_DispatchToCurrentThread(errorLater);
+    mOnReady = nullptr;
+  }
+}
+
+WebBrowserPersistDocumentParent::~WebBrowserPersistDocumentParent() {
+  MOZ_RELEASE_ASSERT(!mReflection);
+  MOZ_ASSERT(!mOnReady);
+}
+
+mozilla::ipc::IPCResult WebBrowserPersistDocumentParent::RecvAttributes(
+    const Attrs& aAttrs, const Maybe<IPCStream>& aPostStream) {
+  // Deserialize the postData unconditionally so that fds aren't leaked.
+  nsCOMPtr<nsIInputStream> postData =
+      mozilla::ipc::DeserializeIPCStream(aPostStream);
+  if (!mOnReady || mReflection) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+  mReflection = new WebBrowserPersistRemoteDocument(this, aAttrs, postData);
+  RefPtr<WebBrowserPersistRemoteDocument> reflection = mReflection;
+  mOnReady->OnDocumentReady(reflection);
+  mOnReady = nullptr;
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult WebBrowserPersistDocumentParent::RecvInitFailure(
+    const nsresult& aFailure) {
+  if (!mOnReady || mReflection) {
+    return IPC_FAIL_NO_REASON(this);
+  }
+  mOnReady->OnError(aFailure);
+  mOnReady = nullptr;
+  // Warning: Send__delete__ deallocates this object.
+  IProtocol* mgr = Manager();
+  if (!Send__delete__(this)) {
+    return IPC_FAIL_NO_REASON(mgr);
+  }
+  return IPC_OK();
+}
+
+PWebBrowserPersistResourcesParent*
+WebBrowserPersistDocumentParent::AllocPWebBrowserPersistResourcesParent() {
+  MOZ_CRASH("Don't use this; construct the actor directly and AddRef.");
+  return nullptr;
+}
+
+bool WebBrowserPersistDocumentParent::DeallocPWebBrowserPersistResourcesParent(
+    PWebBrowserPersistResourcesParent* aActor) {
+  // Turn the ref held by IPC back into an nsRefPtr.
+  RefPtr<WebBrowserPersistResourcesParent> actor =
+      already_AddRefed<WebBrowserPersistResourcesParent>(
+          static_cast<WebBrowserPersistResourcesParent*>(aActor));
+  return true;
+}
+
+PWebBrowserPersistSerializeParent*
+WebBrowserPersistDocumentParent::AllocPWebBrowserPersistSerializeParent(
+    const WebBrowserPersistURIMap& aMap,
+    const nsACString& aRequestedContentType, const uint32_t& aEncoderFlags,
+    const uint32_t& aWrapColumn) {
+  MOZ_CRASH("Don't use this; construct the actor directly.");
+  return nullptr;
+}
+
+bool WebBrowserPersistDocumentParent::DeallocPWebBrowserPersistSerializeParent(
+    PWebBrowserPersistSerializeParent* aActor) {
+  delete aActor;
+  return true;
+}
+
+}  // namespace mozilla
diff --git a/dom/webbrowserpersist/WebBrowserPersistDocumentParent.h b/dom/webbrowserpersist/WebBrowserPersistDocumentParent.h
new file mode 100644
index 0000000000..5f656abbbb
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistDocumentParent.h
@@ -0,0 +1,72 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 WebBrowserPersistDocumentParent_h__
+#define WebBrowserPersistDocumentParent_h__
+
+#include "mozilla/Maybe.h"
+#include "mozilla/PWebBrowserPersistDocumentParent.h"
+#include "nsCOMPtr.h"
+#include "nsIWebBrowserPersistDocument.h"
+
+// This class is the IPC half of the glue between the
+// nsIWebBrowserPersistDocument interface and a remote document.  When
+// (and if) it receives the Attributes message it constructs an
+// WebBrowserPersistRemoteDocument and releases it into the XPCOM
+// universe; otherwise, it invokes the document receiver's error
+// callback.
+//
+// This object's lifetime is the normal IPC lifetime; on destruction,
+// it calls its XPCOM reflection (if it exists yet) to remove that
+// reference.  Normal deletion occurs when the XPCOM object is being
+// destroyed or after an InitFailure is received and handled.
+//
+// See also: BrowserParent::StartPersistence.
+
+namespace mozilla {
+
+class WebBrowserPersistRemoteDocument;
+
+class WebBrowserPersistDocumentParent final
+    : public PWebBrowserPersistDocumentParent {
+ public:
+  WebBrowserPersistDocumentParent();
+  virtual ~WebBrowserPersistDocumentParent();
+
+  // Set a callback to be invoked when the actor leaves the START
+  // state.  This method must be called exactly once while the actor
+  // is still in the START state (or is unconstructed).
+  void SetOnReady(nsIWebBrowserPersistDocumentReceiver* aOnReady);
+
+  using Attrs = WebBrowserPersistDocumentAttrs;
+
+  // IPDL methods:
+  mozilla::ipc::IPCResult RecvAttributes(const Attrs& aAttrs,
+                                         const Maybe<IPCStream>& aPostStream);
+  mozilla::ipc::IPCResult RecvInitFailure(const nsresult& aFailure);
+
+  PWebBrowserPersistResourcesParent* AllocPWebBrowserPersistResourcesParent();
+  bool DeallocPWebBrowserPersistResourcesParent(
+      PWebBrowserPersistResourcesParent* aActor);
+
+  PWebBrowserPersistSerializeParent* AllocPWebBrowserPersistSerializeParent(
+      const WebBrowserPersistURIMap& aMap,
+      const nsACString& aRequestedContentType, const uint32_t& aEncoderFlags,
+      const uint32_t& aWrapColumn);
+  bool DeallocPWebBrowserPersistSerializeParent(
+      PWebBrowserPersistSerializeParent* aActor);
+
+  virtual void ActorDestroy(ActorDestroyReason aWhy) override;
+
+ private:
+  // This is reset to nullptr when the callback is invoked.
+  nsCOMPtr<nsIWebBrowserPersistDocumentReceiver> mOnReady;
+  WebBrowserPersistRemoteDocument* mReflection;
+};
+
+}  // namespace mozilla
+
+#endif  // WebBrowserPersistDocumentParent_h__
diff --git a/dom/webbrowserpersist/WebBrowserPersistLocalDocument.cpp b/dom/webbrowserpersist/WebBrowserPersistLocalDocument.cpp
new file mode 100644
index 0000000000..524f496d35
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistLocalDocument.cpp
@@ -0,0 +1,1319 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * 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 "WebBrowserPersistLocalDocument.h"
+#include "WebBrowserPersistDocumentParent.h"
+
+#include "mozilla/dom/Attr.h"
+#include "mozilla/dom/BrowsingContext.h"
+#include "mozilla/dom/Comment.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/HTMLAnchorElement.h"
+#include "mozilla/dom/HTMLAreaElement.h"
+#include "mozilla/dom/HTMLImageElement.h"
+#include "mozilla/dom/HTMLInputElement.h"
+#include "mozilla/dom/HTMLLinkElement.h"
+#include "mozilla/dom/HTMLObjectElement.h"
+#include "mozilla/dom/HTMLOptionElement.h"
+#include "mozilla/dom/HTMLSharedElement.h"
+#include "mozilla/dom/HTMLTextAreaElement.h"
+#include "mozilla/dom/NodeFilterBinding.h"
+#include "mozilla/dom/ProcessingInstruction.h"
+#include "mozilla/dom/ResponsiveImageSelector.h"
+#include "mozilla/dom/BrowserParent.h"
+#include "mozilla/dom/TreeWalker.h"
+#include "mozilla/Encoding.h"
+#include "mozilla/Unused.h"
+#include "nsComponentManagerUtils.h"
+#include "nsContentUtils.h"
+#include "nsContentCID.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsDOMAttributeMap.h"
+#include "nsFrameLoader.h"
+#include "nsGlobalWindowOuter.h"
+#include "nsIContent.h"
+#include "nsICookieJarSettings.h"
+#include "nsIDOMWindowUtils.h"
+#include "mozilla/dom/Document.h"
+#include "nsIDocumentEncoder.h"
+#include "nsILoadContext.h"
+#include "nsIProtocolHandler.h"
+#include "nsISHEntry.h"
+#include "nsIURIMutator.h"
+#include "nsIWebBrowserPersist.h"
+#include "nsIWebNavigation.h"
+#include "nsIWebPageDescriptor.h"
+#include "nsNetUtil.h"
+#include "nsQueryObject.h"
+
+namespace mozilla {
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(WebBrowserPersistLocalDocument)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(WebBrowserPersistLocalDocument)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(WebBrowserPersistLocalDocument)
+  NS_INTERFACE_MAP_ENTRY(nsIWebBrowserPersistDocument)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION(WebBrowserPersistLocalDocument, mDocument)
+
+WebBrowserPersistLocalDocument::WebBrowserPersistLocalDocument(
+    dom::Document* aDocument)
+    : mDocument(aDocument), mPersistFlags(0) {
+  MOZ_ASSERT(mDocument);
+}
+
+WebBrowserPersistLocalDocument::~WebBrowserPersistLocalDocument() = default;
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::SetPersistFlags(uint32_t aFlags) {
+  mPersistFlags = aFlags;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::GetPersistFlags(uint32_t* aFlags) {
+  *aFlags = mPersistFlags;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::GetIsClosed(bool* aIsClosed) {
+  *aIsClosed = false;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::GetIsPrivate(bool* aIsPrivate) {
+  nsCOMPtr<nsILoadContext> privacyContext = mDocument->GetLoadContext();
+  *aIsPrivate = privacyContext && privacyContext->UsePrivateBrowsing();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::GetDocumentURI(nsACString& aURISpec) {
+  nsCOMPtr<nsIURI> uri = mDocument->GetDocumentURI();
+  if (!uri) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  return uri->GetSpec(aURISpec);
+}
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::GetBaseURI(nsACString& aURISpec) {
+  nsCOMPtr<nsIURI> uri = GetBaseURI();
+  if (!uri) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  return uri->GetSpec(aURISpec);
+}
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::GetContentType(nsACString& aContentType) {
+  nsAutoString utf16Type;
+  mDocument->GetContentType(utf16Type);
+  CopyUTF16toUTF8(utf16Type, aContentType);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::GetCharacterSet(nsACString& aCharSet) {
+  GetCharacterSet()->Name(aCharSet);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::GetTitle(nsAString& aTitle) {
+  nsAutoString titleBuffer;
+  mDocument->GetTitle(titleBuffer);
+  aTitle = titleBuffer;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::GetReferrerInfo(
+    nsIReferrerInfo** aReferrerInfo) {
+  *aReferrerInfo = mDocument->GetReferrerInfo();
+  NS_IF_ADDREF(*aReferrerInfo);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::GetCookieJarSettings(
+    nsICookieJarSettings** aCookieJarSettings) {
+  *aCookieJarSettings = mDocument->CookieJarSettings();
+  NS_ADDREF(*aCookieJarSettings);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::GetContentDisposition(nsAString& aCD) {
+  nsCOMPtr<nsPIDOMWindowOuter> window = mDocument->GetWindow();
+  if (NS_WARN_IF(!window)) {
+    aCD.SetIsVoid(true);
+    return NS_OK;
+  }
+  nsCOMPtr<nsIDOMWindowUtils> utils =
+      nsGlobalWindowOuter::Cast(window)->WindowUtils();
+  nsresult rv = utils->GetDocumentMetadata(u"content-disposition"_ns, aCD);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    aCD.SetIsVoid(true);
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::GetCacheKey(uint32_t* aKey) {
+  Maybe<uint32_t> cacheKey;
+
+  if (nsDocShell* docShell = nsDocShell::Cast(mDocument->GetDocShell())) {
+    cacheKey = docShell->GetCacheKeyFromCurrentEntry();
+  }
+  *aKey = cacheKey.valueOr(0);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::GetPostData(nsIInputStream** aStream) {
+  nsCOMPtr<nsIInputStream> postData;
+  if (nsDocShell* docShell = nsDocShell::Cast(mDocument->GetDocShell())) {
+    postData = docShell->GetPostDataFromCurrentEntry();
+  }
+
+  postData.forget(aStream);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::GetPrincipal(nsIPrincipal** aPrincipal) {
+  nsCOMPtr<nsIPrincipal> nodePrincipal = mDocument->NodePrincipal();
+  nodePrincipal.forget(aPrincipal);
+  return NS_OK;
+}
+
+already_AddRefed<nsISHEntry> WebBrowserPersistLocalDocument::GetHistory() {
+  nsCOMPtr<nsPIDOMWindowOuter> window = mDocument->GetWindow();
+  if (NS_WARN_IF(!window)) {
+    return nullptr;
+  }
+  nsCOMPtr<nsIWebNavigation> webNav = do_GetInterface(window);
+  if (NS_WARN_IF(!webNav)) {
+    return nullptr;
+  }
+  nsCOMPtr<nsIWebPageDescriptor> desc = do_QueryInterface(webNav);
+  if (NS_WARN_IF(!desc)) {
+    return nullptr;
+  }
+  nsCOMPtr<nsISupports> curDesc;
+  nsresult rv = desc->GetCurrentDescriptor(getter_AddRefs(curDesc));
+  // This can fail if, e.g., the document is a Print Preview.
+  if (NS_FAILED(rv) || NS_WARN_IF(!curDesc)) {
+    return nullptr;
+  }
+  nsCOMPtr<nsISHEntry> history = do_QueryInterface(curDesc);
+  return history.forget();
+}
+
+NotNull<const Encoding*> WebBrowserPersistLocalDocument::GetCharacterSet()
+    const {
+  return mDocument->GetDocumentCharacterSet();
+}
+
+uint32_t WebBrowserPersistLocalDocument::GetPersistFlags() const {
+  return mPersistFlags;
+}
+
+nsIURI* WebBrowserPersistLocalDocument::GetBaseURI() const {
+  return mDocument->GetBaseURI();
+}
+
+namespace {
+
+// Helper class for ReadResources().
+class ResourceReader final : public nsIWebBrowserPersistDocumentReceiver {
+ public:
+  ResourceReader(WebBrowserPersistLocalDocument* aParent,
+                 nsIWebBrowserPersistResourceVisitor* aVisitor);
+  nsresult OnWalkDOMNode(nsINode* aNode);
+
+  // This is called both to indicate the end of the document walk
+  // and when a subdocument is (maybe asynchronously) sent to the
+  // visitor.  The call to EndVisit needs to happen after both of
+  // those have finished.
+  void DocumentDone(nsresult aStatus);
+
+  NS_DECL_NSIWEBBROWSERPERSISTDOCUMENTRECEIVER
+  NS_DECL_ISUPPORTS
+
+ private:
+  RefPtr<WebBrowserPersistLocalDocument> mParent;
+  nsCOMPtr<nsIWebBrowserPersistResourceVisitor> mVisitor;
+  nsCOMPtr<nsIURI> mCurrentBaseURI;
+  uint32_t mPersistFlags;
+
+  // The number of DocumentDone calls after which EndVisit will be
+  // called on the visitor.  Counts the main document if it's still
+  // being walked and any outstanding asynchronous subdocument
+  // StartPersistence calls.
+  size_t mOutstandingDocuments;
+  // Collects the status parameters to DocumentDone calls.
+  nsresult mEndStatus;
+
+  nsresult OnWalkURI(const nsACString& aURISpec,
+                     nsContentPolicyType aContentPolicyType);
+  nsresult OnWalkURI(nsIURI* aURI, nsContentPolicyType aContentPolicyType);
+  nsresult OnWalkAttribute(dom::Element* aElement,
+                           nsContentPolicyType aContentPolicyType,
+                           const char* aAttribute,
+                           const char* aNamespaceURI = "");
+  nsresult OnWalkSubframe(nsINode* aNode);
+  nsresult OnWalkSrcSet(dom::Element* aElement);
+
+  ~ResourceReader();
+
+  using IWBP = nsIWebBrowserPersist;
+};
+
+NS_IMPL_ISUPPORTS(ResourceReader, nsIWebBrowserPersistDocumentReceiver)
+
+ResourceReader::ResourceReader(WebBrowserPersistLocalDocument* aParent,
+                               nsIWebBrowserPersistResourceVisitor* aVisitor)
+    : mParent(aParent),
+      mVisitor(aVisitor),
+      mCurrentBaseURI(aParent->GetBaseURI()),
+      mPersistFlags(aParent->GetPersistFlags()),
+      mOutstandingDocuments(1),
+      mEndStatus(NS_OK) {
+  MOZ_ASSERT(mCurrentBaseURI);
+}
+
+ResourceReader::~ResourceReader() { MOZ_ASSERT(mOutstandingDocuments == 0); }
+
+void ResourceReader::DocumentDone(nsresult aStatus) {
+  MOZ_ASSERT(mOutstandingDocuments > 0);
+  if (NS_SUCCEEDED(mEndStatus)) {
+    mEndStatus = aStatus;
+  }
+  if (--mOutstandingDocuments == 0) {
+    mVisitor->EndVisit(mParent, mEndStatus);
+  }
+}
+
+nsresult ResourceReader::OnWalkSubframe(nsINode* aNode) {
+  RefPtr<nsFrameLoaderOwner> loaderOwner = do_QueryObject(aNode);
+  NS_ENSURE_STATE(loaderOwner);
+  RefPtr<nsFrameLoader> loader = loaderOwner->GetFrameLoader();
+  NS_ENSURE_STATE(loader);
+
+  RefPtr<dom::BrowsingContext> context = loader->GetBrowsingContext();
+  NS_ENSURE_STATE(context);
+
+  if (loader->IsRemoteFrame()) {
+    mVisitor->VisitBrowsingContext(mParent, context);
+    return NS_OK;
+  }
+
+  ++mOutstandingDocuments;
+  ErrorResult err;
+  loader->StartPersistence(context, this, err);
+  nsresult rv = err.StealNSResult();
+  if (NS_FAILED(rv)) {
+    if (rv == NS_ERROR_NO_CONTENT) {
+      // Just ignore frames with no content document.
+      rv = NS_OK;
+    }
+    // StartPersistence won't eventually call this if it failed,
+    // so this does so (to keep mOutstandingDocuments correct).
+    DocumentDone(rv);
+  }
+  return rv;
+}
+
+NS_IMETHODIMP
+ResourceReader::OnDocumentReady(nsIWebBrowserPersistDocument* aDocument) {
+  mVisitor->VisitDocument(mParent, aDocument);
+  DocumentDone(NS_OK);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+ResourceReader::OnError(nsresult aFailure) {
+  DocumentDone(aFailure);
+  return NS_OK;
+}
+
+nsresult ResourceReader::OnWalkURI(nsIURI* aURI,
+                                   nsContentPolicyType aContentPolicyType) {
+  // Test if this URI should be persisted. By default
+  // we should assume the URI  is persistable.
+  bool doNotPersistURI;
+  nsresult rv = NS_URIChainHasFlags(
+      aURI, nsIProtocolHandler::URI_NON_PERSISTABLE, &doNotPersistURI);
+  if (NS_SUCCEEDED(rv) && doNotPersistURI) {
+    return NS_OK;
+  }
+
+  nsAutoCString stringURI;
+  rv = aURI->GetSpec(stringURI);
+  NS_ENSURE_SUCCESS(rv, rv);
+  return mVisitor->VisitResource(mParent, stringURI, aContentPolicyType);
+}
+
+nsresult ResourceReader::OnWalkURI(const nsACString& aURISpec,
+                                   nsContentPolicyType aContentPolicyType) {
+  nsresult rv;
+  nsCOMPtr<nsIURI> uri;
+
+  rv = NS_NewURI(getter_AddRefs(uri), aURISpec, mParent->GetCharacterSet(),
+                 mCurrentBaseURI);
+  if (NS_FAILED(rv)) {
+    // We don't want to break saving a page in case of a malformed URI.
+    return NS_OK;
+  }
+  return OnWalkURI(uri, aContentPolicyType);
+}
+
+static void ExtractAttribute(dom::Element* aElement, const char* aAttribute,
+                             const char* aNamespaceURI, nsCString& aValue) {
+  // Find the named URI attribute on the (element) node and store
+  // a reference to the URI that maps onto a local file name
+
+  RefPtr<nsDOMAttributeMap> attrMap = aElement->Attributes();
+
+  NS_ConvertASCIItoUTF16 namespaceURI(aNamespaceURI);
+  NS_ConvertASCIItoUTF16 attribute(aAttribute);
+  RefPtr<dom::Attr> attr = attrMap->GetNamedItemNS(namespaceURI, attribute);
+  if (attr) {
+    nsAutoString value;
+    attr->GetValue(value);
+    CopyUTF16toUTF8(value, aValue);
+  } else {
+    aValue.Truncate();
+  }
+}
+
+nsresult ResourceReader::OnWalkAttribute(dom::Element* aElement,
+                                         nsContentPolicyType aContentPolicyType,
+                                         const char* aAttribute,
+                                         const char* aNamespaceURI) {
+  nsAutoCString uriSpec;
+  ExtractAttribute(aElement, aAttribute, aNamespaceURI, uriSpec);
+  if (uriSpec.IsEmpty()) {
+    return NS_OK;
+  }
+  return OnWalkURI(uriSpec, aContentPolicyType);
+}
+
+nsresult ResourceReader::OnWalkSrcSet(dom::Element* aElement) {
+  nsAutoString srcSet;
+  if (!aElement->GetAttr(nsGkAtoms::srcset, srcSet)) {
+    return NS_OK;
+  }
+
+  nsresult rv = NS_OK;
+  auto eachCandidate = [&](dom::ResponsiveImageCandidate&& aCandidate) {
+    if (!aCandidate.IsValid() || NS_FAILED(rv)) {
+      return;
+    }
+    rv = OnWalkURI(NS_ConvertUTF16toUTF8(aCandidate.URLString()),
+                   nsIContentPolicy::TYPE_IMAGE);
+  };
+  dom::ResponsiveImageSelector::ParseSourceSet(srcSet, eachCandidate);
+  return rv;
+}
+
+static nsresult GetXMLStyleSheetLink(dom::ProcessingInstruction* aPI,
+                                     nsAString& aHref) {
+  nsAutoString data;
+  aPI->GetData(data);
+
+  nsContentUtils::GetPseudoAttributeValue(data, nsGkAtoms::href, aHref);
+  return NS_OK;
+}
+
+nsresult ResourceReader::OnWalkDOMNode(nsINode* aNode) {
+  // Fixup xml-stylesheet processing instructions
+  if (auto nodeAsPI = dom::ProcessingInstruction::FromNode(aNode)) {
+    nsAutoString target;
+    nodeAsPI->GetTarget(target);
+    if (target.EqualsLiteral("xml-stylesheet")) {
+      nsAutoString href;
+      GetXMLStyleSheetLink(nodeAsPI, href);
+      if (!href.IsEmpty()) {
+        return OnWalkURI(NS_ConvertUTF16toUTF8(href),
+                         nsIContentPolicy::TYPE_STYLESHEET);
+      }
+    }
+    return NS_OK;
+  }
+
+  // Test the node to see if it's an image, frame, iframe, css, js
+  if (auto* img = dom::HTMLImageElement::FromNode(*aNode)) {
+    MOZ_TRY(OnWalkAttribute(img, nsIContentPolicy::TYPE_IMAGE, "src"));
+    MOZ_TRY(OnWalkSrcSet(img));
+    return NS_OK;
+  }
+
+  if (aNode->IsSVGElement(nsGkAtoms::image)) {
+    MOZ_TRY(OnWalkAttribute(aNode->AsElement(), nsIContentPolicy::TYPE_IMAGE,
+                            "href"));
+    return OnWalkAttribute(aNode->AsElement(), nsIContentPolicy::TYPE_IMAGE,
+                           "href", "http://www.w3.org/1999/xlink");
+  }
+
+  if (aNode->IsAnyOfHTMLElements(nsGkAtoms::audio, nsGkAtoms::video)) {
+    return OnWalkAttribute(aNode->AsElement(), nsIContentPolicy::TYPE_MEDIA,
+                           "src");
+  }
+
+  if (aNode->IsHTMLElement(nsGkAtoms::source)) {
+    MOZ_TRY(OnWalkSrcSet(aNode->AsElement()));
+    return OnWalkAttribute(aNode->AsElement(), nsIContentPolicy::TYPE_MEDIA,
+                           "src");
+  }
+
+  if (aNode->IsHTMLElement(nsGkAtoms::body)) {
+    return OnWalkAttribute(aNode->AsElement(), nsIContentPolicy::TYPE_IMAGE,
+                           "background");
+  }
+
+  if (aNode->IsHTMLElement(nsGkAtoms::table)) {
+    return OnWalkAttribute(aNode->AsElement(), nsIContentPolicy::TYPE_IMAGE,
+                           "background");
+  }
+
+  if (aNode->IsHTMLElement(nsGkAtoms::tr)) {
+    return OnWalkAttribute(aNode->AsElement(), nsIContentPolicy::TYPE_IMAGE,
+                           "background");
+  }
+
+  if (aNode->IsAnyOfHTMLElements(nsGkAtoms::td, nsGkAtoms::th)) {
+    return OnWalkAttribute(aNode->AsElement(), nsIContentPolicy::TYPE_IMAGE,
+                           "background");
+  }
+
+  if (aNode->IsHTMLElement(nsGkAtoms::script)) {
+    return OnWalkAttribute(aNode->AsElement(), nsIContentPolicy::TYPE_SCRIPT,
+                           "src");
+  }
+
+  if (aNode->IsSVGElement(nsGkAtoms::script)) {
+    MOZ_TRY(OnWalkAttribute(aNode->AsElement(), nsIContentPolicy::TYPE_SCRIPT,
+                            "href"));
+    return OnWalkAttribute(aNode->AsElement(), nsIContentPolicy::TYPE_SCRIPT,
+                           "href", "http://www.w3.org/1999/xlink");
+  }
+
+  if (aNode->IsHTMLElement(nsGkAtoms::embed)) {
+    return OnWalkAttribute(aNode->AsElement(), nsIContentPolicy::TYPE_OBJECT,
+                           "src");
+  }
+
+  if (aNode->IsHTMLElement(nsGkAtoms::object)) {
+    return OnWalkAttribute(aNode->AsElement(), nsIContentPolicy::TYPE_OBJECT,
+                           "data");
+  }
+
+  if (auto nodeAsLink = dom::HTMLLinkElement::FromNode(aNode)) {
+    // Test if the link has a rel value indicating it to be a stylesheet
+    nsAutoString linkRel;
+    nodeAsLink->GetRel(linkRel);
+    if (!linkRel.IsEmpty()) {
+      nsReadingIterator<char16_t> start;
+      nsReadingIterator<char16_t> end;
+      nsReadingIterator<char16_t> current;
+
+      linkRel.BeginReading(start);
+      linkRel.EndReading(end);
+
+      // Walk through space delimited string looking for "stylesheet"
+      for (current = start; current != end; ++current) {
+        // Ignore whitespace
+        if (nsCRT::IsAsciiSpace(*current)) {
+          continue;
+        }
+
+        // Grab the next space delimited word
+        nsReadingIterator<char16_t> startWord = current;
+        do {
+          ++current;
+        } while (current != end && !nsCRT::IsAsciiSpace(*current));
+
+        // Store the link for fix up if it says "stylesheet"
+        if (Substring(startWord, current)
+                .LowerCaseEqualsLiteral("stylesheet")) {
+          OnWalkAttribute(aNode->AsElement(), nsIContentPolicy::TYPE_STYLESHEET,
+                          "href");
+          return NS_OK;
+        }
+        if (current == end) {
+          break;
+        }
+      }
+    }
+    return NS_OK;
+  }
+
+  if (aNode->IsHTMLElement(nsGkAtoms::frame)) {
+    return OnWalkSubframe(aNode);
+  }
+
+  if (aNode->IsHTMLElement(nsGkAtoms::iframe) &&
+      !(mPersistFlags & IWBP::PERSIST_FLAGS_IGNORE_IFRAMES)) {
+    return OnWalkSubframe(aNode);
+  }
+
+  auto nodeAsInput = dom::HTMLInputElement::FromNode(aNode);
+  if (nodeAsInput) {
+    return OnWalkAttribute(aNode->AsElement(), nsIContentPolicy::TYPE_IMAGE,
+                           "src");
+  }
+
+  return NS_OK;
+}
+
+// Helper class for node rewriting in writeContent().
+class PersistNodeFixup final : public nsIDocumentEncoderNodeFixup {
+ public:
+  PersistNodeFixup(WebBrowserPersistLocalDocument* aParent,
+                   nsIWebBrowserPersistURIMap* aMap, nsIURI* aTargetURI);
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIDOCUMENTENCODERNODEFIXUP
+ private:
+  virtual ~PersistNodeFixup() = default;
+  RefPtr<WebBrowserPersistLocalDocument> mParent;
+  nsClassHashtable<nsCStringHashKey, nsCString> mMap;
+  nsCOMPtr<nsIURI> mCurrentBaseURI;
+  nsCOMPtr<nsIURI> mTargetBaseURI;
+
+  bool IsFlagSet(uint32_t aFlag) const {
+    return mParent->GetPersistFlags() & aFlag;
+  }
+
+  nsresult GetNodeToFixup(nsINode* aNodeIn, nsINode** aNodeOut);
+  nsresult FixupURI(nsAString& aURI);
+  nsresult FixupAttribute(nsINode* aNode, const char* aAttribute,
+                          const char* aNamespaceURI = "");
+  nsresult FixupAnchor(nsINode* aNode);
+  nsresult FixupXMLStyleSheetLink(dom::ProcessingInstruction* aPI,
+                                  const nsAString& aHref);
+
+  nsresult FixupSrcSet(nsINode*);
+
+  using IWBP = nsIWebBrowserPersist;
+};
+
+NS_IMPL_ISUPPORTS(PersistNodeFixup, nsIDocumentEncoderNodeFixup)
+
+PersistNodeFixup::PersistNodeFixup(WebBrowserPersistLocalDocument* aParent,
+                                   nsIWebBrowserPersistURIMap* aMap,
+                                   nsIURI* aTargetURI)
+    : mParent(aParent),
+      mCurrentBaseURI(aParent->GetBaseURI()),
+      mTargetBaseURI(aTargetURI) {
+  if (aMap) {
+    uint32_t mapSize;
+    nsresult rv = aMap->GetNumMappedURIs(&mapSize);
+    MOZ_ASSERT(NS_SUCCEEDED(rv));
+    NS_ENSURE_SUCCESS_VOID(rv);
+    for (uint32_t i = 0; i < mapSize; ++i) {
+      nsAutoCString urlFrom;
+      auto urlTo = MakeUnique<nsCString>();
+
+      rv = aMap->GetURIMapping(i, urlFrom, *urlTo);
+      MOZ_ASSERT(NS_SUCCEEDED(rv));
+      if (NS_SUCCEEDED(rv)) {
+        mMap.InsertOrUpdate(urlFrom, std::move(urlTo));
+      }
+    }
+  }
+}
+
+nsresult PersistNodeFixup::GetNodeToFixup(nsINode* aNodeIn,
+                                          nsINode** aNodeOut) {
+  // Avoid mixups in FixupNode that could leak objects; this goes
+  // against the usual out parameter convention, but it's a private
+  // method so shouldn't be a problem.
+  MOZ_ASSERT(!*aNodeOut);
+
+  if (!IsFlagSet(IWBP::PERSIST_FLAGS_FIXUP_ORIGINAL_DOM)) {
+    ErrorResult rv;
+    *aNodeOut = aNodeIn->CloneNode(false, rv).take();
+    return rv.StealNSResult();
+  }
+
+  NS_ADDREF(*aNodeOut = aNodeIn);
+  return NS_OK;
+}
+
+nsresult PersistNodeFixup::FixupURI(nsAString& aURI) {
+  // get the current location of the file (absolutized)
+  nsCOMPtr<nsIURI> uri;
+  nsresult rv = NS_NewURI(getter_AddRefs(uri), aURI, mParent->GetCharacterSet(),
+                          mCurrentBaseURI);
+  NS_ENSURE_SUCCESS(rv, rv);
+  nsAutoCString spec;
+  rv = uri->GetSpec(spec);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  const nsCString* replacement = mMap.Get(spec);
+  if (!replacement) {
+    // Note that most callers ignore this "failure".
+    return NS_ERROR_FAILURE;
+  }
+  if (!replacement->IsEmpty()) {
+    CopyUTF8toUTF16(*replacement, aURI);
+  }
+  return NS_OK;
+}
+
+nsresult PersistNodeFixup::FixupSrcSet(nsINode* aNode) {
+  dom::Element* element = aNode->AsElement();
+  nsAutoString originalSrcSet;
+  if (!element->GetAttr(nsGkAtoms::srcset, originalSrcSet)) {
+    return NS_OK;
+  }
+  nsAutoString newSrcSet;
+  bool first = true;
+  auto eachCandidate = [&](dom::ResponsiveImageCandidate&& aCandidate) {
+    if (!aCandidate.IsValid()) {
+      return;
+    }
+    if (!first) {
+      newSrcSet.AppendLiteral(", ");
+    }
+    first = false;
+    nsAutoString uri(aCandidate.URLString());
+    FixupURI(uri);
+    newSrcSet.Append(uri);
+    aCandidate.AppendDescriptors(newSrcSet);
+  };
+  dom::ResponsiveImageSelector::ParseSourceSet(originalSrcSet, eachCandidate);
+  element->SetAttr(nsGkAtoms::srcset, newSrcSet, IgnoreErrors());
+  return NS_OK;
+}
+
+nsresult PersistNodeFixup::FixupAttribute(nsINode* aNode,
+                                          const char* aAttribute,
+                                          const char* aNamespaceURI) {
+  MOZ_ASSERT(aNode->IsElement());
+  dom::Element* element = aNode->AsElement();
+
+  RefPtr<nsDOMAttributeMap> attrMap = element->Attributes();
+
+  NS_ConvertASCIItoUTF16 attribute(aAttribute);
+  NS_ConvertASCIItoUTF16 namespaceURI(aNamespaceURI);
+  RefPtr<dom::Attr> attr = attrMap->GetNamedItemNS(namespaceURI, attribute);
+  nsresult rv = NS_OK;
+  if (attr) {
+    nsString uri;
+    attr->GetValue(uri);
+    rv = FixupURI(uri);
+    if (NS_SUCCEEDED(rv)) {
+      attr->SetValue(uri, IgnoreErrors());
+    }
+  }
+
+  return rv;
+}
+
+nsresult PersistNodeFixup::FixupAnchor(nsINode* aNode) {
+  if (IsFlagSet(IWBP::PERSIST_FLAGS_DONT_FIXUP_LINKS)) {
+    return NS_OK;
+  }
+
+  MOZ_ASSERT(aNode->IsElement());
+  dom::Element* element = aNode->AsElement();
+
+  RefPtr<nsDOMAttributeMap> attrMap = element->Attributes();
+
+  // Make all anchor links absolute so they point off onto the Internet
+  nsString attribute(u"href"_ns);
+  RefPtr<dom::Attr> attr = attrMap->GetNamedItem(attribute);
+  if (attr) {
+    nsString oldValue;
+    attr->GetValue(oldValue);
+    NS_ConvertUTF16toUTF8 oldCValue(oldValue);
+
+    // Skip empty values and self-referencing bookmarks
+    if (oldCValue.IsEmpty() || oldCValue.CharAt(0) == '#') {
+      return NS_OK;
+    }
+
+    // if saving file to same location, we don't need to do any fixup
+    bool isEqual;
+    if (mTargetBaseURI &&
+        NS_SUCCEEDED(mCurrentBaseURI->Equals(mTargetBaseURI, &isEqual)) &&
+        isEqual) {
+      return NS_OK;
+    }
+
+    nsCOMPtr<nsIURI> relativeURI;
+    relativeURI = IsFlagSet(IWBP::PERSIST_FLAGS_FIXUP_LINKS_TO_DESTINATION)
+                      ? mTargetBaseURI
+                      : mCurrentBaseURI;
+    // Make a new URI to replace the current one
+    nsCOMPtr<nsIURI> newURI;
+    nsresult rv = NS_NewURI(getter_AddRefs(newURI), oldCValue,
+                            mParent->GetCharacterSet(), relativeURI);
+    if (NS_SUCCEEDED(rv) && newURI) {
+      Unused << NS_MutateURI(newURI).SetUserPass(""_ns).Finalize(newURI);
+      nsAutoCString uriSpec;
+      rv = newURI->GetSpec(uriSpec);
+      NS_ENSURE_SUCCESS(rv, rv);
+      attr->SetValue(NS_ConvertUTF8toUTF16(uriSpec), IgnoreErrors());
+    }
+  }
+
+  return NS_OK;
+}
+
+static void AppendXMLAttr(const nsAString& key, const nsAString& aValue,
+                          nsAString& aBuffer) {
+  if (!aBuffer.IsEmpty()) {
+    aBuffer.Append(' ');
+  }
+  aBuffer.Append(key);
+  aBuffer.AppendLiteral(R"(=")");
+  for (size_t i = 0; i < aValue.Length(); ++i) {
+    switch (aValue[i]) {
+      case '&':
+        aBuffer.AppendLiteral("&amp;");
+        break;
+      case '<':
+        aBuffer.AppendLiteral("&lt;");
+        break;
+      case '>':
+        aBuffer.AppendLiteral("&gt;");
+        break;
+      case '"':
+        aBuffer.AppendLiteral("&quot;");
+        break;
+      default:
+        aBuffer.Append(aValue[i]);
+        break;
+    }
+  }
+  aBuffer.Append('"');
+}
+
+nsresult PersistNodeFixup::FixupXMLStyleSheetLink(
+    dom::ProcessingInstruction* aPI, const nsAString& aHref) {
+  NS_ENSURE_ARG_POINTER(aPI);
+
+  nsAutoString data;
+  aPI->GetData(data);
+
+  nsAutoString href;
+  nsContentUtils::GetPseudoAttributeValue(data, nsGkAtoms::href, href);
+
+  // Construct and set a new data value for the xml-stylesheet
+  if (!aHref.IsEmpty() && !href.IsEmpty()) {
+    nsAutoString alternate;
+    nsAutoString charset;
+    nsAutoString title;
+    nsAutoString type;
+    nsAutoString media;
+
+    nsContentUtils::GetPseudoAttributeValue(data, nsGkAtoms::alternate,
+                                            alternate);
+    nsContentUtils::GetPseudoAttributeValue(data, nsGkAtoms::charset, charset);
+    nsContentUtils::GetPseudoAttributeValue(data, nsGkAtoms::title, title);
+    nsContentUtils::GetPseudoAttributeValue(data, nsGkAtoms::type, type);
+    nsContentUtils::GetPseudoAttributeValue(data, nsGkAtoms::media, media);
+
+    nsAutoString newData;
+    AppendXMLAttr(u"href"_ns, aHref, newData);
+    if (!title.IsEmpty()) {
+      AppendXMLAttr(u"title"_ns, title, newData);
+    }
+    if (!media.IsEmpty()) {
+      AppendXMLAttr(u"media"_ns, media, newData);
+    }
+    if (!type.IsEmpty()) {
+      AppendXMLAttr(u"type"_ns, type, newData);
+    }
+    if (!charset.IsEmpty()) {
+      AppendXMLAttr(u"charset"_ns, charset, newData);
+    }
+    if (!alternate.IsEmpty()) {
+      AppendXMLAttr(u"alternate"_ns, alternate, newData);
+    }
+    aPI->SetData(newData, IgnoreErrors());
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+PersistNodeFixup::FixupNode(nsINode* aNodeIn, bool* aSerializeCloneKids,
+                            nsINode** aNodeOut) {
+  *aNodeOut = nullptr;
+  *aSerializeCloneKids = false;
+
+  uint16_t type = aNodeIn->NodeType();
+  if (type != nsINode::ELEMENT_NODE &&
+      type != nsINode::PROCESSING_INSTRUCTION_NODE) {
+    return NS_OK;
+  }
+
+  MOZ_ASSERT(aNodeIn->IsContent());
+
+  // Fixup xml-stylesheet processing instructions
+  if (auto nodeAsPI = dom::ProcessingInstruction::FromNode(aNodeIn)) {
+    nsAutoString target;
+    nodeAsPI->GetTarget(target);
+    if (target.EqualsLiteral("xml-stylesheet")) {
+      nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+      if (NS_SUCCEEDED(rv) && *aNodeOut) {
+        MOZ_ASSERT((*aNodeOut)->IsProcessingInstruction());
+        auto nodeAsPI = static_cast<dom::ProcessingInstruction*>(*aNodeOut);
+        nsAutoString href;
+        GetXMLStyleSheetLink(nodeAsPI, href);
+        if (!href.IsEmpty()) {
+          FixupURI(href);
+          FixupXMLStyleSheetLink(nodeAsPI, href);
+        }
+      }
+    }
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsIContent> content = do_QueryInterface(aNodeIn);
+  if (!content) {
+    return NS_OK;
+  }
+
+  // BASE elements are replaced by a comment so relative links are not hosed.
+  if (!IsFlagSet(IWBP::PERSIST_FLAGS_NO_BASE_TAG_MODIFICATIONS) &&
+      content->IsHTMLElement(nsGkAtoms::base)) {
+    // Base uses HTMLSharedElement, which would be awkward to implement
+    // FromContent on, since it represents multiple elements. Since we've
+    // already checked IsHTMLElement here, just cast as we were doing.
+    auto* base = static_cast<dom::HTMLSharedElement*>(content.get());
+    dom::Document* ownerDoc = base->OwnerDoc();
+
+    nsAutoString href;
+    base->GetHref(href);  // Doesn't matter if this fails
+    nsAutoString commentText;
+    commentText.AssignLiteral(" base ");
+    if (!href.IsEmpty()) {
+      commentText += u"href=\""_ns + href + u"\" "_ns;
+    }
+    *aNodeOut = ownerDoc->CreateComment(commentText).take();
+    return NS_OK;
+  }
+
+  // Fix up href and file links in the elements
+  RefPtr<dom::HTMLAnchorElement> nodeAsAnchor =
+      dom::HTMLAnchorElement::FromNode(content);
+  if (nodeAsAnchor) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      FixupAnchor(*aNodeOut);
+    }
+    return rv;
+  }
+
+  RefPtr<dom::HTMLAreaElement> nodeAsArea =
+      dom::HTMLAreaElement::FromNode(content);
+  if (nodeAsArea) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      FixupAnchor(*aNodeOut);
+    }
+    return rv;
+  }
+
+  if (content->IsHTMLElement(nsGkAtoms::body)) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      FixupAttribute(*aNodeOut, "background");
+    }
+    return rv;
+  }
+
+  if (content->IsHTMLElement(nsGkAtoms::table)) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      FixupAttribute(*aNodeOut, "background");
+    }
+    return rv;
+  }
+
+  if (content->IsHTMLElement(nsGkAtoms::tr)) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      FixupAttribute(*aNodeOut, "background");
+    }
+    return rv;
+  }
+
+  if (content->IsAnyOfHTMLElements(nsGkAtoms::td, nsGkAtoms::th)) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      FixupAttribute(*aNodeOut, "background");
+    }
+    return rv;
+  }
+
+  if (content->IsHTMLElement(nsGkAtoms::img)) {
+    MOZ_TRY(GetNodeToFixup(aNodeIn, aNodeOut));
+    if (!*aNodeOut) {
+      return NS_OK;
+    }
+
+    // Disable image loads
+    nsCOMPtr<nsIImageLoadingContent> imgCon = do_QueryInterface(*aNodeOut);
+    if (imgCon) {
+      imgCon->SetLoadingEnabled(false);
+    }
+    // FIXME(emilio): Why fixing up <img href>? Looks bogus
+    FixupAnchor(*aNodeOut);
+    FixupAttribute(*aNodeOut, "src");
+    FixupSrcSet(*aNodeOut);
+    return NS_OK;
+  }
+
+  if (content->IsAnyOfHTMLElements(nsGkAtoms::audio, nsGkAtoms::video)) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      FixupAttribute(*aNodeOut, "src");
+    }
+    return rv;
+  }
+
+  if (content->IsHTMLElement(nsGkAtoms::source)) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      FixupAttribute(*aNodeOut, "src");
+      FixupSrcSet(*aNodeOut);
+    }
+    return rv;
+  }
+
+  if (content->IsSVGElement(nsGkAtoms::image)) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      // Disable image loads
+      nsCOMPtr<nsIImageLoadingContent> imgCon = do_QueryInterface(*aNodeOut);
+      if (imgCon) imgCon->SetLoadingEnabled(false);
+
+      // FixupAnchor(*aNodeOut);  // XXXjwatt: is this line needed?
+      FixupAttribute(*aNodeOut, "href");
+      FixupAttribute(*aNodeOut, "href", "http://www.w3.org/1999/xlink");
+    }
+    return rv;
+  }
+
+  if (content->IsHTMLElement(nsGkAtoms::script)) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      FixupAttribute(*aNodeOut, "src");
+    }
+    return rv;
+  }
+
+  if (content->IsSVGElement(nsGkAtoms::script)) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      FixupAttribute(*aNodeOut, "href");
+      FixupAttribute(*aNodeOut, "href", "http://www.w3.org/1999/xlink");
+    }
+    return rv;
+  }
+
+  if (content->IsHTMLElement(nsGkAtoms::embed)) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      FixupAttribute(*aNodeOut, "src");
+    }
+    return rv;
+  }
+
+  if (content->IsHTMLElement(nsGkAtoms::object)) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      FixupAttribute(*aNodeOut, "data");
+    }
+    return rv;
+  }
+
+  if (content->IsHTMLElement(nsGkAtoms::link)) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      // First see if the link represents linked content
+      rv = FixupAttribute(*aNodeOut, "href");
+      if (NS_FAILED(rv)) {
+        // Perhaps this link is actually an anchor to related content
+        FixupAnchor(*aNodeOut);
+      }
+      // TODO if "type" attribute == "text/css"
+      //        fixup stylesheet
+    }
+    return rv;
+  }
+
+  if (content->IsHTMLElement(nsGkAtoms::frame)) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      FixupAttribute(*aNodeOut, "src");
+    }
+    return rv;
+  }
+
+  if (content->IsHTMLElement(nsGkAtoms::iframe)) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      FixupAttribute(*aNodeOut, "src");
+    }
+    return rv;
+  }
+
+  RefPtr<dom::HTMLInputElement> nodeAsInput =
+      dom::HTMLInputElement::FromNodeOrNull(content);
+  if (nodeAsInput) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      // Disable image loads
+      nsCOMPtr<nsIImageLoadingContent> imgCon = do_QueryInterface(*aNodeOut);
+      if (imgCon) {
+        imgCon->SetLoadingEnabled(false);
+      }
+
+      FixupAttribute(*aNodeOut, "src");
+
+      nsAutoString valueStr;
+      constexpr auto valueAttr = u"value"_ns;
+      // Update element node attributes with user-entered form state
+      RefPtr<dom::HTMLInputElement> outElt =
+          dom::HTMLInputElement::FromNode((*aNodeOut)->AsContent());
+      nsCOMPtr<nsIFormControl> formControl = do_QueryInterface(*aNodeOut);
+      switch (formControl->ControlType()) {
+        case FormControlType::InputEmail:
+        case FormControlType::InputSearch:
+        case FormControlType::InputText:
+        case FormControlType::InputTel:
+        case FormControlType::InputUrl:
+        case FormControlType::InputNumber:
+        case FormControlType::InputRange:
+        case FormControlType::InputDate:
+        case FormControlType::InputTime:
+        case FormControlType::InputColor:
+          nodeAsInput->GetValue(valueStr, dom::CallerType::System);
+          // Avoid superfluous value="" serialization
+          if (valueStr.IsEmpty()) {
+            outElt->RemoveAttribute(valueAttr, IgnoreErrors());
+          } else {
+            outElt->SetAttribute(valueAttr, valueStr, IgnoreErrors());
+          }
+          break;
+        case FormControlType::InputCheckbox:
+        case FormControlType::InputRadio:
+          outElt->SetDefaultChecked(nodeAsInput->Checked(), IgnoreErrors());
+          break;
+        default:
+          break;
+      }
+    }
+    return rv;
+  }
+
+  dom::HTMLTextAreaElement* nodeAsTextArea =
+      dom::HTMLTextAreaElement::FromNode(content);
+  if (nodeAsTextArea) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      // Tell the document encoder to serialize the text child we create below
+      *aSerializeCloneKids = true;
+
+      nsAutoString valueStr;
+      nodeAsTextArea->GetValue(valueStr);
+
+      (*aNodeOut)->SetTextContent(valueStr, IgnoreErrors());
+    }
+    return rv;
+  }
+
+  dom::HTMLOptionElement* nodeAsOption =
+      dom::HTMLOptionElement::FromNode(content);
+  if (nodeAsOption) {
+    nsresult rv = GetNodeToFixup(aNodeIn, aNodeOut);
+    if (NS_SUCCEEDED(rv) && *aNodeOut) {
+      dom::HTMLOptionElement* outElt =
+          dom::HTMLOptionElement::FromNode((*aNodeOut)->AsContent());
+      bool selected = nodeAsOption->Selected();
+      outElt->SetDefaultSelected(selected, IgnoreErrors());
+    }
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+}  // unnamed namespace
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::ReadResources(
+    nsIWebBrowserPersistResourceVisitor* aVisitor) {
+  nsresult rv = NS_OK;
+  nsCOMPtr<nsIWebBrowserPersistResourceVisitor> visitor = aVisitor;
+
+  NS_ENSURE_TRUE(mDocument, NS_ERROR_FAILURE);
+
+  ErrorResult err;
+  RefPtr<dom::TreeWalker> walker = mDocument->CreateTreeWalker(
+      *mDocument,
+      dom::NodeFilter_Binding::SHOW_ELEMENT |
+          dom::NodeFilter_Binding::SHOW_DOCUMENT |
+          dom::NodeFilter_Binding::SHOW_PROCESSING_INSTRUCTION,
+      nullptr, err);
+
+  if (NS_WARN_IF(err.Failed())) {
+    return err.StealNSResult();
+  }
+  MOZ_ASSERT(walker);
+
+  RefPtr<ResourceReader> reader = new ResourceReader(this, aVisitor);
+  nsCOMPtr<nsINode> currentNode = walker->CurrentNode();
+  do {
+    rv = reader->OnWalkDOMNode(currentNode);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      break;
+    }
+
+    ErrorResult err;
+    currentNode = walker->NextNode(err);
+    if (NS_WARN_IF(err.Failed())) {
+      err.SuppressException();
+      break;
+    }
+  } while (currentNode);
+  reader->DocumentDone(rv);
+  // If NS_FAILED(rv), it was / will be reported by an EndVisit call
+  // via DocumentDone.  This method must return a failure if and
+  // only if visitor won't be invoked.
+  return NS_OK;
+}
+
+static uint32_t ConvertEncoderFlags(uint32_t aEncoderFlags) {
+  uint32_t encoderFlags = 0;
+
+  if (aEncoderFlags & nsIWebBrowserPersist::ENCODE_FLAGS_SELECTION_ONLY)
+    encoderFlags |= nsIDocumentEncoder::OutputSelectionOnly;
+  if (aEncoderFlags & nsIWebBrowserPersist::ENCODE_FLAGS_FORMATTED)
+    encoderFlags |= nsIDocumentEncoder::OutputFormatted;
+  if (aEncoderFlags & nsIWebBrowserPersist::ENCODE_FLAGS_RAW)
+    encoderFlags |= nsIDocumentEncoder::OutputRaw;
+  if (aEncoderFlags & nsIWebBrowserPersist::ENCODE_FLAGS_BODY_ONLY)
+    encoderFlags |= nsIDocumentEncoder::OutputBodyOnly;
+  if (aEncoderFlags & nsIWebBrowserPersist::ENCODE_FLAGS_PREFORMATTED)
+    encoderFlags |= nsIDocumentEncoder::OutputPreformatted;
+  if (aEncoderFlags & nsIWebBrowserPersist::ENCODE_FLAGS_WRAP)
+    encoderFlags |= nsIDocumentEncoder::OutputWrap;
+  if (aEncoderFlags & nsIWebBrowserPersist::ENCODE_FLAGS_FORMAT_FLOWED)
+    encoderFlags |= nsIDocumentEncoder::OutputFormatFlowed;
+  if (aEncoderFlags & nsIWebBrowserPersist::ENCODE_FLAGS_ABSOLUTE_LINKS)
+    encoderFlags |= nsIDocumentEncoder::OutputAbsoluteLinks;
+  if (aEncoderFlags & nsIWebBrowserPersist::ENCODE_FLAGS_ENCODE_BASIC_ENTITIES)
+    encoderFlags |= nsIDocumentEncoder::OutputEncodeBasicEntities;
+  if (aEncoderFlags & nsIWebBrowserPersist::ENCODE_FLAGS_CR_LINEBREAKS)
+    encoderFlags |= nsIDocumentEncoder::OutputCRLineBreak;
+  if (aEncoderFlags & nsIWebBrowserPersist::ENCODE_FLAGS_LF_LINEBREAKS)
+    encoderFlags |= nsIDocumentEncoder::OutputLFLineBreak;
+  if (aEncoderFlags & nsIWebBrowserPersist::ENCODE_FLAGS_NOSCRIPT_CONTENT)
+    encoderFlags |= nsIDocumentEncoder::OutputNoScriptContent;
+  if (aEncoderFlags & nsIWebBrowserPersist::ENCODE_FLAGS_NOFRAMES_CONTENT)
+    encoderFlags |= nsIDocumentEncoder::OutputNoFramesContent;
+
+  return encoderFlags;
+}
+
+static bool ContentTypeEncoderExists(const nsACString& aType) {
+  return do_getDocumentTypeSupportedForEncoding(
+      PromiseFlatCString(aType).get());
+}
+
+void WebBrowserPersistLocalDocument::DecideContentType(
+    nsACString& aContentType) {
+  if (aContentType.IsEmpty()) {
+    if (NS_WARN_IF(NS_FAILED(GetContentType(aContentType)))) {
+      aContentType.Truncate();
+    }
+  }
+  if (!aContentType.IsEmpty() && !ContentTypeEncoderExists(aContentType)) {
+    aContentType.Truncate();
+  }
+  if (aContentType.IsEmpty()) {
+    aContentType.AssignLiteral("text/html");
+  }
+}
+
+nsresult WebBrowserPersistLocalDocument::GetDocEncoder(
+    const nsACString& aContentType, uint32_t aEncoderFlags,
+    nsIDocumentEncoder** aEncoder) {
+  nsCOMPtr<nsIDocumentEncoder> encoder =
+      do_createDocumentEncoder(PromiseFlatCString(aContentType).get());
+  NS_ENSURE_TRUE(encoder, NS_ERROR_FAILURE);
+
+  nsresult rv =
+      encoder->NativeInit(mDocument, NS_ConvertASCIItoUTF16(aContentType),
+                          ConvertEncoderFlags(aEncoderFlags));
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+
+  nsAutoCString charSet;
+  rv = GetCharacterSet(charSet);
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+  rv = encoder->SetCharset(charSet);
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+
+  encoder.forget(aEncoder);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistLocalDocument::WriteContent(
+    nsIOutputStream* aStream, nsIWebBrowserPersistURIMap* aMap,
+    const nsACString& aRequestedContentType, uint32_t aEncoderFlags,
+    uint32_t aWrapColumn, nsIWebBrowserPersistWriteCompletion* aCompletion) {
+  NS_ENSURE_ARG_POINTER(aStream);
+  NS_ENSURE_ARG_POINTER(aCompletion);
+  nsAutoCString contentType(aRequestedContentType);
+  DecideContentType(contentType);
+
+  nsCOMPtr<nsIDocumentEncoder> encoder;
+  nsresult rv =
+      GetDocEncoder(contentType, aEncoderFlags, getter_AddRefs(encoder));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (aWrapColumn != 0 &&
+      (aEncoderFlags & nsIWebBrowserPersist::ENCODE_FLAGS_WRAP)) {
+    encoder->SetWrapColumn(aWrapColumn);
+  }
+
+  nsCOMPtr<nsIURI> targetURI;
+  if (aMap) {
+    nsAutoCString targetURISpec;
+    rv = aMap->GetTargetBaseURI(targetURISpec);
+    if (NS_SUCCEEDED(rv) && !targetURISpec.IsEmpty()) {
+      rv = NS_NewURI(getter_AddRefs(targetURI), targetURISpec);
+      NS_ENSURE_SUCCESS(rv, NS_ERROR_UNEXPECTED);
+    } else if (mPersistFlags &
+               nsIWebBrowserPersist::PERSIST_FLAGS_FIXUP_LINKS_TO_DESTINATION) {
+      return NS_ERROR_UNEXPECTED;
+    }
+  }
+  rv = encoder->SetNodeFixup(new PersistNodeFixup(this, aMap, targetURI));
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+
+  rv = encoder->EncodeToStream(aStream);
+  aCompletion->OnFinish(this, aStream, contentType, rv);
+  return NS_OK;
+}
+
+}  // namespace mozilla
diff --git a/dom/webbrowserpersist/WebBrowserPersistLocalDocument.h b/dom/webbrowserpersist/WebBrowserPersistLocalDocument.h
new file mode 100644
index 0000000000..c1af8acd54
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistLocalDocument.h
@@ -0,0 +1,52 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 WebBrowserPersistLocalDocument_h__
+#define WebBrowserPersistLocalDocument_h__
+
+#include "mozilla/NotNull.h"
+#include "nsCOMPtr.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsIURI.h"
+#include "nsIWebBrowserPersistDocument.h"
+
+class nsIDocumentEncoder;
+class nsISHEntry;
+
+namespace mozilla {
+
+namespace dom {
+class Document;
+}
+
+class WebBrowserPersistLocalDocument final
+    : public nsIWebBrowserPersistDocument {
+ public:
+  explicit WebBrowserPersistLocalDocument(dom::Document* aDocument);
+
+  NotNull<const Encoding*> GetCharacterSet() const;
+  uint32_t GetPersistFlags() const;
+  nsIURI* GetBaseURI() const;
+
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_NSIWEBBROWSERPERSISTDOCUMENT
+
+  NS_DECL_CYCLE_COLLECTION_CLASS(WebBrowserPersistLocalDocument)
+
+ private:
+  RefPtr<dom::Document> mDocument;
+  uint32_t mPersistFlags;
+
+  void DecideContentType(nsACString& aContentType);
+  nsresult GetDocEncoder(const nsACString& aContentType, uint32_t aEncoderFlags,
+                         nsIDocumentEncoder** aEncoder);
+
+  virtual ~WebBrowserPersistLocalDocument();
+};
+
+}  // namespace mozilla
+
+#endif  // WebBrowserPersistLocalDocument_h__
diff --git a/dom/webbrowserpersist/WebBrowserPersistRemoteDocument.cpp b/dom/webbrowserpersist/WebBrowserPersistRemoteDocument.cpp
new file mode 100644
index 0000000000..a4e7c96c85
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistRemoteDocument.cpp
@@ -0,0 +1,207 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 "WebBrowserPersistRemoteDocument.h"
+#include "WebBrowserPersistDocumentParent.h"
+#include "WebBrowserPersistResourcesParent.h"
+#include "WebBrowserPersistSerializeParent.h"
+#include "mozilla/Unused.h"
+#include "mozilla/ipc/BackgroundUtils.h"
+#include "mozilla/net/CookieJarSettings.h"
+
+#include "nsDebug.h"
+#include "nsIPrincipal.h"
+#include "nsISHEntry.h"
+
+namespace mozilla {
+
+NS_IMPL_ISUPPORTS(WebBrowserPersistRemoteDocument, nsIWebBrowserPersistDocument)
+
+WebBrowserPersistRemoteDocument ::WebBrowserPersistRemoteDocument(
+    WebBrowserPersistDocumentParent* aActor, const Attrs& aAttrs,
+    nsIInputStream* aPostData)
+    : mActor(aActor), mAttrs(aAttrs), mPostData(aPostData) {
+  auto principalOrErr = ipc::PrincipalInfoToPrincipal(mAttrs.principal());
+  if (principalOrErr.isOk()) {
+    mPrincipal = principalOrErr.unwrap();
+  } else {
+    NS_WARNING("Failed to obtain principal!");
+  }
+
+  net::CookieJarSettings::Deserialize(mAttrs.cookieJarSettings(),
+                                      getter_AddRefs(mCookieJarSettings));
+}
+
+WebBrowserPersistRemoteDocument::~WebBrowserPersistRemoteDocument() {
+  if (mActor) {
+    Unused << WebBrowserPersistDocumentParent::Send__delete__(mActor);
+    // That will call mActor->ActorDestroy, which calls this->ActorDestroy
+    // (whether or not the IPC send succeeds).
+  }
+  MOZ_ASSERT(!mActor);
+}
+
+void WebBrowserPersistRemoteDocument::ActorDestroy(void) { mActor = nullptr; }
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::GetIsClosed(bool* aIsClosed) {
+  *aIsClosed = !mActor;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::GetIsPrivate(bool* aIsPrivate) {
+  *aIsPrivate = mAttrs.isPrivate();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::GetDocumentURI(nsACString& aURISpec) {
+  aURISpec = mAttrs.documentURI();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::GetBaseURI(nsACString& aURISpec) {
+  aURISpec = mAttrs.baseURI();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::GetContentType(nsACString& aContentType) {
+  aContentType = mAttrs.contentType();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::GetCharacterSet(nsACString& aCharSet) {
+  aCharSet = mAttrs.characterSet();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::GetTitle(nsAString& aTitle) {
+  aTitle = mAttrs.title();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::GetReferrerInfo(
+    nsIReferrerInfo** aReferrerInfo) {
+  *aReferrerInfo = mAttrs.referrerInfo();
+  NS_IF_ADDREF(*aReferrerInfo);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::GetCookieJarSettings(
+    nsICookieJarSettings** aCookieJarSettings) {
+  nsCOMPtr<nsICookieJarSettings> cookieJarSettings = mCookieJarSettings;
+  cookieJarSettings.forget(aCookieJarSettings);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::GetContentDisposition(nsAString& aDisp) {
+  aDisp = mAttrs.contentDisposition();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::GetCacheKey(uint32_t* aCacheKey) {
+  *aCacheKey = mAttrs.sessionHistoryCacheKey();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::GetPersistFlags(uint32_t* aFlags) {
+  *aFlags = mAttrs.persistFlags();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::SetPersistFlags(uint32_t aFlags) {
+  if (!mActor) {
+    return NS_ERROR_FAILURE;
+  }
+  if (!mActor->SendSetPersistFlags(aFlags)) {
+    return NS_ERROR_FAILURE;
+  }
+  mAttrs.persistFlags() = aFlags;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::GetPostData(nsIInputStream** aStream) {
+  nsCOMPtr<nsIInputStream> stream = mPostData;
+  stream.forget(aStream);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::GetPrincipal(nsIPrincipal** aPrincipal) {
+  nsCOMPtr<nsIPrincipal> nodePrincipal = mPrincipal;
+  nodePrincipal.forget(aPrincipal);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::ReadResources(
+    nsIWebBrowserPersistResourceVisitor* aVisitor) {
+  if (!mActor) {
+    return NS_ERROR_FAILURE;
+  }
+  RefPtr<WebBrowserPersistResourcesParent> subActor =
+      new WebBrowserPersistResourcesParent(this, aVisitor);
+  return mActor->SendPWebBrowserPersistResourcesConstructor(
+             subActor.forget().take())
+             ? NS_OK
+             : NS_ERROR_FAILURE;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistRemoteDocument::WriteContent(
+    nsIOutputStream* aStream, nsIWebBrowserPersistURIMap* aMap,
+    const nsACString& aRequestedContentType, uint32_t aEncoderFlags,
+    uint32_t aWrapColumn, nsIWebBrowserPersistWriteCompletion* aCompletion) {
+  if (!mActor) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsresult rv;
+  WebBrowserPersistURIMap map;
+  uint32_t numMappedURIs;
+  if (aMap) {
+    rv = aMap->GetTargetBaseURI(map.targetBaseURI());
+    NS_ENSURE_SUCCESS(rv, rv);
+    rv = aMap->GetNumMappedURIs(&numMappedURIs);
+    NS_ENSURE_SUCCESS(rv, rv);
+    for (uint32_t i = 0; i < numMappedURIs; ++i) {
+      WebBrowserPersistURIMapEntry& nextEntry =
+          *(map.mapURIs().AppendElement());
+      rv = aMap->GetURIMapping(i, nextEntry.mapFrom(), nextEntry.mapTo());
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+  }
+
+  auto* subActor =
+      new WebBrowserPersistSerializeParent(this, aStream, aCompletion);
+  nsCString requestedContentType(aRequestedContentType);  // Sigh.
+  return mActor->SendPWebBrowserPersistSerializeConstructor(
+             subActor, map, requestedContentType, aEncoderFlags, aWrapColumn)
+             ? NS_OK
+             : NS_ERROR_FAILURE;
+}
+
+// Forcing WebBrowserPersistRemoteDocument to implement GetHistory is the
+// easiest way to ensure that we can call GetHistory in
+// WebBrowserPersistDocumentChild::Start
+already_AddRefed<nsISHEntry> WebBrowserPersistRemoteDocument::GetHistory() {
+  MOZ_CRASH("We should not call GetHistory on WebBrowserPersistRemoteDocument");
+  return nullptr;
+}
+
+}  // namespace mozilla
diff --git a/dom/webbrowserpersist/WebBrowserPersistRemoteDocument.h b/dom/webbrowserpersist/WebBrowserPersistRemoteDocument.h
new file mode 100644
index 0000000000..e33976b3d2
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistRemoteDocument.h
@@ -0,0 +1,59 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 WebBrowserPersistRemoteDocument_h__
+#define WebBrowserPersistRemoteDocument_h__
+
+#include "mozilla/Maybe.h"
+#include "mozilla/PWebBrowserPersistDocumentParent.h"
+#include "nsCOMPtr.h"
+#include "nsIWebBrowserPersistDocument.h"
+#include "nsIInputStream.h"
+
+class nsIPrincipal;
+
+// This class is the XPCOM half of the glue between the
+// nsIWebBrowserPersistDocument interface and a remote document; it is
+// created by WebBrowserPersistDocumentParent when (and if) it
+// receives the information needed to populate the interface's
+// properties.
+//
+// This object has a normal refcounted lifetime.  The corresponding
+// IPC actor holds a weak reference to this class; when the last
+// strong reference is released, it sends an IPC delete message and
+// thereby removes that reference.
+
+namespace mozilla {
+
+class WebBrowserPersistDocumentParent;
+
+class WebBrowserPersistRemoteDocument final
+    : public nsIWebBrowserPersistDocument {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIWEBBROWSERPERSISTDOCUMENT
+
+ private:
+  using Attrs = WebBrowserPersistDocumentAttrs;
+  WebBrowserPersistDocumentParent* mActor;
+  Attrs mAttrs;
+  nsCOMPtr<nsISHEntry> mSHEntry;
+  nsCOMPtr<nsICookieJarSettings> mCookieJarSettings;
+  nsCOMPtr<nsIInputStream> mPostData;
+  nsCOMPtr<nsIPrincipal> mPrincipal;
+
+  friend class WebBrowserPersistDocumentParent;
+  WebBrowserPersistRemoteDocument(WebBrowserPersistDocumentParent* aActor,
+                                  const Attrs& aAttrs,
+                                  nsIInputStream* aPostData);
+  ~WebBrowserPersistRemoteDocument();
+
+  void ActorDestroy(void);
+};
+
+}  // namespace mozilla
+
+#endif  // WebBrowserPersistRemoteDocument_h__
diff --git a/dom/webbrowserpersist/WebBrowserPersistResourcesChild.cpp b/dom/webbrowserpersist/WebBrowserPersistResourcesChild.cpp
new file mode 100644
index 0000000000..b77b8fe25a
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistResourcesChild.cpp
@@ -0,0 +1,76 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 "WebBrowserPersistResourcesChild.h"
+
+#include "WebBrowserPersistDocumentChild.h"
+#include "mozilla/dom/PContentChild.h"
+
+namespace mozilla {
+
+NS_IMPL_ISUPPORTS(WebBrowserPersistResourcesChild,
+                  nsIWebBrowserPersistResourceVisitor)
+
+WebBrowserPersistResourcesChild::WebBrowserPersistResourcesChild() = default;
+
+WebBrowserPersistResourcesChild::~WebBrowserPersistResourcesChild() = default;
+
+NS_IMETHODIMP
+WebBrowserPersistResourcesChild::VisitResource(
+    nsIWebBrowserPersistDocument* aDocument, const nsACString& aURI,
+    nsContentPolicyType aContentPolicyType) {
+  nsCString copiedURI(aURI);  // Yay, XPIDL/IPDL mismatch.
+  SendVisitResource(copiedURI, aContentPolicyType);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistResourcesChild::VisitDocument(
+    nsIWebBrowserPersistDocument* aDocument,
+    nsIWebBrowserPersistDocument* aSubDocument) {
+  auto* subActor = new WebBrowserPersistDocumentChild();
+  // As a consequence of how PWebBrowserPersistDocumentConstructor
+  // can be sent by both the parent and the child, we must pass the
+  // aBrowser and outerWindowID arguments here, but the values are
+  // ignored by the parent.  In particular, the BrowserChild in which
+  // persistence started does not necessarily exist at this point;
+  // see bug 1203602.
+  if (!Manager()->Manager()->SendPWebBrowserPersistDocumentConstructor(
+          subActor, nullptr, nullptr)) {
+    // NOTE: subActor is freed at this point.
+    return NS_ERROR_FAILURE;
+  }
+  // ...but here, IPC won't free subActor until after this returns
+  // to the event loop.
+
+  // The order of these two messages will be preserved, because
+  // they're the same toplevel protocol and priority.
+  //
+  // With this ordering, it's always the transition out of START
+  // state that causes a document's parent actor to be exposed to
+  // XPCOM (for both parent->child and child->parent construction),
+  // which simplifies the lifetime management.
+  SendVisitDocument(subActor);
+  subActor->Start(aSubDocument);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistResourcesChild::VisitBrowsingContext(
+    nsIWebBrowserPersistDocument* aDocument,
+    dom::BrowsingContext* aBrowsingContext) {
+  SendVisitBrowsingContext(aBrowsingContext);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistResourcesChild::EndVisit(
+    nsIWebBrowserPersistDocument* aDocument, nsresult aStatus) {
+  Send__delete__(this, aStatus);
+  return NS_OK;
+}
+
+}  // namespace mozilla
diff --git a/dom/webbrowserpersist/WebBrowserPersistResourcesChild.h b/dom/webbrowserpersist/WebBrowserPersistResourcesChild.h
new file mode 100644
index 0000000000..ff0a11ee8f
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistResourcesChild.h
@@ -0,0 +1,30 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 WebBrowserPersistResourcesChild_h__
+#define WebBrowserPersistResourcesChild_h__
+
+#include "mozilla/PWebBrowserPersistResourcesChild.h"
+
+#include "nsIWebBrowserPersistDocument.h"
+
+namespace mozilla {
+
+class WebBrowserPersistResourcesChild final
+    : public PWebBrowserPersistResourcesChild,
+      public nsIWebBrowserPersistResourceVisitor {
+ public:
+  WebBrowserPersistResourcesChild();
+
+  NS_DECL_NSIWEBBROWSERPERSISTRESOURCEVISITOR
+  NS_DECL_ISUPPORTS
+ private:
+  virtual ~WebBrowserPersistResourcesChild();
+};
+
+}  // namespace mozilla
+
+#endif  // WebBrowserPersistDocumentChild_h__
diff --git a/dom/webbrowserpersist/WebBrowserPersistResourcesParent.cpp b/dom/webbrowserpersist/WebBrowserPersistResourcesParent.cpp
new file mode 100644
index 0000000000..2ebfb4b28e
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistResourcesParent.cpp
@@ -0,0 +1,94 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 "WebBrowserPersistResourcesParent.h"
+
+#include "nsThreadUtils.h"
+
+#include "mozilla/dom/BrowserParent.h"
+#include "mozilla/dom/CanonicalBrowsingContext.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/dom/WindowGlobalParent.h"
+
+namespace mozilla {
+
+NS_IMPL_ISUPPORTS(WebBrowserPersistResourcesParent,
+                  nsIWebBrowserPersistDocumentReceiver)
+
+WebBrowserPersistResourcesParent::WebBrowserPersistResourcesParent(
+    nsIWebBrowserPersistDocument* aDocument,
+    nsIWebBrowserPersistResourceVisitor* aVisitor)
+    : mDocument(aDocument), mVisitor(aVisitor) {
+  MOZ_ASSERT(aDocument);
+  MOZ_ASSERT(aVisitor);
+}
+
+WebBrowserPersistResourcesParent::~WebBrowserPersistResourcesParent() = default;
+
+void WebBrowserPersistResourcesParent::ActorDestroy(ActorDestroyReason aWhy) {
+  if (aWhy != Deletion && mVisitor) {
+    // See comment in WebBrowserPersistDocumentParent::ActorDestroy
+    // (or bug 1202887) for why this is deferred.
+    nsCOMPtr<nsIRunnable> errorLater =
+        NewRunnableMethod<nsCOMPtr<nsIWebBrowserPersistDocument>, nsresult>(
+            "nsIWebBrowserPersistResourceVisitor::EndVisit", mVisitor,
+            &nsIWebBrowserPersistResourceVisitor::EndVisit, mDocument,
+            NS_ERROR_FAILURE);
+    NS_DispatchToCurrentThread(errorLater);
+  }
+  mVisitor = nullptr;
+}
+
+mozilla::ipc::IPCResult WebBrowserPersistResourcesParent::Recv__delete__(
+    const nsresult& aStatus) {
+  mVisitor->EndVisit(mDocument, aStatus);
+  mVisitor = nullptr;
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult WebBrowserPersistResourcesParent::RecvVisitResource(
+    const nsACString& aURI, const nsContentPolicyType& aContentPolicyType) {
+  mVisitor->VisitResource(mDocument, aURI, aContentPolicyType);
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult WebBrowserPersistResourcesParent::RecvVisitDocument(
+    PWebBrowserPersistDocumentParent* aSubDocument) {
+  // Don't expose the subdocument to the visitor until it's ready
+  // (until the actor isn't in START state).
+  static_cast<WebBrowserPersistDocumentParent*>(aSubDocument)->SetOnReady(this);
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult
+WebBrowserPersistResourcesParent::RecvVisitBrowsingContext(
+    const dom::MaybeDiscarded<dom::BrowsingContext>& aContext) {
+  if (aContext.IsNullOrDiscarded()) {
+    // Nothing useful to do but ignore the discarded context.
+    return IPC_OK();
+  }
+
+  mVisitor->VisitBrowsingContext(mDocument, aContext.get());
+  return IPC_OK();
+}
+
+NS_IMETHODIMP
+WebBrowserPersistResourcesParent::OnDocumentReady(
+    nsIWebBrowserPersistDocument* aSubDocument) {
+  if (!mVisitor) {
+    return NS_ERROR_FAILURE;
+  }
+  mVisitor->VisitDocument(mDocument, aSubDocument);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistResourcesParent::OnError(nsresult aFailure) {
+  // Nothing useful to do but ignore the failed document.
+  return NS_OK;
+}
+
+}  // namespace mozilla
diff --git a/dom/webbrowserpersist/WebBrowserPersistResourcesParent.h b/dom/webbrowserpersist/WebBrowserPersistResourcesParent.h
new file mode 100644
index 0000000000..fce0a59d97
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistResourcesParent.h
@@ -0,0 +1,57 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 WebBrowserPersistResourcesParent_h__
+#define WebBrowserPersistResourcesParent_h__
+
+#include "mozilla/PWebBrowserPersistResourcesParent.h"
+
+#include "WebBrowserPersistDocumentParent.h"
+#include "nsCOMPtr.h"
+#include "nsIWebBrowserPersistDocument.h"
+
+namespace mozilla {
+
+class WebBrowserPersistResourcesParent final
+    : public PWebBrowserPersistResourcesParent,
+      public nsIWebBrowserPersistDocumentReceiver {
+ public:
+  WebBrowserPersistResourcesParent(
+      nsIWebBrowserPersistDocument* aDocument,
+      nsIWebBrowserPersistResourceVisitor* aVisitor);
+
+  virtual mozilla::ipc::IPCResult RecvVisitResource(
+      const nsACString& aURI,
+      const nsContentPolicyType& aContentPolicyType) override;
+
+  virtual mozilla::ipc::IPCResult RecvVisitDocument(
+      PWebBrowserPersistDocumentParent* aSubDocument) override;
+
+  virtual mozilla::ipc::IPCResult RecvVisitBrowsingContext(
+      const dom::MaybeDiscarded<dom::BrowsingContext>& aContext) override;
+
+  virtual mozilla::ipc::IPCResult Recv__delete__(
+      const nsresult& aStatus) override;
+
+  virtual void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  NS_DECL_NSIWEBBROWSERPERSISTDOCUMENTRECEIVER
+  NS_DECL_ISUPPORTS
+
+ private:
+  // Note: even if the XPIDL didn't need mDocument for visitor
+  // callbacks, this object still needs to hold a strong reference
+  // to it to defer actor subtree deletion until after the
+  // visitation is finished.
+  nsCOMPtr<nsIWebBrowserPersistDocument> mDocument;
+  nsCOMPtr<nsIWebBrowserPersistResourceVisitor> mVisitor;
+
+  virtual ~WebBrowserPersistResourcesParent();
+};
+
+}  // namespace mozilla
+
+#endif  // WebBrowserPersistResourcesParent_h__
diff --git a/dom/webbrowserpersist/WebBrowserPersistSerializeChild.cpp b/dom/webbrowserpersist/WebBrowserPersistSerializeChild.cpp
new file mode 100644
index 0000000000..cdfb2d8472
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistSerializeChild.cpp
@@ -0,0 +1,130 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 "WebBrowserPersistSerializeChild.h"
+
+#include <algorithm>
+
+#include "nsThreadUtils.h"
+
+namespace mozilla {
+
+NS_IMPL_ISUPPORTS(WebBrowserPersistSerializeChild,
+                  nsIWebBrowserPersistWriteCompletion,
+                  nsIWebBrowserPersistURIMap, nsIOutputStream)
+
+WebBrowserPersistSerializeChild::WebBrowserPersistSerializeChild(
+    const WebBrowserPersistURIMap& aMap)
+    : mMap(aMap) {}
+
+WebBrowserPersistSerializeChild::~WebBrowserPersistSerializeChild() = default;
+
+NS_IMETHODIMP
+WebBrowserPersistSerializeChild::OnFinish(
+    nsIWebBrowserPersistDocument* aDocument, nsIOutputStream* aStream,
+    const nsACString& aContentType, nsresult aStatus) {
+  MOZ_ASSERT(aStream == this);
+  nsCString contentType(aContentType);
+  Send__delete__(this, contentType, aStatus);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistSerializeChild::GetNumMappedURIs(uint32_t* aNum) {
+  *aNum = static_cast<uint32_t>(mMap.mapURIs().Length());
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistSerializeChild::GetURIMapping(uint32_t aIndex,
+                                               nsACString& aMapFrom,
+                                               nsACString& aMapTo) {
+  if (aIndex >= mMap.mapURIs().Length()) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  aMapFrom = mMap.mapURIs()[aIndex].mapFrom();
+  aMapTo = mMap.mapURIs()[aIndex].mapTo();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistSerializeChild::GetTargetBaseURI(nsACString& aURI) {
+  aURI = mMap.targetBaseURI();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistSerializeChild::Close() {
+  NS_WARNING("WebBrowserPersistSerializeChild::Close()");
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistSerializeChild::Flush() {
+  NS_WARNING("WebBrowserPersistSerializeChild::Flush()");
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistSerializeChild::Write(const char* aBuf, uint32_t aCount,
+                                       uint32_t* aWritten) {
+  // Normally an nsIOutputStream would have to be thread-safe, but
+  // nsDocumentEncoder currently doesn't call this off the main
+  // thread (which also means it's difficult to test the
+  // thread-safety code this class doesn't yet have).
+  //
+  // This is *not* an NS_ERROR_NOT_IMPLEMENTED, because at this
+  // point we've probably already misused the non-thread-safe
+  // refcounting.
+  MOZ_RELEASE_ASSERT(NS_IsMainThread(), "Fix this class to be thread-safe.");
+
+  // Limit the message size to 64k because large messages are
+  // potentially bad for the latency of other messages on the same channel.
+  static const uint32_t kMaxWrite = 65536;
+
+  // Work around bug 1181433 by sending multiple messages if
+  // necessary to write the entire aCount bytes, even though
+  // nsIOutputStream.idl says we're allowed to do a short write.
+  const char* buf = aBuf;
+  uint32_t count = aCount;
+  *aWritten = 0;
+  while (count > 0) {
+    uint32_t toWrite = std::min(kMaxWrite, count);
+    nsTArray<uint8_t> arrayBuf;
+    // It would be nice if this extra copy could be avoided.
+    arrayBuf.AppendElements(buf, toWrite);
+    SendWriteData(std::move(arrayBuf));
+    *aWritten += toWrite;
+    buf += toWrite;
+    count -= toWrite;
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistSerializeChild::WriteFrom(nsIInputStream* aFrom,
+                                           uint32_t aCount,
+                                           uint32_t* aWritten) {
+  NS_WARNING("WebBrowserPersistSerializeChild::WriteFrom()");
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistSerializeChild::WriteSegments(nsReadSegmentFun aFun,
+                                               void* aCtx, uint32_t aCount,
+                                               uint32_t* aWritten) {
+  NS_WARNING("WebBrowserPersistSerializeChild::WriteSegments()");
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+WebBrowserPersistSerializeChild::IsNonBlocking(bool* aNonBlocking) {
+  // Writes will never fail with NS_BASE_STREAM_WOULD_BLOCK, so:
+  *aNonBlocking = false;
+  return NS_OK;
+}
+
+}  // namespace mozilla
diff --git a/dom/webbrowserpersist/WebBrowserPersistSerializeChild.h b/dom/webbrowserpersist/WebBrowserPersistSerializeChild.h
new file mode 100644
index 0000000000..86bcf0e1e7
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistSerializeChild.h
@@ -0,0 +1,38 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 WebBrowserPersistSerializeChild_h__
+#define WebBrowserPersistSerializeChild_h__
+
+#include "mozilla/PWebBrowserPersistSerializeChild.h"
+
+#include "mozilla/PWebBrowserPersistDocument.h"
+#include "nsIWebBrowserPersistDocument.h"
+#include "nsIOutputStream.h"
+
+namespace mozilla {
+
+class WebBrowserPersistSerializeChild final
+    : public PWebBrowserPersistSerializeChild,
+      public nsIWebBrowserPersistWriteCompletion,
+      public nsIWebBrowserPersistURIMap,
+      public nsIOutputStream {
+ public:
+  explicit WebBrowserPersistSerializeChild(const WebBrowserPersistURIMap& aMap);
+
+  NS_DECL_NSIWEBBROWSERPERSISTWRITECOMPLETION
+  NS_DECL_NSIWEBBROWSERPERSISTURIMAP
+  NS_DECL_NSIOUTPUTSTREAM
+  NS_DECL_ISUPPORTS
+ private:
+  WebBrowserPersistURIMap mMap;
+
+  virtual ~WebBrowserPersistSerializeChild();
+};
+
+}  // namespace mozilla
+
+#endif  // WebBrowserPersistSerializeChild_h__
diff --git a/dom/webbrowserpersist/WebBrowserPersistSerializeParent.cpp b/dom/webbrowserpersist/WebBrowserPersistSerializeParent.cpp
new file mode 100644
index 0000000000..1fe1af95ff
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistSerializeParent.cpp
@@ -0,0 +1,78 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 "WebBrowserPersistSerializeParent.h"
+
+#include "nsReadableUtils.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla {
+
+WebBrowserPersistSerializeParent::WebBrowserPersistSerializeParent(
+    nsIWebBrowserPersistDocument* aDocument, nsIOutputStream* aStream,
+    nsIWebBrowserPersistWriteCompletion* aFinish)
+    : mDocument(aDocument),
+      mStream(aStream),
+      mFinish(aFinish),
+      mOutputError(NS_OK) {
+  MOZ_ASSERT(aDocument);
+  MOZ_ASSERT(aStream);
+  MOZ_ASSERT(aFinish);
+}
+
+WebBrowserPersistSerializeParent::~WebBrowserPersistSerializeParent() = default;
+
+mozilla::ipc::IPCResult WebBrowserPersistSerializeParent::RecvWriteData(
+    nsTArray<uint8_t>&& aData) {
+  if (NS_FAILED(mOutputError)) {
+    return IPC_OK();
+  }
+
+  uint32_t written = 0;
+  static_assert(sizeof(char) == sizeof(uint8_t),
+                "char must be (at least?) 8 bits");
+  const char* data = reinterpret_cast<const char*>(aData.Elements());
+  // nsIOutputStream::Write is allowed to return short writes.
+  while (written < aData.Length()) {
+    uint32_t writeReturn;
+    nsresult rv =
+        mStream->Write(data + written, aData.Length() - written, &writeReturn);
+    if (NS_FAILED(rv)) {
+      mOutputError = rv;
+      return IPC_OK();
+    }
+    written += writeReturn;
+  }
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult WebBrowserPersistSerializeParent::Recv__delete__(
+    const nsACString& aContentType, const nsresult& aStatus) {
+  if (NS_SUCCEEDED(mOutputError)) {
+    mOutputError = aStatus;
+  }
+  mFinish->OnFinish(mDocument, mStream, aContentType, mOutputError);
+  mFinish = nullptr;
+  return IPC_OK();
+}
+
+void WebBrowserPersistSerializeParent::ActorDestroy(ActorDestroyReason aWhy) {
+  if (mFinish) {
+    MOZ_ASSERT(aWhy != Deletion);
+    // See comment in WebBrowserPersistDocumentParent::ActorDestroy
+    // (or bug 1202887) for why this is deferred.
+    nsCOMPtr<nsIRunnable> errorLater =
+        NewRunnableMethod<nsCOMPtr<nsIWebBrowserPersistDocument>,
+                          nsCOMPtr<nsIOutputStream>, nsCString, nsresult>(
+            "nsIWebBrowserPersistWriteCompletion::OnFinish", mFinish,
+            &nsIWebBrowserPersistWriteCompletion::OnFinish, mDocument, mStream,
+            ""_ns, NS_ERROR_FAILURE);
+    NS_DispatchToCurrentThread(errorLater);
+    mFinish = nullptr;
+  }
+}
+
+}  // namespace mozilla
diff --git a/dom/webbrowserpersist/WebBrowserPersistSerializeParent.h b/dom/webbrowserpersist/WebBrowserPersistSerializeParent.h
new file mode 100644
index 0000000000..56bd789c55
--- /dev/null
+++ b/dom/webbrowserpersist/WebBrowserPersistSerializeParent.h
@@ -0,0 +1,45 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 WebBrowserPersistSerializeParent_h__
+#define WebBrowserPersistSerializeParent_h__
+
+#include "mozilla/PWebBrowserPersistSerializeParent.h"
+
+#include "nsCOMPtr.h"
+#include "nsIOutputStream.h"
+#include "nsIWebBrowserPersistDocument.h"
+
+namespace mozilla {
+
+class WebBrowserPersistSerializeParent
+    : public PWebBrowserPersistSerializeParent {
+ public:
+  WebBrowserPersistSerializeParent(
+      nsIWebBrowserPersistDocument* aDocument, nsIOutputStream* aStream,
+      nsIWebBrowserPersistWriteCompletion* aFinish);
+  virtual ~WebBrowserPersistSerializeParent();
+
+  virtual mozilla::ipc::IPCResult RecvWriteData(
+      nsTArray<uint8_t>&& aData) override;
+
+  virtual mozilla::ipc::IPCResult Recv__delete__(
+      const nsACString& aContentType, const nsresult& aStatus) override;
+
+  virtual void ActorDestroy(ActorDestroyReason aWhy) override;
+
+ private:
+  // See also ...ReadParent::mDocument for the other reason this
+  // strong reference needs to be here.
+  nsCOMPtr<nsIWebBrowserPersistDocument> mDocument;
+  nsCOMPtr<nsIOutputStream> mStream;
+  nsCOMPtr<nsIWebBrowserPersistWriteCompletion> mFinish;
+  nsresult mOutputError;
+};
+
+}  // namespace mozilla
+
+#endif  // WebBrowserPersistSerializeParent_h__
diff --git a/dom/webbrowserpersist/moz.build b/dom/webbrowserpersist/moz.build
new file mode 100644
index 0000000000..2c3e6a4d0f
--- /dev/null
+++ b/dom/webbrowserpersist/moz.build
@@ -0,0 +1,49 @@
+# -*- 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/.
+
+# moved from embedding/components/webbrowserpersist Jan 13, 2017
+with Files("**"):
+    BUG_COMPONENT = ("Core", "DOM: Core & HTML")
+
+XPIDL_SOURCES += [
+    "nsIWebBrowserPersist.idl",
+    "nsIWebBrowserPersistDocument.idl",
+]
+
+XPIDL_MODULE = "webbrowserpersist"
+
+IPDL_SOURCES += [
+    "PWebBrowserPersistDocument.ipdl",
+    "PWebBrowserPersistResources.ipdl",
+    "PWebBrowserPersistSerialize.ipdl",
+]
+
+UNIFIED_SOURCES += [
+    "nsWebBrowserPersist.cpp",
+    "WebBrowserPersistDocumentChild.cpp",
+    "WebBrowserPersistDocumentParent.cpp",
+    "WebBrowserPersistLocalDocument.cpp",
+    "WebBrowserPersistRemoteDocument.cpp",
+    "WebBrowserPersistResourcesChild.cpp",
+    "WebBrowserPersistResourcesParent.cpp",
+    "WebBrowserPersistSerializeChild.cpp",
+    "WebBrowserPersistSerializeParent.cpp",
+]
+
+EXPORTS.mozilla += [
+    "WebBrowserPersistDocumentChild.h",
+    "WebBrowserPersistDocumentParent.h",
+    "WebBrowserPersistLocalDocument.h",
+]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+FINAL_LIBRARY = "xul"
+LOCAL_INCLUDES += [
+    "/docshell/shistory",
+    "/dom/base",
+    "/dom/html",
+]
diff --git a/dom/webbrowserpersist/nsIWebBrowserPersist.idl b/dom/webbrowserpersist/nsIWebBrowserPersist.idl
new file mode 100644
index 0000000000..0cfd021142
--- /dev/null
+++ b/dom/webbrowserpersist/nsIWebBrowserPersist.idl
@@ -0,0 +1,282 @@
+/* -*- Mode: IDL; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 "nsICancelable.idl"
+#include "nsIContentPolicy.idl"
+
+interface nsIURI;
+interface nsIInputStream;
+interface nsIWebProgressListener;
+interface nsIFile;
+interface nsIChannel;
+interface nsILoadContext;
+interface nsIPrincipal;
+interface nsIReferrerInfo;
+interface nsICookieJarSettings;
+
+/**
+ * Interface for persisting DOM documents and URIs to local or remote storage.
+ */
+[scriptable, uuid(8cd752a4-60b1-42c3-a819-65c7a1138a28)]
+interface nsIWebBrowserPersist : nsICancelable
+{
+  /** No special persistence behaviour. */
+  const unsigned long PERSIST_FLAGS_NONE = 0;
+  /** Use cached data if present (skipping validation), else load from network */
+  const unsigned long PERSIST_FLAGS_FROM_CACHE = 1;
+  /** Bypass the cached data. */
+  const unsigned long PERSIST_FLAGS_BYPASS_CACHE = 2;
+  /** Ignore any redirected data (usually adverts). */
+  const unsigned long PERSIST_FLAGS_IGNORE_REDIRECTED_DATA = 4;
+  /** Ignore IFRAME content (usually adverts). */
+  const unsigned long PERSIST_FLAGS_IGNORE_IFRAMES = 8;
+  /** Do not run the incoming data through a content converter e.g. to decompress it */
+  const unsigned long PERSIST_FLAGS_NO_CONVERSION = 16;
+  /** Replace existing files on the disk (use with due diligence!) */
+  const unsigned long PERSIST_FLAGS_REPLACE_EXISTING_FILES = 32;
+  /** Don't modify or add base tags */
+  const unsigned long PERSIST_FLAGS_NO_BASE_TAG_MODIFICATIONS = 64;
+  /** Make changes to original dom rather than cloning nodes */
+  const unsigned long PERSIST_FLAGS_FIXUP_ORIGINAL_DOM = 128;
+  /** Fix links relative to destination location (not origin) */
+  const unsigned long PERSIST_FLAGS_FIXUP_LINKS_TO_DESTINATION = 256;
+  /** Don't make any adjustments to links */
+  const unsigned long PERSIST_FLAGS_DONT_FIXUP_LINKS = 512;
+  /** Force serialization of output (one file at a time; not concurrent) */
+  const unsigned long PERSIST_FLAGS_SERIALIZE_OUTPUT = 1024;
+  /** Don't make any adjustments to filenames */
+  const unsigned long PERSIST_FLAGS_DONT_CHANGE_FILENAMES = 2048;
+  /** Fail on broken inline links */
+  const unsigned long PERSIST_FLAGS_FAIL_ON_BROKEN_LINKS = 4096;
+  /**
+   * Automatically cleanup after a failed or cancelled operation, deleting all
+   * created files and directories. This flag does nothing for failed upload
+   * operations to remote servers.
+   */
+  const unsigned long PERSIST_FLAGS_CLEANUP_ON_FAILURE = 8192;
+  /**
+   * Let the WebBrowserPersist decide whether the incoming data is encoded
+   * and whether it needs to go through a content converter e.g. to
+   * decompress it.
+   */
+  const unsigned long PERSIST_FLAGS_AUTODETECT_APPLY_CONVERSION = 16384;
+  /**
+   * Append the downloaded data to the target file.
+   * This can only be used when persisting to a local file.
+   */
+  const unsigned long PERSIST_FLAGS_APPEND_TO_FILE = 32768;
+
+  /**
+   * Flags governing how data is fetched and saved from the network.
+   * It is best to set this value explicitly unless you are prepared
+   * to accept the default values.
+   */
+  attribute unsigned long persistFlags;
+
+  /** Persister is ready to save data */
+  const unsigned long PERSIST_STATE_READY = 1;
+  /** Persister is saving data */
+  const unsigned long PERSIST_STATE_SAVING = 2;
+  /** Persister has finished saving data */
+  const unsigned long PERSIST_STATE_FINISHED = 3;
+
+  /**
+   * Current state of the persister object.
+   */
+  readonly attribute unsigned long currentState;
+
+  /**
+   * Value indicating the success or failure of the persist
+   * operation.
+   *
+   * @throws NS_BINDING_ABORTED Operation cancelled.
+   * @throws NS_ERROR_FAILURE Non-specific failure.
+   */
+  readonly attribute nsresult result;
+
+  /**
+   * Callback listener for progress notifications. The object that the
+   * embbedder supplies may also implement nsIInterfaceRequestor and be
+   * prepared to return nsIAuthPrompt or other interfaces that may be required
+   * to download data.
+   *
+   * @see nsIAuthPrompt
+   * @see nsIInterfaceRequestor
+   */
+  attribute nsIWebProgressListener progressListener;
+
+  /**
+   * Save the specified URI to file.
+   *
+   * @param aURI       URI to save to file. Some implementations of this interface
+   *                   may also support <CODE>nullptr</CODE> to imply the currently
+   *                   loaded URI.
+   * @param aTriggeringPrincipal
+   *                   The triggering principal for the URI we're saving.
+   * @param aCacheKey  The necko cache key integer.
+   * @param aReferrerInfo  The referrer info for compute and send referrer via
+   *                   HTTP Referer header.
+   * @param aCookieJarSettings The cookieJarSettings for the HTTP channel which
+   *                   is saving the URI.
+   * @param aPostData  Post data to pass with an HTTP request or
+   *                   <CODE>nullptr</CODE>.
+   * @param aExtraHeaders Additional headers to supply with an HTTP request
+   *                   or <CODE>nullptr</CODE>.
+   * @param aFile      Target file. This may be a nsIFile object or an
+   *                   nsIURI object with a file scheme or a scheme that
+   *                   supports uploading (e.g. ftp).
+   * @param aContentPolicyType The type of content we're saving.
+   * @param aPrivacyContext A context from which the privacy status of this
+   *                   save operation can be determined. Must only be null
+   *                   in situations in which no such context is available
+   *                   (eg. the operation has no logical association with any
+   *                   window or document)
+   *
+   * @see nsIFile
+   * @see nsIURI
+   * @see nsIInputStream
+   *
+   * @throws NS_ERROR_INVALID_ARG One or more arguments was invalid.
+   */
+  void saveURI(in nsIURI aURI, in nsIPrincipal aTriggeringPrincipal,
+      in unsigned long aCacheKey,
+      in nsIReferrerInfo aReferrerInfo,
+      in nsICookieJarSettings aCookieJarSettings,
+      in nsIInputStream aPostData,
+      in string aExtraHeaders, in nsISupports aFile,
+      in nsContentPolicyType aContentPolicyType,
+      in nsILoadContext aPrivacyContext);
+
+  /**
+   * @param aIsPrivate Treat the save operation as private (ie. with
+   *                   regards to networking operations and persistence
+   *                   of intermediate data, etc.)
+   * @see saveURI for all other parameter descriptions
+   */
+  void savePrivacyAwareURI(in nsIURI aURI,
+      in nsIPrincipal aTriggeringPrincipal, in unsigned long aCacheKey,
+      in nsIReferrerInfo aReferrerInfo,
+      in nsICookieJarSettings aCookieJarSettings,
+      in nsIInputStream aPostData,
+      in string aExtraHeaders, in nsISupports aFile,
+      in nsContentPolicyType aContentPolicyType,
+      in boolean aIsPrivate);
+
+  /**
+   * Save a channel to a file. It must not be opened yet.
+   * @see saveURI
+   */
+  void saveChannel(in nsIChannel aChannel, in nsISupports aFile);
+
+  /** Output only the current selection as opposed to the whole document. */
+  const unsigned long ENCODE_FLAGS_SELECTION_ONLY = 1;
+  /**
+   * For plaintext output. Convert html to plaintext that looks like the html.
+   * Implies wrap (except inside &lt;pre&gt;), since html wraps.
+   * HTML output: always do prettyprinting, ignoring existing formatting.
+   */
+  const unsigned long ENCODE_FLAGS_FORMATTED = 2;
+  /**
+   * Output without formatting or wrapping the content. This flag
+   * may be used to preserve the original formatting as much as possible.
+   */
+  const unsigned long ENCODE_FLAGS_RAW = 4;
+  /** Output only the body section, no HTML tags. */
+  const unsigned long ENCODE_FLAGS_BODY_ONLY = 8;
+  /** Wrap even if when not doing formatted output (e.g. for text fields). */
+  const unsigned long ENCODE_FLAGS_PREFORMATTED = 16;
+  /** Wrap documents at the specified column. */
+  const unsigned long ENCODE_FLAGS_WRAP = 32;
+  /**
+   * For plaintext output. Output for format flowed (RFC 2646). This is used
+   * when converting to text for mail sending. This differs just slightly
+   * but in an important way from normal formatted, and that is that
+   * lines are space stuffed. This can't (correctly) be done later.
+   */
+  const unsigned long ENCODE_FLAGS_FORMAT_FLOWED = 64;
+  /** Convert links to absolute links where possible. */
+  const unsigned long ENCODE_FLAGS_ABSOLUTE_LINKS = 128;
+
+  /**
+   * Output with carriage return line breaks. May also be combined with
+   * ENCODE_FLAGS_LF_LINEBREAKS and if neither is specified, the platform
+   * default format is used.
+   */
+  const unsigned long ENCODE_FLAGS_CR_LINEBREAKS = 512;
+  /**
+   * Output with linefeed line breaks. May also be combined with
+   * ENCODE_FLAGS_CR_LINEBREAKS and if neither is specified, the platform
+   * default format is used.
+   */
+  const unsigned long ENCODE_FLAGS_LF_LINEBREAKS = 1024;
+  /** For plaintext output. Output the content of noscript elements. */
+  const unsigned long ENCODE_FLAGS_NOSCRIPT_CONTENT = 2048;
+  /** For plaintext output. Output the content of noframes elements. */
+  const unsigned long ENCODE_FLAGS_NOFRAMES_CONTENT = 4096;
+
+  /**
+   * Encode basic entities, e.g. output &nbsp; instead of character code 0xa0.
+   * The basic set is just &nbsp; &amp; &lt; &gt; &quot; for interoperability
+   * with older products that don't support &alpha; and friends.
+   */
+  const unsigned long ENCODE_FLAGS_ENCODE_BASIC_ENTITIES = 8192;
+
+  /**
+   * Save the specified DOM document to file and optionally all linked files
+   * (e.g. images, CSS, JS & subframes). Do not call this method until the
+   * document has finished loading!
+   *
+   * @param aDocument          Document to save to file. Some implementations of
+   *                           this interface may also support <CODE>nullptr</CODE>
+   *                           to imply the currently loaded document.  Can be an
+   *                           nsIWebBrowserPersistDocument or Document.
+   * @param aFile              Target local file. This may be a nsIFile object or an
+   *                           nsIURI object with a file scheme or a scheme that
+   *                           supports uploading (e.g. ftp).
+   * @param aDataPath          Path to directory where URIs linked to the document
+   *                           are saved or nullptr if no linked URIs should be saved.
+   *                           This may be a nsIFile object or an nsIURI object
+   *                           with a file scheme.
+   * @param aOutputContentType The desired MIME type format to save the
+   *                           document and all subdocuments into or nullptr to use
+   *                           the default behaviour.
+   * @param aEncodingFlags     Flags to pass to the encoder.
+   * @param aWrapColumn        For text documents, indicates the desired width to
+   *                           wrap text at. Parameter is ignored if wrapping is not
+   *                           specified by the encoding flags.
+   *
+   * @see nsIWebBrowserPersistDocument
+   * @see WebBrowserPersistable
+   * @see nsIFile
+   * @see nsIURI
+   *
+   * @throws NS_ERROR_INVALID_ARG One or more arguments was invalid.
+   */
+  void saveDocument(in nsISupports aDocument,
+     in nsISupports aFile, in nsISupports aDataPath,
+     in string aOutputContentType, in unsigned long aEncodingFlags,
+     in unsigned long aWrapColumn);
+
+  /**
+   * Cancels the current operation. The caller is responsible for cleaning up
+   * partially written files or directories. This has the same effect as calling
+   * cancel with an argument of NS_BINDING_ABORTED.
+   */
+  void cancelSave();
+};
+
+/**
+ * We don't export nsWebBrowserPersist.h as a public header, so we need a place
+ * to put the CID/ContractID. All places uses the WebBrowserPersist include
+ * nsIWebBrowserPersist.h, so we define our contract IDs here for now.
+ */
+%{ C++
+// {7E677795-C582-4cd1-9E8D-8271B3474D2A}
+#define NS_WEBBROWSERPERSIST_CID \
+  { 0x7e677795, 0xc582, 0x4cd1, { 0x9e, 0x8d, 0x82, 0x71, 0xb3, 0x47, 0x4d, 0x2a } }
+#define NS_WEBBROWSERPERSIST_CONTRACTID \
+  "@mozilla.org/embedding/browser/nsWebBrowserPersist;1"
+%}
diff --git a/dom/webbrowserpersist/nsIWebBrowserPersistDocument.idl b/dom/webbrowserpersist/nsIWebBrowserPersistDocument.idl
new file mode 100644
index 0000000000..9f1f77fad5
--- /dev/null
+++ b/dom/webbrowserpersist/nsIWebBrowserPersistDocument.idl
@@ -0,0 +1,227 @@
+/* -*- Mode: IDL; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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"
+#include "nsIContentPolicy.idl"
+
+interface nsIInputStream;
+interface nsIOutputStream;
+interface nsIPrincipal;
+interface nsIRemoteTab;
+interface nsIWebBrowserPersistResourceVisitor;
+interface nsIWebBrowserPersistWriteCompletion;
+interface nsIReferrerInfo;
+interface nsISHEntry;
+interface nsICookieJarSettings;
+
+webidl BrowsingContext;
+
+native SHEntryRef(already_AddRefed<nsISHEntry>);
+
+/**
+ * Interface for the URI-mapping information that can be supplied when
+ * serializing the DOM of an nsIWebBrowserPersistDocument.
+ *
+ * @see nsIWebBrowserPersistDocument
+ */
+[scriptable, uuid(d52e8b93-2771-45e8-a5b0-6e12b667046b)]
+interface nsIWebBrowserPersistURIMap : nsISupports
+{
+  /**
+   * The number of URI mappings.
+   */
+  readonly attribute unsigned long numMappedURIs;
+
+  /**
+   * Obtain the URI mapping at the given index, which must be less than
+   * numMappedURIs, as a pair of URI spec strings.
+   */
+  void getURIMapping(in unsigned long aIndex,
+                     out AUTF8String aMapFrom,
+                     out AUTF8String aMapTo);
+
+  /**
+   * The spec of the base URI that the document will have after it is
+   * serialized.
+   */
+  readonly attribute AUTF8String targetBaseURI;
+};
+
+/**
+ * Interface representing a document that can be serialized with
+ * nsIWebBrowserPersist; it may or may not be in this process.  Some
+ * information is exposed as attributes, which may or may not reflect
+ * changes made to the underlying document; most of these are
+ * self-explanatory from their names and types.
+ */
+[scriptable, builtinclass, uuid(74aa4918-5d15-46b6-9ccf-74f9696d721d)]
+interface nsIWebBrowserPersistDocument : nsISupports
+{
+  readonly attribute boolean isClosed;
+  readonly attribute boolean isPrivate;
+  readonly attribute AUTF8String documentURI;
+  readonly attribute AUTF8String baseURI;
+  readonly attribute ACString contentType;
+  readonly attribute ACString characterSet;
+  readonly attribute AString title;
+  readonly attribute nsIReferrerInfo referrerInfo;
+  readonly attribute nsICookieJarSettings cookieJarSettings;
+  readonly attribute AString contentDisposition;
+  readonly attribute nsIInputStream postData;
+  readonly attribute nsIPrincipal principal;
+
+  /**
+   * The cache key.  Unlike in nsISHEntry, where it's wrapped in an
+   * nsISupportsPRUint32, this is just the integer.
+   */
+  [infallible]
+  readonly attribute unsigned long cacheKey;
+
+  /**
+   * This attribute is set by nsIWebBrowserPersist implementations to
+   * propagate persist flags that apply to the DOM traversal and
+   * serialization (rather than to managing file I/O).
+   */
+  attribute unsigned long persistFlags;
+
+  /**
+   * Walk the DOM searching for external resources needed to render it.
+   * The visitor callbacks may be called either before or after
+   * readResources returns.
+   *
+   * @see nsIWebBrowserPersistResourceVisitor
+   */
+  void readResources(in nsIWebBrowserPersistResourceVisitor aVisitor);
+
+  /**
+   * Serialize the document's DOM.
+   *
+   * @param aStream       The output stream to write the document to.
+   *
+   * @param aURIMap       Optional; specifies URI rewriting to perform on
+   *                      external references (as read by readResources).
+   *                      If given, also causes relative hyperlinks to be
+   *                      converted to absolute in the written text.
+   *
+   * @param aRequestedContentType
+   *                      The desired MIME type to save the document as;
+   *                      optional and defaults to the document's type.
+   *                      (If no encoder exists for that type, "text/html"
+   *                      is used instead.)
+   *
+   * @param aEncoderFlags Flags to pass to the encoder.
+   *
+   * @param aWrapColumn   Desired text width, ignored if wrapping is not
+   *                      specified by the encoding flags, or if 0.
+   *
+   * @param aCompletion   Callback invoked when writing is complete.
+   *                      It may be called either before or after writeContent
+   *                      returns.
+   *
+   * @see nsIDocumentEncoder
+   */
+  void writeContent(in nsIOutputStream aStream,
+                    in nsIWebBrowserPersistURIMap aURIMap,
+                    in ACString aRequestedContentType,
+                    in unsigned long aEncoderFlags,
+                    in unsigned long aWrapColumn,
+                    in nsIWebBrowserPersistWriteCompletion aCompletion);
+
+  [notxpcom, nostdcall] SHEntryRef GetHistory();
+};
+
+/**
+ * Asynchronous visitor that receives external resources linked by an
+ * nsIWebBrowserPersistDocument and which are needed to render the
+ * document.
+ */
+[scriptable, uuid(8ce37706-b7d3-481a-be68-54f174fc0d0a)]
+interface nsIWebBrowserPersistResourceVisitor : nsISupports
+{
+  /**
+   * Indicates a resource that is not a document; e.g., an image, script,
+   * or stylesheet.
+   *
+   * @param aDocument   The document containing the reference.
+   * @param aURI        The absolute URI spec for the referenced resource.
+   * @param aContentPolicyType The type of resource.
+   */
+  void visitResource(in nsIWebBrowserPersistDocument aDocument,
+                     in AUTF8String aURI,
+                     in nsContentPolicyType aContentPolicyType);
+
+  /**
+   * Indicates a subdocument resource; e.g., a frame or iframe.
+   *
+   * @param aDocument     The document containing the reference.
+   * @param aSubDocument  The referenced document.
+   */
+  void visitDocument(in nsIWebBrowserPersistDocument aDocument,
+                     in nsIWebBrowserPersistDocument aSubDocument);
+
+  /**
+   * Indicates a cross origin subdocument resource; e.g., a frame
+   * or iframe loaded in another process.
+   *
+   * @param aDocument     The document containing the reference.
+   * @param aContext      The referenced document's browsing context.
+   */
+  void visitBrowsingContext(in nsIWebBrowserPersistDocument aDocument,
+                            in BrowsingContext aContext);
+
+  /**
+   * Indicates that the document traversal is complete.
+   *
+   * @param aDocument   The document that was being traversed.
+   * @param aStatus     Indicates whether the traversal encountered an error.
+   */
+  void endVisit(in nsIWebBrowserPersistDocument aDocument,
+                in nsresult aStatus);
+};
+
+/**
+ * Asynchronous callback for when nsIWebBrowserPersistDocument is finished
+ * serializing the document's DOM.
+ */
+[scriptable, function, uuid(a07e6892-38ae-4207-8340-7fa6ec446ed6)]
+interface nsIWebBrowserPersistWriteCompletion : nsISupports
+{
+  /**
+   * Indicates that serialization is finished.
+   *
+   * @param aDocument     The document that was being serialized.
+   *
+   * @param aStream       The stream that was being written to.  If it
+   *                      needs to be closed, the callback must do that;
+   *                      the serialization process leaves it open.
+   *
+   * @param aContentType  The content type with which the document was
+   *                      actually serialized; this may be useful to set
+   *                      metadata on the result, or if uploading it.
+   *
+   * @param aStatus       Indicates whether serialization encountered an error.
+   */
+  void onFinish(in nsIWebBrowserPersistDocument aDocument,
+                in nsIOutputStream aStream,
+                in ACString aContentType,
+                in nsresult aStatus);
+};
+
+/**
+ * Asynchronous callback for creating a persistable document from some
+ * other object.
+ *
+ * XXXbz This should really be changed to just return a promise that
+ * then gets resolved or rejected...
+ *
+ * @see WebBrowserPersistable in FrameLoader.webidl.
+ */
+[scriptable, uuid(321e3174-594f-4036-b7be-791b821bd376)]
+interface nsIWebBrowserPersistDocumentReceiver : nsISupports
+{
+  void onDocumentReady(in nsIWebBrowserPersistDocument aDocument);
+  void onError(in nsresult aFailure);
+};
diff --git a/dom/webbrowserpersist/nsWebBrowserPersist.cpp b/dom/webbrowserpersist/nsWebBrowserPersist.cpp
new file mode 100644
index 0000000000..eac9681f2c
--- /dev/null
+++ b/dom/webbrowserpersist/nsWebBrowserPersist.cpp
@@ -0,0 +1,2728 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * 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/ArrayUtils.h"
+#include "mozilla/TextUtils.h"
+
+#include "nspr.h"
+
+#include "nsIFileStreams.h"  // New Necko file streams
+#include <algorithm>
+
+#include "nsNetCID.h"
+#include "nsNetUtil.h"
+#include "nsIClassOfService.h"
+#include "nsIInterfaceRequestorUtils.h"
+#include "nsILoadContext.h"
+#include "nsIPrivateBrowsingChannel.h"
+#include "nsComponentManagerUtils.h"
+#include "nsIStorageStream.h"
+#include "nsISeekableStream.h"
+#include "nsIHttpChannel.h"
+#include "nsIEncodedChannel.h"
+#include "nsIUploadChannel.h"
+#include "nsICacheInfoChannel.h"
+#include "nsIFileChannel.h"
+#include "nsEscape.h"
+#include "nsUnicharUtils.h"
+#include "nsIStringEnumerator.h"
+#include "nsContentCID.h"
+#include "nsStreamUtils.h"
+
+#include "nsCExternalHandlerService.h"
+
+#include "nsIURL.h"
+#include "nsIFileURL.h"
+#include "nsIWebProgressListener.h"
+#include "nsIAuthPrompt.h"
+#include "nsIPrompt.h"
+#include "nsIFormControl.h"
+#include "nsIThreadRetargetableRequest.h"
+#include "nsContentUtils.h"
+
+#include "nsIStringBundle.h"
+#include "nsIProtocolHandler.h"
+
+#include "nsWebBrowserPersist.h"
+#include "WebBrowserPersistLocalDocument.h"
+
+#include "nsIContent.h"
+#include "nsIMIMEInfo.h"
+#include "mozilla/dom/HTMLInputElement.h"
+#include "mozilla/dom/HTMLSharedElement.h"
+#include "mozilla/net/CookieJarSettings.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/Printf.h"
+#include "ReferrerInfo.h"
+#include "nsIURIMutator.h"
+#include "mozilla/WebBrowserPersistDocumentParent.h"
+#include "mozilla/dom/CanonicalBrowsingContext.h"
+#include "mozilla/dom/WindowGlobalParent.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/dom/PContentParent.h"
+#include "mozilla/dom/BrowserParent.h"
+#include "nsIDocumentEncoder.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+// Buffer file writes in 32kb chunks
+#define BUFFERED_OUTPUT_SIZE (1024 * 32)
+
+struct nsWebBrowserPersist::WalkData {
+  nsCOMPtr<nsIWebBrowserPersistDocument> mDocument;
+  nsCOMPtr<nsIURI> mFile;
+  nsCOMPtr<nsIURI> mDataPath;
+};
+
+// Information about a DOM document
+struct nsWebBrowserPersist::DocData {
+  nsCOMPtr<nsIURI> mBaseURI;
+  nsCOMPtr<nsIWebBrowserPersistDocument> mDocument;
+  nsCOMPtr<nsIURI> mFile;
+  nsCString mCharset;
+};
+
+// Information about a URI
+struct nsWebBrowserPersist::URIData {
+  bool mNeedsPersisting;
+  bool mSaved;
+  bool mIsSubFrame;
+  bool mDataPathIsRelative;
+  bool mNeedsFixup;
+  nsString mFilename;
+  nsString mSubFrameExt;
+  nsCOMPtr<nsIURI> mFile;
+  nsCOMPtr<nsIURI> mDataPath;
+  nsCOMPtr<nsIURI> mRelativeDocumentURI;
+  nsCOMPtr<nsIPrincipal> mTriggeringPrincipal;
+  nsCOMPtr<nsICookieJarSettings> mCookieJarSettings;
+  nsContentPolicyType mContentPolicyType;
+  nsCString mRelativePathToData;
+  nsCString mCharset;
+
+  nsresult GetLocalURI(nsIURI* targetBaseURI, nsCString& aSpecOut);
+};
+
+// Information about the output stream
+// Note that this data structure (and the map that nsWebBrowserPersist keeps,
+// where these are values) is used from two threads: the main thread,
+// and the background task thread.
+// The background thread only writes to mStream (from OnDataAvailable), and
+// this access is guarded using mStreamMutex. It reads the mFile member, which
+// is only written to on the main thread when the object is constructed and
+// from OnStartRequest (if mCalcFileExt), both guaranteed to happen before
+// OnDataAvailable is fired.
+// The main thread gets OnStartRequest, OnStopRequest, and progress sink events,
+// and accesses the other members.
+struct nsWebBrowserPersist::OutputData {
+  nsCOMPtr<nsIURI> mFile;
+  nsCOMPtr<nsIURI> mOriginalLocation;
+  nsCOMPtr<nsIOutputStream> mStream;
+  Mutex mStreamMutex MOZ_UNANNOTATED;
+  int64_t mSelfProgress;
+  int64_t mSelfProgressMax;
+  bool mCalcFileExt;
+
+  OutputData(nsIURI* aFile, nsIURI* aOriginalLocation, bool aCalcFileExt)
+      : mFile(aFile),
+        mOriginalLocation(aOriginalLocation),
+        mStreamMutex("nsWebBrowserPersist::OutputData::mStreamMutex"),
+        mSelfProgress(0),
+        mSelfProgressMax(10000),
+        mCalcFileExt(aCalcFileExt) {}
+  ~OutputData() {
+    // Gaining this lock in the destructor is pretty icky. It should be OK
+    // because the only other place we lock the mutex is in OnDataAvailable,
+    // which will never itself cause the OutputData instance to be
+    // destroyed.
+    MutexAutoLock lock(mStreamMutex);
+    if (mStream) {
+      mStream->Close();
+    }
+  }
+};
+
+struct nsWebBrowserPersist::UploadData {
+  nsCOMPtr<nsIURI> mFile;
+  int64_t mSelfProgress;
+  int64_t mSelfProgressMax;
+
+  explicit UploadData(nsIURI* aFile)
+      : mFile(aFile), mSelfProgress(0), mSelfProgressMax(10000) {}
+};
+
+struct nsWebBrowserPersist::CleanupData {
+  nsCOMPtr<nsIFile> mFile;
+  // Snapshot of what the file actually is at the time of creation so that if
+  // it transmutes into something else later on it can be ignored. For example,
+  // catch files that turn into dirs or vice versa.
+  bool mIsDirectory;
+};
+
+class nsWebBrowserPersist::OnWalk final
+    : public nsIWebBrowserPersistResourceVisitor {
+ public:
+  OnWalk(nsWebBrowserPersist* aParent, nsIURI* aFile, nsIFile* aDataPath)
+      : mParent(aParent),
+        mFile(aFile),
+        mDataPath(aDataPath),
+        mPendingDocuments(1),
+        mStatus(NS_OK) {}
+
+  NS_DECL_NSIWEBBROWSERPERSISTRESOURCEVISITOR
+  NS_DECL_ISUPPORTS
+ private:
+  RefPtr<nsWebBrowserPersist> mParent;
+  nsCOMPtr<nsIURI> mFile;
+  nsCOMPtr<nsIFile> mDataPath;
+
+  uint32_t mPendingDocuments;
+  nsresult mStatus;
+
+  virtual ~OnWalk() = default;
+};
+
+NS_IMPL_ISUPPORTS(nsWebBrowserPersist::OnWalk,
+                  nsIWebBrowserPersistResourceVisitor)
+
+class nsWebBrowserPersist::OnRemoteWalk final
+    : public nsIWebBrowserPersistDocumentReceiver {
+ public:
+  OnRemoteWalk(nsIWebBrowserPersistResourceVisitor* aVisitor,
+               nsIWebBrowserPersistDocument* aDocument)
+      : mVisitor(aVisitor), mDocument(aDocument) {}
+
+  NS_DECL_NSIWEBBROWSERPERSISTDOCUMENTRECEIVER
+  NS_DECL_ISUPPORTS
+ private:
+  nsCOMPtr<nsIWebBrowserPersistResourceVisitor> mVisitor;
+  nsCOMPtr<nsIWebBrowserPersistDocument> mDocument;
+
+  virtual ~OnRemoteWalk() = default;
+};
+
+NS_IMPL_ISUPPORTS(nsWebBrowserPersist::OnRemoteWalk,
+                  nsIWebBrowserPersistDocumentReceiver)
+
+class nsWebBrowserPersist::OnWrite final
+    : public nsIWebBrowserPersistWriteCompletion {
+ public:
+  OnWrite(nsWebBrowserPersist* aParent, nsIURI* aFile, nsIFile* aLocalFile)
+      : mParent(aParent), mFile(aFile), mLocalFile(aLocalFile) {}
+
+  NS_DECL_NSIWEBBROWSERPERSISTWRITECOMPLETION
+  NS_DECL_ISUPPORTS
+ private:
+  RefPtr<nsWebBrowserPersist> mParent;
+  nsCOMPtr<nsIURI> mFile;
+  nsCOMPtr<nsIFile> mLocalFile;
+
+  virtual ~OnWrite() = default;
+};
+
+NS_IMPL_ISUPPORTS(nsWebBrowserPersist::OnWrite,
+                  nsIWebBrowserPersistWriteCompletion)
+
+class nsWebBrowserPersist::FlatURIMap final
+    : public nsIWebBrowserPersistURIMap {
+ public:
+  explicit FlatURIMap(const nsACString& aTargetBase)
+      : mTargetBase(aTargetBase) {}
+
+  void Add(const nsACString& aMapFrom, const nsACString& aMapTo) {
+    mMapFrom.AppendElement(aMapFrom);
+    mMapTo.AppendElement(aMapTo);
+  }
+
+  NS_DECL_NSIWEBBROWSERPERSISTURIMAP
+  NS_DECL_ISUPPORTS
+
+ private:
+  nsTArray<nsCString> mMapFrom;
+  nsTArray<nsCString> mMapTo;
+  nsCString mTargetBase;
+
+  virtual ~FlatURIMap() = default;
+};
+
+NS_IMPL_ISUPPORTS(nsWebBrowserPersist::FlatURIMap, nsIWebBrowserPersistURIMap)
+
+NS_IMETHODIMP
+nsWebBrowserPersist::FlatURIMap::GetNumMappedURIs(uint32_t* aNum) {
+  MOZ_ASSERT(mMapFrom.Length() == mMapTo.Length());
+  *aNum = mMapTo.Length();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsWebBrowserPersist::FlatURIMap::GetTargetBaseURI(nsACString& aTargetBase) {
+  aTargetBase = mTargetBase;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsWebBrowserPersist::FlatURIMap::GetURIMapping(uint32_t aIndex,
+                                               nsACString& aMapFrom,
+                                               nsACString& aMapTo) {
+  MOZ_ASSERT(mMapFrom.Length() == mMapTo.Length());
+  if (aIndex >= mMapTo.Length()) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  aMapFrom = mMapFrom[aIndex];
+  aMapTo = mMapTo[aIndex];
+  return NS_OK;
+}
+
+// Maximum file length constant. The max file name length is
+// volume / server dependent but it is difficult to obtain
+// that information. Instead this constant is a reasonable value that
+// modern systems should able to cope with.
+const uint32_t kDefaultMaxFilenameLength = 64;
+
+// Default flags for persistence
+const uint32_t kDefaultPersistFlags =
+    nsIWebBrowserPersist::PERSIST_FLAGS_NO_CONVERSION |
+    nsIWebBrowserPersist::PERSIST_FLAGS_REPLACE_EXISTING_FILES;
+
+// String bundle where error messages come from
+const char* kWebBrowserPersistStringBundle =
+    "chrome://global/locale/nsWebBrowserPersist.properties";
+
+nsWebBrowserPersist::nsWebBrowserPersist()
+    : mCurrentDataPathIsRelative(false),
+      mCurrentThingsToPersist(0),
+      mOutputMapMutex("nsWebBrowserPersist::mOutputMapMutex"),
+      mFirstAndOnlyUse(true),
+      mSavingDocument(false),
+      mCancel(false),
+      mEndCalled(false),
+      mCompleted(false),
+      mStartSaving(false),
+      mReplaceExisting(true),
+      mSerializingOutput(false),
+      mIsPrivate(false),
+      mPersistFlags(kDefaultPersistFlags),
+      mPersistResult(NS_OK),
+      mTotalCurrentProgress(0),
+      mTotalMaxProgress(0),
+      mWrapColumn(72),
+      mEncodingFlags(0) {}
+
+nsWebBrowserPersist::~nsWebBrowserPersist() { Cleanup(); }
+
+//*****************************************************************************
+// nsWebBrowserPersist::nsISupports
+//*****************************************************************************
+
+NS_IMPL_ADDREF(nsWebBrowserPersist)
+NS_IMPL_RELEASE(nsWebBrowserPersist)
+
+NS_INTERFACE_MAP_BEGIN(nsWebBrowserPersist)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIWebBrowserPersist)
+  NS_INTERFACE_MAP_ENTRY(nsIWebBrowserPersist)
+  NS_INTERFACE_MAP_ENTRY(nsICancelable)
+  NS_INTERFACE_MAP_ENTRY(nsIInterfaceRequestor)
+  NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
+  NS_INTERFACE_MAP_ENTRY(nsIStreamListener)
+  NS_INTERFACE_MAP_ENTRY(nsIThreadRetargetableStreamListener)
+  NS_INTERFACE_MAP_ENTRY(nsIRequestObserver)
+  NS_INTERFACE_MAP_ENTRY(nsIProgressEventSink)
+NS_INTERFACE_MAP_END
+
+//*****************************************************************************
+// nsWebBrowserPersist::nsIInterfaceRequestor
+//*****************************************************************************
+
+NS_IMETHODIMP nsWebBrowserPersist::GetInterface(const nsIID& aIID,
+                                                void** aIFace) {
+  NS_ENSURE_ARG_POINTER(aIFace);
+
+  *aIFace = nullptr;
+
+  nsresult rv = QueryInterface(aIID, aIFace);
+  if (NS_SUCCEEDED(rv)) {
+    return rv;
+  }
+
+  if (mProgressListener && (aIID.Equals(NS_GET_IID(nsIAuthPrompt)) ||
+                            aIID.Equals(NS_GET_IID(nsIPrompt)))) {
+    mProgressListener->QueryInterface(aIID, aIFace);
+    if (*aIFace) return NS_OK;
+  }
+
+  nsCOMPtr<nsIInterfaceRequestor> req = do_QueryInterface(mProgressListener);
+  if (req) {
+    return req->GetInterface(aIID, aIFace);
+  }
+
+  return NS_ERROR_NO_INTERFACE;
+}
+
+//*****************************************************************************
+// nsWebBrowserPersist::nsIWebBrowserPersist
+//*****************************************************************************
+
+NS_IMETHODIMP nsWebBrowserPersist::GetPersistFlags(uint32_t* aPersistFlags) {
+  NS_ENSURE_ARG_POINTER(aPersistFlags);
+  *aPersistFlags = mPersistFlags;
+  return NS_OK;
+}
+NS_IMETHODIMP nsWebBrowserPersist::SetPersistFlags(uint32_t aPersistFlags) {
+  mPersistFlags = aPersistFlags;
+  mReplaceExisting = (mPersistFlags & PERSIST_FLAGS_REPLACE_EXISTING_FILES);
+  mSerializingOutput = (mPersistFlags & PERSIST_FLAGS_SERIALIZE_OUTPUT);
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsWebBrowserPersist::GetCurrentState(uint32_t* aCurrentState) {
+  NS_ENSURE_ARG_POINTER(aCurrentState);
+  if (mCompleted) {
+    *aCurrentState = PERSIST_STATE_FINISHED;
+  } else if (mFirstAndOnlyUse) {
+    *aCurrentState = PERSIST_STATE_SAVING;
+  } else {
+    *aCurrentState = PERSIST_STATE_READY;
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsWebBrowserPersist::GetResult(nsresult* aResult) {
+  NS_ENSURE_ARG_POINTER(aResult);
+  *aResult = mPersistResult;
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsWebBrowserPersist::GetProgressListener(
+    nsIWebProgressListener** aProgressListener) {
+  NS_ENSURE_ARG_POINTER(aProgressListener);
+  *aProgressListener = mProgressListener;
+  NS_IF_ADDREF(*aProgressListener);
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsWebBrowserPersist::SetProgressListener(
+    nsIWebProgressListener* aProgressListener) {
+  mProgressListener = aProgressListener;
+  mProgressListener2 = do_QueryInterface(aProgressListener);
+  mEventSink = do_GetInterface(aProgressListener);
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsWebBrowserPersist::SaveURI(
+    nsIURI* aURI, nsIPrincipal* aPrincipal, uint32_t aCacheKey,
+    nsIReferrerInfo* aReferrerInfo, nsICookieJarSettings* aCookieJarSettings,
+    nsIInputStream* aPostData, const char* aExtraHeaders, nsISupports* aFile,
+    nsContentPolicyType aContentPolicyType, nsILoadContext* aPrivacyContext) {
+  bool isPrivate = aPrivacyContext && aPrivacyContext->UsePrivateBrowsing();
+  return SavePrivacyAwareURI(aURI, aPrincipal, aCacheKey, aReferrerInfo,
+                             aCookieJarSettings, aPostData, aExtraHeaders,
+                             aFile, aContentPolicyType, isPrivate);
+}
+
+NS_IMETHODIMP nsWebBrowserPersist::SavePrivacyAwareURI(
+    nsIURI* aURI, nsIPrincipal* aPrincipal, uint32_t aCacheKey,
+    nsIReferrerInfo* aReferrerInfo, nsICookieJarSettings* aCookieJarSettings,
+    nsIInputStream* aPostData, const char* aExtraHeaders, nsISupports* aFile,
+    nsContentPolicyType aContentPolicy, bool aIsPrivate) {
+  NS_ENSURE_TRUE(mFirstAndOnlyUse, NS_ERROR_FAILURE);
+  mFirstAndOnlyUse = false;  // Stop people from reusing this object!
+
+  nsCOMPtr<nsIURI> fileAsURI;
+  nsresult rv;
+  rv = GetValidURIFromObject(aFile, getter_AddRefs(fileAsURI));
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_INVALID_ARG);
+
+  // SaveURI doesn't like broken uris.
+  mPersistFlags |= PERSIST_FLAGS_FAIL_ON_BROKEN_LINKS;
+  rv = SaveURIInternal(aURI, aPrincipal, aContentPolicy, aCacheKey,
+                       aReferrerInfo, aCookieJarSettings, aPostData,
+                       aExtraHeaders, fileAsURI, false, aIsPrivate);
+  return NS_FAILED(rv) ? rv : NS_OK;
+}
+
+NS_IMETHODIMP nsWebBrowserPersist::SaveChannel(nsIChannel* aChannel,
+                                               nsISupports* aFile) {
+  NS_ENSURE_TRUE(mFirstAndOnlyUse, NS_ERROR_FAILURE);
+  mFirstAndOnlyUse = false;  // Stop people from reusing this object!
+
+  nsCOMPtr<nsIURI> fileAsURI;
+  nsresult rv;
+  rv = GetValidURIFromObject(aFile, getter_AddRefs(fileAsURI));
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_INVALID_ARG);
+
+  rv = aChannel->GetURI(getter_AddRefs(mURI));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // SaveURI doesn't like broken uris.
+  mPersistFlags |= PERSIST_FLAGS_FAIL_ON_BROKEN_LINKS;
+  rv = SaveChannelInternal(aChannel, fileAsURI, false);
+  return NS_FAILED(rv) ? rv : NS_OK;
+}
+
+NS_IMETHODIMP nsWebBrowserPersist::SaveDocument(nsISupports* aDocument,
+                                                nsISupports* aFile,
+                                                nsISupports* aDataPath,
+                                                const char* aOutputContentType,
+                                                uint32_t aEncodingFlags,
+                                                uint32_t aWrapColumn) {
+  NS_ENSURE_TRUE(mFirstAndOnlyUse, NS_ERROR_FAILURE);
+  mFirstAndOnlyUse = false;  // Stop people from reusing this object!
+
+  // We need a STATE_IS_NETWORK start/stop pair to bracket the
+  // notification callbacks.  For a whole document we generate those
+  // here and in EndDownload(), but for the single-request methods
+  // that's done in On{Start,Stop}Request instead.
+  mSavingDocument = true;
+
+  NS_ENSURE_ARG_POINTER(aDocument);
+  NS_ENSURE_ARG_POINTER(aFile);
+
+  nsCOMPtr<nsIURI> fileAsURI;
+  nsCOMPtr<nsIURI> datapathAsURI;
+  nsresult rv;
+
+  rv = GetValidURIFromObject(aFile, getter_AddRefs(fileAsURI));
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_INVALID_ARG);
+  if (aDataPath) {
+    rv = GetValidURIFromObject(aDataPath, getter_AddRefs(datapathAsURI));
+    NS_ENSURE_SUCCESS(rv, NS_ERROR_INVALID_ARG);
+  }
+
+  mWrapColumn = aWrapColumn;
+  mEncodingFlags = aEncodingFlags;
+
+  if (aOutputContentType) {
+    mContentType.AssignASCII(aOutputContentType);
+  }
+
+  // State start notification
+  if (mProgressListener) {
+    mProgressListener->OnStateChange(
+        nullptr, nullptr,
+        nsIWebProgressListener::STATE_START |
+            nsIWebProgressListener::STATE_IS_NETWORK,
+        NS_OK);
+  }
+
+  nsCOMPtr<nsIWebBrowserPersistDocument> doc = do_QueryInterface(aDocument);
+  if (!doc) {
+    nsCOMPtr<Document> localDoc = do_QueryInterface(aDocument);
+    if (localDoc) {
+      doc = new mozilla::WebBrowserPersistLocalDocument(localDoc);
+    } else {
+      rv = NS_ERROR_NO_INTERFACE;
+    }
+  }
+
+  bool closed = false;
+  if (doc && NS_SUCCEEDED(doc->GetIsClosed(&closed)) && !closed) {
+    rv = SaveDocumentInternal(doc, fileAsURI, datapathAsURI);
+  }
+
+  if (NS_FAILED(rv) || closed) {
+    SendErrorStatusChange(true, rv, nullptr, mURI);
+    EndDownload(rv);
+  }
+  return rv;
+}
+
+NS_IMETHODIMP nsWebBrowserPersist::Cancel(nsresult aReason) {
+  // No point cancelling if we're already complete.
+  if (mEndCalled) {
+    return NS_OK;
+  }
+  mCancel = true;
+  EndDownload(aReason);
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsWebBrowserPersist::CancelSave() {
+  return Cancel(NS_BINDING_ABORTED);
+}
+
+nsresult nsWebBrowserPersist::StartUpload(nsIStorageStream* storStream,
+                                          nsIURI* aDestinationURI,
+                                          const nsACString& aContentType) {
+  // setup the upload channel if the destination is not local
+  nsCOMPtr<nsIInputStream> inputstream;
+  nsresult rv = storStream->NewInputStream(0, getter_AddRefs(inputstream));
+  NS_ENSURE_TRUE(inputstream, NS_ERROR_FAILURE);
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+  return StartUpload(inputstream, aDestinationURI, aContentType);
+}
+
+nsresult nsWebBrowserPersist::StartUpload(nsIInputStream* aInputStream,
+                                          nsIURI* aDestinationURI,
+                                          const nsACString& aContentType) {
+  nsCOMPtr<nsIChannel> destChannel;
+  CreateChannelFromURI(aDestinationURI, getter_AddRefs(destChannel));
+  nsCOMPtr<nsIUploadChannel> uploadChannel(do_QueryInterface(destChannel));
+  NS_ENSURE_TRUE(uploadChannel, NS_ERROR_FAILURE);
+
+  // Set the upload stream
+  // NOTE: ALL data must be available in "inputstream"
+  nsresult rv = uploadChannel->SetUploadStream(aInputStream, aContentType, -1);
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+  rv = destChannel->AsyncOpen(this);
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+
+  // add this to the upload list
+  nsCOMPtr<nsISupports> keyPtr = do_QueryInterface(destChannel);
+  mUploadList.InsertOrUpdate(keyPtr, MakeUnique<UploadData>(aDestinationURI));
+
+  return NS_OK;
+}
+
+void nsWebBrowserPersist::SerializeNextFile() {
+  nsresult rv = NS_OK;
+  MOZ_ASSERT(mWalkStack.Length() == 0);
+
+  // First, handle gathered URIs.
+  // This is potentially O(n^2), when taking into account the
+  // number of times this method is called.  If it becomes a
+  // bottleneck, the count of not-yet-persisted URIs could be
+  // maintained separately, and we can skip iterating mURIMap if there are none.
+
+  // Persist each file in the uri map. The document(s)
+  // will be saved after the last one of these is saved.
+  for (const auto& entry : mURIMap) {
+    URIData* data = entry.GetWeak();
+
+    if (!data->mNeedsPersisting || data->mSaved) {
+      continue;
+    }
+
+    // Create a URI from the key.
+    nsCOMPtr<nsIURI> uri;
+    rv = NS_NewURI(getter_AddRefs(uri), entry.GetKey(), data->mCharset.get());
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      break;
+    }
+
+    // Make a URI to save the data to.
+    nsCOMPtr<nsIURI> fileAsURI = data->mDataPath;
+    rv = AppendPathToURI(fileAsURI, data->mFilename, fileAsURI);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      break;
+    }
+
+    rv = SaveURIInternal(uri, data->mTriggeringPrincipal,
+                         data->mContentPolicyType, 0, nullptr,
+                         data->mCookieJarSettings, nullptr, nullptr, fileAsURI,
+                         true, mIsPrivate);
+    // If SaveURIInternal fails, then it will have called EndDownload,
+    // which means that |data| is no longer valid memory. We MUST bail.
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      break;
+    }
+
+    if (rv == NS_OK) {
+      // URIData.mFile will be updated to point to the correct
+      // URI object when it is fixed up with the right file extension
+      // in OnStartRequest
+      data->mFile = fileAsURI;
+      data->mSaved = true;
+    } else {
+      data->mNeedsFixup = false;
+    }
+
+    if (mSerializingOutput) {
+      break;
+    }
+  }
+
+  // If there are downloads happening, wait until they're done; the
+  // OnStopRequest handler will call this method again.
+  if (mOutputMap.Count() > 0) {
+    return;
+  }
+
+  // If serializing, also wait until last upload is done.
+  if (mSerializingOutput && mUploadList.Count() > 0) {
+    return;
+  }
+
+  // If there are also no more documents, then we're done.
+  if (mDocList.Length() == 0) {
+    // ...or not quite done, if there are still uploads.
+    if (mUploadList.Count() > 0) {
+      return;
+    }
+    // Finish and clean things up.  Defer this because the caller
+    // may have been expecting to use the listeners that that
+    // method will clear.
+    NS_DispatchToCurrentThread(
+        NewRunnableMethod("nsWebBrowserPersist::FinishDownload", this,
+                          &nsWebBrowserPersist::FinishDownload));
+    return;
+  }
+
+  // There are no URIs to save, so just save the next document.
+  mStartSaving = true;
+  mozilla::UniquePtr<DocData> docData(mDocList.ElementAt(0));
+  mDocList.RemoveElementAt(0);  // O(n^2) but probably doesn't matter.
+  MOZ_ASSERT(docData);
+  if (!docData) {
+    EndDownload(NS_ERROR_FAILURE);
+    return;
+  }
+
+  mCurrentBaseURI = docData->mBaseURI;
+  mCurrentCharset = docData->mCharset;
+  mTargetBaseURI = docData->mFile;
+
+  // Save the document, fixing it up with the new URIs as we do
+
+  nsAutoCString targetBaseSpec;
+  if (mTargetBaseURI) {
+    rv = mTargetBaseURI->GetSpec(targetBaseSpec);
+    if (NS_FAILED(rv)) {
+      SendErrorStatusChange(true, rv, nullptr, nullptr);
+      EndDownload(rv);
+      return;
+    }
+  }
+
+  // mFlatURIMap must be rebuilt each time through SerializeNextFile, as
+  // mTargetBaseURI is used to create the relative URLs and will be different
+  // with each serialized document.
+  RefPtr<FlatURIMap> flatMap = new FlatURIMap(targetBaseSpec);
+  for (const auto& uriEntry : mURIMap) {
+    nsAutoCString mapTo;
+    nsresult rv = uriEntry.GetWeak()->GetLocalURI(mTargetBaseURI, mapTo);
+    if (NS_SUCCEEDED(rv) || !mapTo.IsVoid()) {
+      flatMap->Add(uriEntry.GetKey(), mapTo);
+    }
+  }
+  mFlatURIMap = std::move(flatMap);
+
+  nsCOMPtr<nsIFile> localFile;
+  GetLocalFileFromURI(docData->mFile, getter_AddRefs(localFile));
+  if (localFile) {
+    // if we're not replacing an existing file but the file
+    // exists, something is wrong
+    bool fileExists = false;
+    rv = localFile->Exists(&fileExists);
+    if (NS_SUCCEEDED(rv) && !mReplaceExisting && fileExists) {
+      rv = NS_ERROR_FILE_ALREADY_EXISTS;
+    }
+    if (NS_FAILED(rv)) {
+      SendErrorStatusChange(false, rv, nullptr, docData->mFile);
+      EndDownload(rv);
+      return;
+    }
+  }
+  nsCOMPtr<nsIOutputStream> outputStream;
+  rv = MakeOutputStream(docData->mFile, getter_AddRefs(outputStream));
+  if (NS_SUCCEEDED(rv) && !outputStream) {
+    rv = NS_ERROR_FAILURE;
+  }
+  if (NS_FAILED(rv)) {
+    SendErrorStatusChange(false, rv, nullptr, docData->mFile);
+    EndDownload(rv);
+    return;
+  }
+
+  RefPtr<OnWrite> finish = new OnWrite(this, docData->mFile, localFile);
+  rv = docData->mDocument->WriteContent(outputStream, mFlatURIMap,
+                                        NS_ConvertUTF16toUTF8(mContentType),
+                                        mEncodingFlags, mWrapColumn, finish);
+  if (NS_FAILED(rv)) {
+    SendErrorStatusChange(false, rv, nullptr, docData->mFile);
+    EndDownload(rv);
+  }
+}
+
+NS_IMETHODIMP
+nsWebBrowserPersist::OnWrite::OnFinish(nsIWebBrowserPersistDocument* aDoc,
+                                       nsIOutputStream* aStream,
+                                       const nsACString& aContentType,
+                                       nsresult aStatus) {
+  nsresult rv = aStatus;
+
+  if (NS_FAILED(rv)) {
+    mParent->SendErrorStatusChange(false, rv, nullptr, mFile);
+    mParent->EndDownload(rv);
+    return NS_OK;
+  }
+  if (!mLocalFile) {
+    nsCOMPtr<nsIStorageStream> storStream(do_QueryInterface(aStream));
+    if (storStream) {
+      aStream->Close();
+      rv = mParent->StartUpload(storStream, mFile, aContentType);
+      if (NS_FAILED(rv)) {
+        mParent->SendErrorStatusChange(false, rv, nullptr, mFile);
+        mParent->EndDownload(rv);
+      }
+      // Either we failed and we're done, or we're uploading and
+      // the OnStopRequest callback is responsible for the next
+      // SerializeNextFile().
+      return NS_OK;
+    }
+  }
+  NS_DispatchToCurrentThread(
+      NewRunnableMethod("nsWebBrowserPersist::SerializeNextFile", mParent,
+                        &nsWebBrowserPersist::SerializeNextFile));
+  return NS_OK;
+}
+
+//*****************************************************************************
+// nsWebBrowserPersist::nsIRequestObserver
+//*****************************************************************************
+
+NS_IMETHODIMP nsWebBrowserPersist::OnStartRequest(nsIRequest* request) {
+  if (mProgressListener) {
+    uint32_t stateFlags = nsIWebProgressListener::STATE_START |
+                          nsIWebProgressListener::STATE_IS_REQUEST;
+    if (!mSavingDocument) {
+      stateFlags |= nsIWebProgressListener::STATE_IS_NETWORK;
+    }
+    mProgressListener->OnStateChange(nullptr, request, stateFlags, NS_OK);
+  }
+
+  nsCOMPtr<nsIChannel> channel = do_QueryInterface(request);
+  NS_ENSURE_TRUE(channel, NS_ERROR_FAILURE);
+
+  nsCOMPtr<nsISupports> keyPtr = do_QueryInterface(request);
+  OutputData* data = mOutputMap.Get(keyPtr);
+
+  // NOTE: This code uses the channel as a hash key so it will not
+  //       recognize redirected channels because the key is not the same.
+  //       When that happens we remove and add the data entry to use the
+  //       new channel as the hash key.
+  if (!data) {
+    UploadData* upData = mUploadList.Get(keyPtr);
+    if (!upData) {
+      // Redirect? Try and fixup the output table
+      nsresult rv = FixRedirectedChannelEntry(channel);
+      NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+
+      // Should be able to find the data after fixup unless redirects
+      // are disabled.
+      data = mOutputMap.Get(keyPtr);
+      if (!data) {
+        return NS_ERROR_FAILURE;
+      }
+    }
+  }
+
+  if (data && data->mFile) {
+    nsCOMPtr<nsIThreadRetargetableRequest> r = do_QueryInterface(request);
+    // Determine if we're uploading. Only use OMT onDataAvailable if not.
+    nsCOMPtr<nsIFile> localFile;
+    GetLocalFileFromURI(data->mFile, getter_AddRefs(localFile));
+    if (r && localFile) {
+      if (!mBackgroundQueue) {
+        NS_CreateBackgroundTaskQueue("WebBrowserPersist",
+                                     getter_AddRefs(mBackgroundQueue));
+      }
+      if (mBackgroundQueue) {
+        r->RetargetDeliveryTo(mBackgroundQueue);
+      }
+    }
+
+    // If PERSIST_FLAGS_AUTODETECT_APPLY_CONVERSION is set in mPersistFlags,
+    // try to determine whether this channel needs to apply Content-Encoding
+    // conversions.
+    NS_ASSERTION(
+        !((mPersistFlags & PERSIST_FLAGS_AUTODETECT_APPLY_CONVERSION) &&
+          (mPersistFlags & PERSIST_FLAGS_NO_CONVERSION)),
+        "Conflict in persist flags: both AUTODETECT and NO_CONVERSION set");
+    if (mPersistFlags & PERSIST_FLAGS_AUTODETECT_APPLY_CONVERSION)
+      SetApplyConversionIfNeeded(channel);
+
+    if (data->mCalcFileExt &&
+        !(mPersistFlags & PERSIST_FLAGS_DONT_CHANGE_FILENAMES)) {
+      nsCOMPtr<nsIURI> uriWithExt;
+      // this is the first point at which the server can tell us the mimetype
+      nsresult rv = CalculateAndAppendFileExt(
+          data->mFile, channel, data->mOriginalLocation, uriWithExt);
+      if (NS_SUCCEEDED(rv)) {
+        data->mFile = uriWithExt;
+      }
+
+      // now make filename conformant and unique
+      nsCOMPtr<nsIURI> uniqueFilenameURI;
+      rv = CalculateUniqueFilename(data->mFile, uniqueFilenameURI);
+      if (NS_SUCCEEDED(rv)) {
+        data->mFile = uniqueFilenameURI;
+      }
+
+      // The URIData entry is pointing to the old unfixed URI, so we need
+      // to update it.
+      nsCOMPtr<nsIURI> chanURI;
+      rv = channel->GetOriginalURI(getter_AddRefs(chanURI));
+      if (NS_SUCCEEDED(rv)) {
+        nsAutoCString spec;
+        chanURI->GetSpec(spec);
+        URIData* uridata;
+        if (mURIMap.Get(spec, &uridata)) {
+          uridata->mFile = data->mFile;
+        }
+      }
+    }
+
+    // compare uris and bail before we add to output map if they are equal
+    bool isEqual = false;
+    if (NS_SUCCEEDED(data->mFile->Equals(data->mOriginalLocation, &isEqual)) &&
+        isEqual) {
+      {
+        MutexAutoLock lock(mOutputMapMutex);
+        // remove from output map
+        mOutputMap.Remove(keyPtr);
+      }
+
+      // cancel; we don't need to know any more
+      // stop request will get called
+      request->Cancel(NS_BINDING_ABORTED);
+    }
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsWebBrowserPersist::OnStopRequest(nsIRequest* request,
+                                                 nsresult status) {
+  nsCOMPtr<nsISupports> keyPtr = do_QueryInterface(request);
+  OutputData* data = mOutputMap.Get(keyPtr);
+  if (data) {
+    if (NS_SUCCEEDED(mPersistResult) && NS_FAILED(status)) {
+      SendErrorStatusChange(true, status, request, data->mFile);
+    }
+
+    // If there is a stream ref and we weren't canceled,
+    // close it away from the main thread.
+    // We don't do this when there's an error/cancelation,
+    // because our consumer may try to delete the file, which will error
+    // if we're still holding on to it, so we have to close it pronto.
+    {
+      MutexAutoLock lock(data->mStreamMutex);
+      if (data->mStream && NS_SUCCEEDED(status) && !mCancel) {
+        if (!mBackgroundQueue) {
+          nsresult rv = NS_CreateBackgroundTaskQueue(
+              "WebBrowserPersist", getter_AddRefs(mBackgroundQueue));
+          if (NS_FAILED(rv)) {
+            return rv;
+          }
+        }
+        // Now steal the stream ref and close it away from the main thread,
+        // keeping the promise around so we don't finish before all files
+        // are flushed and closed.
+        mFileClosePromises.AppendElement(InvokeAsync(
+            mBackgroundQueue, __func__, [stream = std::move(data->mStream)]() {
+              nsresult rv = stream->Close();
+              // We don't care if closing failed; we don't care in the
+              // destructor either...
+              return ClosePromise::CreateAndResolve(rv, __func__);
+            }));
+      }
+    }
+    MutexAutoLock lock(mOutputMapMutex);
+    mOutputMap.Remove(keyPtr);
+  } else {
+    // if we didn't find the data in mOutputMap, try mUploadList
+    UploadData* upData = mUploadList.Get(keyPtr);
+    if (upData) {
+      mUploadList.Remove(keyPtr);
+    }
+  }
+
+  // Do more work.
+  SerializeNextFile();
+
+  if (mProgressListener) {
+    uint32_t stateFlags = nsIWebProgressListener::STATE_STOP |
+                          nsIWebProgressListener::STATE_IS_REQUEST;
+    if (!mSavingDocument) {
+      stateFlags |= nsIWebProgressListener::STATE_IS_NETWORK;
+    }
+    mProgressListener->OnStateChange(nullptr, request, stateFlags, status);
+  }
+
+  return NS_OK;
+}
+
+//*****************************************************************************
+// nsWebBrowserPersist::nsIStreamListener
+//*****************************************************************************
+
+// Note: this is supposed to (but not guaranteed to) fire on a background
+// thread when used to save to local disk (channels not using local files will
+// use the main thread).
+// (Read) Access to mOutputMap is guarded via mOutputMapMutex.
+// Access to individual OutputData::mStream is guarded via its mStreamMutex.
+// mCancel is atomic, as is mPersistFlags (accessed via MakeOutputStream).
+// If you end up touching this method and needing other member access, bear
+// this in mind.
+NS_IMETHODIMP
+nsWebBrowserPersist::OnDataAvailable(nsIRequest* request,
+                                     nsIInputStream* aIStream, uint64_t aOffset,
+                                     uint32_t aLength) {
+  // MOZ_ASSERT(!NS_IsMainThread()); // no guarantees, but it's likely.
+
+  bool cancel = mCancel;
+  if (!cancel) {
+    nsresult rv = NS_OK;
+    uint32_t bytesRemaining = aLength;
+
+    nsCOMPtr<nsIChannel> channel = do_QueryInterface(request);
+    NS_ENSURE_TRUE(channel, NS_ERROR_FAILURE);
+
+    MutexAutoLock lock(mOutputMapMutex);
+    nsCOMPtr<nsISupports> keyPtr = do_QueryInterface(request);
+    OutputData* data = mOutputMap.Get(keyPtr);
+    if (!data) {
+      // might be uploadData; consume necko's buffer and bail...
+      uint32_t n;
+      return aIStream->ReadSegments(NS_DiscardSegment, nullptr, aLength, &n);
+    }
+
+    bool readError = true;
+
+    MutexAutoLock streamLock(data->mStreamMutex);
+    // Make the output stream
+    if (!data->mStream) {
+      rv = MakeOutputStream(data->mFile, getter_AddRefs(data->mStream));
+      if (NS_FAILED(rv)) {
+        readError = false;
+        cancel = true;
+      }
+    }
+
+    // Read data from the input and write to the output
+    char buffer[8192];
+    uint32_t bytesRead;
+    while (!cancel && bytesRemaining) {
+      readError = true;
+      rv = aIStream->Read(buffer,
+                          std::min(uint32_t(sizeof(buffer)), bytesRemaining),
+                          &bytesRead);
+      if (NS_SUCCEEDED(rv)) {
+        readError = false;
+        // Write out the data until something goes wrong, or, it is
+        // all written.  We loop because for some errors (e.g., disk
+        // full), we get NS_OK with some bytes written, then an error.
+        // So, we want to write again in that case to get the actual
+        // error code.
+        const char* bufPtr = buffer;  // Where to write from.
+        while (NS_SUCCEEDED(rv) && bytesRead) {
+          uint32_t bytesWritten = 0;
+          rv = data->mStream->Write(bufPtr, bytesRead, &bytesWritten);
+          if (NS_SUCCEEDED(rv)) {
+            bytesRead -= bytesWritten;
+            bufPtr += bytesWritten;
+            bytesRemaining -= bytesWritten;
+            // Force an error if (for some reason) we get NS_OK but
+            // no bytes written.
+            if (!bytesWritten) {
+              rv = NS_ERROR_FAILURE;
+              cancel = true;
+            }
+          } else {
+            // Disaster - can't write out the bytes - disk full / permission?
+            cancel = true;
+          }
+        }
+      } else {
+        // Disaster - can't read the bytes - broken link / file error?
+        cancel = true;
+      }
+    }
+
+    int64_t channelContentLength = -1;
+    if (!cancel &&
+        NS_SUCCEEDED(channel->GetContentLength(&channelContentLength))) {
+      // if we get -1 at this point, we didn't get content-length header
+      // assume that we got all of the data and push what we have;
+      // that's the best we can do now
+      if ((-1 == channelContentLength) ||
+          ((channelContentLength - (aOffset + aLength)) == 0)) {
+        NS_WARNING_ASSERTION(
+            channelContentLength != -1,
+            "nsWebBrowserPersist::OnDataAvailable() no content length "
+            "header, pushing what we have");
+        // we're done with this pass; see if we need to do upload
+        nsAutoCString contentType;
+        channel->GetContentType(contentType);
+        // if we don't have the right type of output stream then it's a local
+        // file
+        nsCOMPtr<nsIStorageStream> storStream(do_QueryInterface(data->mStream));
+        if (storStream) {
+          data->mStream->Close();
+          data->mStream =
+              nullptr;  // null out stream so we don't close it later
+          MOZ_ASSERT(NS_IsMainThread(),
+                     "Uploads should be on the main thread.");
+          rv = StartUpload(storStream, data->mFile, contentType);
+          if (NS_FAILED(rv)) {
+            readError = false;
+            cancel = true;
+          }
+        }
+      }
+    }
+
+    // Notify listener if an error occurred.
+    if (cancel) {
+      RefPtr<nsIRequest> req = readError ? request : nullptr;
+      nsCOMPtr<nsIURI> file = data->mFile;
+      RefPtr<Runnable> errorOnMainThread = NS_NewRunnableFunction(
+          "nsWebBrowserPersist::SendErrorStatusChange",
+          [self = RefPtr{this}, req, file, readError, rv]() {
+            self->SendErrorStatusChange(readError, rv, req, file);
+          });
+      NS_DispatchToMainThread(errorOnMainThread);
+
+      // And end the download on the main thread.
+      nsCOMPtr<nsIRunnable> endOnMainThread = NewRunnableMethod<nsresult>(
+          "nsWebBrowserPersist::EndDownload", this,
+          &nsWebBrowserPersist::EndDownload, NS_BINDING_ABORTED);
+      NS_DispatchToMainThread(endOnMainThread);
+    }
+  }
+
+  return cancel ? NS_BINDING_ABORTED : NS_OK;
+}
+
+//*****************************************************************************
+// nsWebBrowserPersist::nsIThreadRetargetableStreamListener
+//*****************************************************************************
+
+NS_IMETHODIMP nsWebBrowserPersist::CheckListenerChain() { return NS_OK; }
+
+//*****************************************************************************
+// nsWebBrowserPersist::nsIProgressEventSink
+//*****************************************************************************
+
+NS_IMETHODIMP nsWebBrowserPersist::OnProgress(nsIRequest* request,
+                                              int64_t aProgress,
+                                              int64_t aProgressMax) {
+  if (!mProgressListener) {
+    return NS_OK;
+  }
+
+  // Store the progress of this request
+  nsCOMPtr<nsISupports> keyPtr = do_QueryInterface(request);
+  OutputData* data = mOutputMap.Get(keyPtr);
+  if (data) {
+    data->mSelfProgress = aProgress;
+    data->mSelfProgressMax = aProgressMax;
+  } else {
+    UploadData* upData = mUploadList.Get(keyPtr);
+    if (upData) {
+      upData->mSelfProgress = aProgress;
+      upData->mSelfProgressMax = aProgressMax;
+    }
+  }
+
+  // Notify listener of total progress
+  CalcTotalProgress();
+  if (mProgressListener2) {
+    mProgressListener2->OnProgressChange64(nullptr, request, aProgress,
+                                           aProgressMax, mTotalCurrentProgress,
+                                           mTotalMaxProgress);
+  } else {
+    // have to truncate 64-bit to 32bit
+    mProgressListener->OnProgressChange(
+        nullptr, request, uint64_t(aProgress), uint64_t(aProgressMax),
+        mTotalCurrentProgress, mTotalMaxProgress);
+  }
+
+  // If our progress listener implements nsIProgressEventSink,
+  // forward the notification
+  if (mEventSink) {
+    mEventSink->OnProgress(request, aProgress, aProgressMax);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsWebBrowserPersist::OnStatus(nsIRequest* request,
+                                            nsresult status,
+                                            const char16_t* statusArg) {
+  if (mProgressListener) {
+    // We need to filter out non-error error codes.
+    // Is the only NS_SUCCEEDED value NS_OK?
+    switch (status) {
+      case NS_NET_STATUS_RESOLVING_HOST:
+      case NS_NET_STATUS_RESOLVED_HOST:
+      case NS_NET_STATUS_CONNECTING_TO:
+      case NS_NET_STATUS_CONNECTED_TO:
+      case NS_NET_STATUS_TLS_HANDSHAKE_STARTING:
+      case NS_NET_STATUS_TLS_HANDSHAKE_ENDED:
+      case NS_NET_STATUS_SENDING_TO:
+      case NS_NET_STATUS_RECEIVING_FROM:
+      case NS_NET_STATUS_WAITING_FOR:
+      case NS_NET_STATUS_READING:
+      case NS_NET_STATUS_WRITING:
+        break;
+
+      default:
+        // Pass other notifications (for legitimate errors) along.
+        mProgressListener->OnStatusChange(nullptr, request, status, statusArg);
+        break;
+    }
+  }
+
+  // If our progress listener implements nsIProgressEventSink,
+  // forward the notification
+  if (mEventSink) {
+    mEventSink->OnStatus(request, status, statusArg);
+  }
+
+  return NS_OK;
+}
+
+//*****************************************************************************
+// nsWebBrowserPersist private methods
+//*****************************************************************************
+
+// Convert error info into proper message text and send OnStatusChange
+// notification to the web progress listener.
+nsresult nsWebBrowserPersist::SendErrorStatusChange(bool aIsReadError,
+                                                    nsresult aResult,
+                                                    nsIRequest* aRequest,
+                                                    nsIURI* aURI) {
+  NS_ENSURE_ARG_POINTER(aURI);
+
+  if (!mProgressListener) {
+    // Do nothing
+    return NS_OK;
+  }
+
+  // Get the file path or spec from the supplied URI
+  nsCOMPtr<nsIFile> file;
+  GetLocalFileFromURI(aURI, getter_AddRefs(file));
+  AutoTArray<nsString, 1> strings;
+  nsresult rv;
+  if (file) {
+    file->GetPath(*strings.AppendElement());
+  } else {
+    nsAutoCString fileurl;
+    rv = aURI->GetSpec(fileurl);
+    NS_ENSURE_SUCCESS(rv, rv);
+    CopyUTF8toUTF16(fileurl, *strings.AppendElement());
+  }
+
+  const char* msgId;
+  switch (aResult) {
+    case NS_ERROR_FILE_NAME_TOO_LONG:
+      // File name too long.
+      msgId = "fileNameTooLongError";
+      break;
+    case NS_ERROR_FILE_ALREADY_EXISTS:
+      // File exists with same name as directory.
+      msgId = "fileAlreadyExistsError";
+      break;
+    case NS_ERROR_FILE_NO_DEVICE_SPACE:
+      // Out of space on target volume.
+      msgId = "diskFull";
+      break;
+
+    case NS_ERROR_FILE_READ_ONLY:
+      // Attempt to write to read/only file.
+      msgId = "readOnly";
+      break;
+
+    case NS_ERROR_FILE_ACCESS_DENIED:
+      // Attempt to write without sufficient permissions.
+      msgId = "accessError";
+      break;
+
+    default:
+      // Generic read/write error message.
+      if (aIsReadError)
+        msgId = "readError";
+      else
+        msgId = "writeError";
+      break;
+  }
+  // Get properties file bundle and extract status string.
+  nsCOMPtr<nsIStringBundleService> s =
+      do_GetService(NS_STRINGBUNDLE_CONTRACTID, &rv);
+  NS_ENSURE_TRUE(NS_SUCCEEDED(rv) && s, NS_ERROR_FAILURE);
+
+  nsCOMPtr<nsIStringBundle> bundle;
+  rv = s->CreateBundle(kWebBrowserPersistStringBundle, getter_AddRefs(bundle));
+  NS_ENSURE_TRUE(NS_SUCCEEDED(rv) && bundle, NS_ERROR_FAILURE);
+
+  nsAutoString msgText;
+  rv = bundle->FormatStringFromName(msgId, strings, msgText);
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+
+  mProgressListener->OnStatusChange(nullptr, aRequest, aResult, msgText.get());
+
+  return NS_OK;
+}
+
+nsresult nsWebBrowserPersist::GetValidURIFromObject(nsISupports* aObject,
+                                                    nsIURI** aURI) const {
+  NS_ENSURE_ARG_POINTER(aObject);
+  NS_ENSURE_ARG_POINTER(aURI);
+
+  nsCOMPtr<nsIFile> objAsFile = do_QueryInterface(aObject);
+  if (objAsFile) {
+    return NS_NewFileURI(aURI, objAsFile);
+  }
+  nsCOMPtr<nsIURI> objAsURI = do_QueryInterface(aObject);
+  if (objAsURI) {
+    *aURI = objAsURI;
+    NS_ADDREF(*aURI);
+    return NS_OK;
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+/* static */
+nsresult nsWebBrowserPersist::GetLocalFileFromURI(nsIURI* aURI,
+                                                  nsIFile** aLocalFile) {
+  nsresult rv;
+
+  nsCOMPtr<nsIFileURL> fileURL = do_QueryInterface(aURI, &rv);
+  if (NS_FAILED(rv)) return rv;
+
+  nsCOMPtr<nsIFile> file;
+  rv = fileURL->GetFile(getter_AddRefs(file));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  file.forget(aLocalFile);
+  return NS_OK;
+}
+
+/* static */
+nsresult nsWebBrowserPersist::AppendPathToURI(nsIURI* aURI,
+                                              const nsAString& aPath,
+                                              nsCOMPtr<nsIURI>& aOutURI) {
+  NS_ENSURE_ARG_POINTER(aURI);
+
+  nsAutoCString newPath;
+  nsresult rv = aURI->GetPathQueryRef(newPath);
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+
+  // Append a forward slash if necessary
+  int32_t len = newPath.Length();
+  if (len > 0 && newPath.CharAt(len - 1) != '/') {
+    newPath.Append('/');
+  }
+
+  // Store the path back on the URI
+  AppendUTF16toUTF8(aPath, newPath);
+
+  return NS_MutateURI(aURI).SetPathQueryRef(newPath).Finalize(aOutURI);
+}
+
+nsresult nsWebBrowserPersist::SaveURIInternal(
+    nsIURI* aURI, nsIPrincipal* aTriggeringPrincipal,
+    nsContentPolicyType aContentPolicyType, uint32_t aCacheKey,
+    nsIReferrerInfo* aReferrerInfo, nsICookieJarSettings* aCookieJarSettings,
+    nsIInputStream* aPostData, const char* aExtraHeaders, nsIURI* aFile,
+    bool aCalcFileExt, bool aIsPrivate) {
+  NS_ENSURE_ARG_POINTER(aURI);
+  NS_ENSURE_ARG_POINTER(aFile);
+  NS_ENSURE_ARG_POINTER(aTriggeringPrincipal);
+
+  nsresult rv = NS_OK;
+
+  mURI = aURI;
+
+  nsLoadFlags loadFlags = nsIRequest::LOAD_NORMAL;
+  if (mPersistFlags & PERSIST_FLAGS_BYPASS_CACHE) {
+    loadFlags |= nsIRequest::LOAD_BYPASS_CACHE;
+  } else if (mPersistFlags & PERSIST_FLAGS_FROM_CACHE) {
+    loadFlags |= nsIRequest::LOAD_FROM_CACHE;
+  }
+
+  // If there is no cookieJarSetting given, we need to create a new
+  // cookieJarSettings for this download in order to send cookies based on the
+  // current state of the prefs/permissions.
+  nsCOMPtr<nsICookieJarSettings> cookieJarSettings = aCookieJarSettings;
+  if (!cookieJarSettings) {
+    // Although the variable is called 'triggering principal', it is used as the
+    // loading principal in the download channel, so we treat it as a loading
+    // principal also.
+    bool shouldResistFingerprinting =
+        nsContentUtils::ShouldResistFingerprinting_dangerous(
+            aTriggeringPrincipal,
+            "We are creating a new CookieJar Settings, so none exists "
+            "currently. Although the variable is called 'triggering principal',"
+            "it is used as the loading principal in the download channel, so we"
+            "treat it as a loading principal also.");
+    cookieJarSettings =
+        aIsPrivate
+            ? net::CookieJarSettings::Create(net::CookieJarSettings::ePrivate,
+                                             shouldResistFingerprinting)
+            : net::CookieJarSettings::Create(net::CookieJarSettings::eRegular,
+                                             shouldResistFingerprinting);
+  }
+
+  // Open a channel to the URI
+  nsCOMPtr<nsIChannel> inputChannel;
+  rv = NS_NewChannel(getter_AddRefs(inputChannel), aURI, aTriggeringPrincipal,
+                     nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_SEC_CONTEXT_IS_NULL,
+                     aContentPolicyType, cookieJarSettings,
+                     nullptr,  // aPerformanceStorage
+                     nullptr,  // aLoadGroup
+                     static_cast<nsIInterfaceRequestor*>(this), loadFlags);
+
+  nsCOMPtr<nsIPrivateBrowsingChannel> pbChannel =
+      do_QueryInterface(inputChannel);
+  if (pbChannel) {
+    pbChannel->SetPrivate(aIsPrivate);
+  }
+
+  if (NS_FAILED(rv) || inputChannel == nullptr) {
+    EndDownload(NS_ERROR_FAILURE);
+    return NS_ERROR_FAILURE;
+  }
+
+  // Disable content conversion
+  if (mPersistFlags & PERSIST_FLAGS_NO_CONVERSION) {
+    nsCOMPtr<nsIEncodedChannel> encodedChannel(do_QueryInterface(inputChannel));
+    if (encodedChannel) {
+      encodedChannel->SetApplyConversion(false);
+    }
+  }
+
+  nsCOMPtr<nsILoadInfo> loadInfo = inputChannel->LoadInfo();
+  loadInfo->SetIsUserTriggeredSave(true);
+
+  // Set the referrer, post data and headers if any
+  nsCOMPtr<nsIHttpChannel> httpChannel(do_QueryInterface(inputChannel));
+  if (httpChannel) {
+    if (aReferrerInfo) {
+      DebugOnly<nsresult> success = httpChannel->SetReferrerInfo(aReferrerInfo);
+      MOZ_ASSERT(NS_SUCCEEDED(success));
+    }
+
+    // Post data
+    if (aPostData) {
+      nsCOMPtr<nsISeekableStream> stream(do_QueryInterface(aPostData));
+      if (stream) {
+        // Rewind the postdata stream
+        stream->Seek(nsISeekableStream::NS_SEEK_SET, 0);
+        nsCOMPtr<nsIUploadChannel> uploadChannel(
+            do_QueryInterface(httpChannel));
+        NS_ASSERTION(uploadChannel, "http must support nsIUploadChannel");
+        // Attach the postdata to the http channel
+        uploadChannel->SetUploadStream(aPostData, ""_ns, -1);
+      }
+    }
+
+    // Cache key
+    nsCOMPtr<nsICacheInfoChannel> cacheChannel(do_QueryInterface(httpChannel));
+    if (cacheChannel && aCacheKey != 0) {
+      cacheChannel->SetCacheKey(aCacheKey);
+    }
+
+    // Headers
+    if (aExtraHeaders) {
+      nsAutoCString oneHeader;
+      nsAutoCString headerName;
+      nsAutoCString headerValue;
+      int32_t crlf = 0;
+      int32_t colon = 0;
+      const char* kWhitespace = "\b\t\r\n ";
+      nsAutoCString extraHeaders(aExtraHeaders);
+      while (true) {
+        crlf = extraHeaders.Find("\r\n");
+        if (crlf == -1) break;
+        extraHeaders.Mid(oneHeader, 0, crlf);
+        extraHeaders.Cut(0, crlf + 2);
+        colon = oneHeader.Find(":");
+        if (colon == -1) break;  // Should have a colon
+        oneHeader.Left(headerName, colon);
+        colon++;
+        oneHeader.Mid(headerValue, colon, oneHeader.Length() - colon);
+        headerName.Trim(kWhitespace);
+        headerValue.Trim(kWhitespace);
+        // Add the header (merging if required)
+        rv = httpChannel->SetRequestHeader(headerName, headerValue, true);
+        if (NS_FAILED(rv)) {
+          EndDownload(NS_ERROR_FAILURE);
+          return NS_ERROR_FAILURE;
+        }
+      }
+    }
+  }
+  return SaveChannelInternal(inputChannel, aFile, aCalcFileExt);
+}
+
+nsresult nsWebBrowserPersist::SaveChannelInternal(nsIChannel* aChannel,
+                                                  nsIURI* aFile,
+                                                  bool aCalcFileExt) {
+  NS_ENSURE_ARG_POINTER(aChannel);
+  NS_ENSURE_ARG_POINTER(aFile);
+
+  // The default behaviour of SaveChannelInternal is to download the source
+  // into a storage stream and upload that to the target. MakeOutputStream
+  // special-cases a file target and creates a file output stream directly.
+  // We want to special-case a file source and create a file input stream,
+  // but we don't need to do this in the case of a file target.
+  nsCOMPtr<nsIFileChannel> fc(do_QueryInterface(aChannel));
+  nsCOMPtr<nsIFileURL> fu(do_QueryInterface(aFile));
+
+  if (fc && !fu) {
+    nsCOMPtr<nsIInputStream> fileInputStream, bufferedInputStream;
+    nsresult rv = aChannel->Open(getter_AddRefs(fileInputStream));
+    NS_ENSURE_SUCCESS(rv, rv);
+    rv = NS_NewBufferedInputStream(getter_AddRefs(bufferedInputStream),
+                                   fileInputStream.forget(),
+                                   BUFFERED_OUTPUT_SIZE);
+    NS_ENSURE_SUCCESS(rv, rv);
+    nsAutoCString contentType;
+    aChannel->GetContentType(contentType);
+    return StartUpload(bufferedInputStream, aFile, contentType);
+  }
+
+  // Mark save channel as throttleable.
+  nsCOMPtr<nsIClassOfService> cos(do_QueryInterface(aChannel));
+  if (cos) {
+    cos->AddClassFlags(nsIClassOfService::Throttleable);
+  }
+
+  // Read from the input channel
+  nsresult rv = aChannel->AsyncOpen(this);
+  if (rv == NS_ERROR_NO_CONTENT) {
+    // Assume this is a protocol such as mailto: which does not feed out
+    // data and just ignore it.
+    return NS_SUCCESS_DONT_FIXUP;
+  }
+
+  if (NS_FAILED(rv)) {
+    // Opening failed, but do we care?
+    if (mPersistFlags & PERSIST_FLAGS_FAIL_ON_BROKEN_LINKS) {
+      SendErrorStatusChange(true, rv, aChannel, aFile);
+      EndDownload(NS_ERROR_FAILURE);
+      return NS_ERROR_FAILURE;
+    }
+    return NS_SUCCESS_DONT_FIXUP;
+  }
+
+  MutexAutoLock lock(mOutputMapMutex);
+  // Add the output transport to the output map with the channel as the key
+  nsCOMPtr<nsISupports> keyPtr = do_QueryInterface(aChannel);
+  mOutputMap.InsertOrUpdate(keyPtr,
+                            MakeUnique<OutputData>(aFile, mURI, aCalcFileExt));
+
+  return NS_OK;
+}
+
+nsresult nsWebBrowserPersist::GetExtensionForContentType(
+    const char16_t* aContentType, char16_t** aExt) {
+  NS_ENSURE_ARG_POINTER(aContentType);
+  NS_ENSURE_ARG_POINTER(aExt);
+
+  *aExt = nullptr;
+
+  nsresult rv;
+  if (!mMIMEService) {
+    mMIMEService = do_GetService(NS_MIMESERVICE_CONTRACTID, &rv);
+    NS_ENSURE_TRUE(mMIMEService, NS_ERROR_FAILURE);
+  }
+
+  nsAutoCString contentType;
+  LossyCopyUTF16toASCII(MakeStringSpan(aContentType), contentType);
+  nsAutoCString ext;
+  rv = mMIMEService->GetPrimaryExtension(contentType, ""_ns, ext);
+  if (NS_SUCCEEDED(rv)) {
+    *aExt = UTF8ToNewUnicode(ext);
+    NS_ENSURE_TRUE(*aExt, NS_ERROR_OUT_OF_MEMORY);
+    return NS_OK;
+  }
+
+  return NS_ERROR_FAILURE;
+}
+
+nsresult nsWebBrowserPersist::SaveDocumentDeferred(
+    mozilla::UniquePtr<WalkData>&& aData) {
+  nsresult rv =
+      SaveDocumentInternal(aData->mDocument, aData->mFile, aData->mDataPath);
+  if (NS_FAILED(rv)) {
+    SendErrorStatusChange(true, rv, nullptr, mURI);
+    EndDownload(rv);
+  }
+  return rv;
+}
+
+nsresult nsWebBrowserPersist::SaveDocumentInternal(
+    nsIWebBrowserPersistDocument* aDocument, nsIURI* aFile, nsIURI* aDataPath) {
+  mURI = nullptr;
+  NS_ENSURE_ARG_POINTER(aDocument);
+  NS_ENSURE_ARG_POINTER(aFile);
+
+  nsresult rv = aDocument->SetPersistFlags(mPersistFlags);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = aDocument->GetIsPrivate(&mIsPrivate);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // See if we can get the local file representation of this URI
+  nsCOMPtr<nsIFile> localFile;
+  rv = GetLocalFileFromURI(aFile, getter_AddRefs(localFile));
+
+  nsCOMPtr<nsIFile> localDataPath;
+  if (NS_SUCCEEDED(rv) && aDataPath) {
+    // See if we can get the local file representation of this URI
+    rv = GetLocalFileFromURI(aDataPath, getter_AddRefs(localDataPath));
+    NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+  }
+
+  // Persist the main document
+  rv = aDocument->GetCharacterSet(mCurrentCharset);
+  NS_ENSURE_SUCCESS(rv, rv);
+  nsAutoCString uriSpec;
+  rv = aDocument->GetDocumentURI(uriSpec);
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = NS_NewURI(getter_AddRefs(mURI), uriSpec, mCurrentCharset.get());
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = aDocument->GetBaseURI(uriSpec);
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = NS_NewURI(getter_AddRefs(mCurrentBaseURI), uriSpec,
+                 mCurrentCharset.get());
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Does the caller want to fixup the referenced URIs and save those too?
+  if (aDataPath) {
+    // Basic steps are these.
+    //
+    // 1. Iterate through the document (and subdocuments) building a list
+    //    of unique URIs.
+    // 2. For each URI create an OutputData entry and open a channel to save
+    //    it. As each URI is saved, discover the mime type and fix up the
+    //    local filename with the correct extension.
+    // 3. Store the document in a list and wait for URI persistence to finish
+    // 4. After URI persistence completes save the list of documents,
+    //    fixing it up as it goes out to file.
+
+    mCurrentDataPathIsRelative = false;
+    mCurrentDataPath = aDataPath;
+    mCurrentRelativePathToData = "";
+    mCurrentThingsToPersist = 0;
+    mTargetBaseURI = aFile;
+
+    // Determine if the specified data path is relative to the
+    // specified file, (e.g. c:\docs\htmldata is relative to
+    // c:\docs\myfile.htm, but not to d:\foo\data.
+
+    // Starting with the data dir work back through its parents
+    // checking if one of them matches the base directory.
+
+    if (localDataPath && localFile) {
+      nsCOMPtr<nsIFile> baseDir;
+      localFile->GetParent(getter_AddRefs(baseDir));
+
+      nsAutoCString relativePathToData;
+      nsCOMPtr<nsIFile> dataDirParent;
+      dataDirParent = localDataPath;
+      while (dataDirParent) {
+        bool sameDir = false;
+        dataDirParent->Equals(baseDir, &sameDir);
+        if (sameDir) {
+          mCurrentRelativePathToData = relativePathToData;
+          mCurrentDataPathIsRelative = true;
+          break;
+        }
+
+        nsAutoString dirName;
+        dataDirParent->GetLeafName(dirName);
+
+        nsAutoCString newRelativePathToData;
+        newRelativePathToData =
+            NS_ConvertUTF16toUTF8(dirName) + "/"_ns + relativePathToData;
+        relativePathToData = newRelativePathToData;
+
+        nsCOMPtr<nsIFile> newDataDirParent;
+        rv = dataDirParent->GetParent(getter_AddRefs(newDataDirParent));
+        dataDirParent = newDataDirParent;
+      }
+    } else {
+      // generate a relative path if possible
+      nsCOMPtr<nsIURL> pathToBaseURL(do_QueryInterface(aFile));
+      if (pathToBaseURL) {
+        nsAutoCString relativePath;  // nsACString
+        if (NS_SUCCEEDED(
+                pathToBaseURL->GetRelativeSpec(aDataPath, relativePath))) {
+          mCurrentDataPathIsRelative = true;
+          mCurrentRelativePathToData = relativePath;
+        }
+      }
+    }
+
+    // Store the document in a list so when URI persistence is done and the
+    // filenames of saved URIs are known, the documents can be fixed up and
+    // saved
+
+    auto* docData = new DocData;
+    docData->mBaseURI = mCurrentBaseURI;
+    docData->mCharset = mCurrentCharset;
+    docData->mDocument = aDocument;
+    docData->mFile = aFile;
+    mDocList.AppendElement(docData);
+
+    // Walk the DOM gathering a list of externally referenced URIs in the uri
+    // map
+    nsCOMPtr<nsIWebBrowserPersistResourceVisitor> visit =
+        new OnWalk(this, aFile, localDataPath);
+    return aDocument->ReadResources(visit);
+  } else {
+    auto* docData = new DocData;
+    docData->mBaseURI = mCurrentBaseURI;
+    docData->mCharset = mCurrentCharset;
+    docData->mDocument = aDocument;
+    docData->mFile = aFile;
+    mDocList.AppendElement(docData);
+
+    // Not walking DOMs, so go directly to serialization.
+    SerializeNextFile();
+    return NS_OK;
+  }
+}
+
+NS_IMETHODIMP
+nsWebBrowserPersist::OnWalk::VisitResource(
+    nsIWebBrowserPersistDocument* aDoc, const nsACString& aURI,
+    nsContentPolicyType aContentPolicyType) {
+  return mParent->StoreURI(aURI, aDoc, aContentPolicyType);
+}
+
+NS_IMETHODIMP
+nsWebBrowserPersist::OnWalk::VisitDocument(
+    nsIWebBrowserPersistDocument* aDoc, nsIWebBrowserPersistDocument* aSubDoc) {
+  URIData* data = nullptr;
+  nsAutoCString uriSpec;
+  nsresult rv = aSubDoc->GetDocumentURI(uriSpec);
+  NS_ENSURE_SUCCESS(rv, rv);
+  rv = mParent->StoreURI(uriSpec, aDoc, nsIContentPolicy::TYPE_SUBDOCUMENT,
+                         false, &data);
+  NS_ENSURE_SUCCESS(rv, rv);
+  if (!data) {
+    // If the URI scheme isn't persistable, then don't persist.
+    return NS_OK;
+  }
+  data->mIsSubFrame = true;
+  return mParent->SaveSubframeContent(aSubDoc, aDoc, uriSpec, data);
+}
+
+NS_IMETHODIMP
+nsWebBrowserPersist::OnWalk::VisitBrowsingContext(
+    nsIWebBrowserPersistDocument* aDoc, BrowsingContext* aContext) {
+  RefPtr<dom::CanonicalBrowsingContext> context = aContext->Canonical();
+
+  if (NS_WARN_IF(!context->GetCurrentWindowGlobal())) {
+    EndVisit(nullptr, NS_ERROR_FAILURE);
+    return NS_ERROR_FAILURE;
+  }
+
+  UniquePtr<WebBrowserPersistDocumentParent> actor(
+      new WebBrowserPersistDocumentParent());
+
+  nsCOMPtr<nsIWebBrowserPersistDocumentReceiver> receiver =
+      new OnRemoteWalk(this, aDoc);
+  actor->SetOnReady(receiver);
+
+  RefPtr<dom::BrowserParent> browserParent =
+      context->GetCurrentWindowGlobal()->GetBrowserParent();
+
+  bool ok =
+      context->GetContentParent()->SendPWebBrowserPersistDocumentConstructor(
+          actor.release(), browserParent, context);
+
+  if (NS_WARN_IF(!ok)) {
+    // (The actor will be destroyed on constructor failure.)
+    EndVisit(nullptr, NS_ERROR_FAILURE);
+    return NS_ERROR_FAILURE;
+  }
+
+  ++mPendingDocuments;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsWebBrowserPersist::OnWalk::EndVisit(nsIWebBrowserPersistDocument* aDoc,
+                                      nsresult aStatus) {
+  if (NS_FAILED(mStatus)) {
+    return mStatus;
+  }
+
+  if (NS_FAILED(aStatus)) {
+    mStatus = aStatus;
+    mParent->SendErrorStatusChange(true, aStatus, nullptr, mFile);
+    mParent->EndDownload(aStatus);
+    return aStatus;
+  }
+
+  if (--mPendingDocuments) {
+    // We're not done yet, wait for more.
+    return NS_OK;
+  }
+
+  mParent->FinishSaveDocumentInternal(mFile, mDataPath);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsWebBrowserPersist::OnRemoteWalk::OnDocumentReady(
+    nsIWebBrowserPersistDocument* aSubDocument) {
+  mVisitor->VisitDocument(mDocument, aSubDocument);
+  mVisitor->EndVisit(mDocument, NS_OK);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsWebBrowserPersist::OnRemoteWalk::OnError(nsresult aFailure) {
+  mVisitor->EndVisit(nullptr, aFailure);
+  return NS_OK;
+}
+
+void nsWebBrowserPersist::FinishSaveDocumentInternal(nsIURI* aFile,
+                                                     nsIFile* aDataPath) {
+  // If there are things to persist, create a directory to hold them
+  if (mCurrentThingsToPersist > 0) {
+    if (aDataPath) {
+      bool exists = false;
+      bool haveDir = false;
+
+      aDataPath->Exists(&exists);
+      if (exists) {
+        aDataPath->IsDirectory(&haveDir);
+      }
+      if (!haveDir) {
+        nsresult rv = aDataPath->Create(nsIFile::DIRECTORY_TYPE, 0755);
+        if (NS_SUCCEEDED(rv)) {
+          haveDir = true;
+        } else {
+          SendErrorStatusChange(false, rv, nullptr, aFile);
+        }
+      }
+      if (!haveDir) {
+        EndDownload(NS_ERROR_FAILURE);
+        return;
+      }
+      if (mPersistFlags & PERSIST_FLAGS_CLEANUP_ON_FAILURE) {
+        // Add to list of things to delete later if all goes wrong
+        auto* cleanupData = new CleanupData;
+        cleanupData->mFile = aDataPath;
+        cleanupData->mIsDirectory = true;
+        mCleanupList.AppendElement(cleanupData);
+      }
+    }
+  }
+
+  if (mWalkStack.Length() > 0) {
+    mozilla::UniquePtr<WalkData> toWalk = mWalkStack.PopLastElement();
+    // Bounce this off the event loop to avoid stack overflow.
+    using WalkStorage = StoreCopyPassByRRef<decltype(toWalk)>;
+    auto saveMethod = &nsWebBrowserPersist::SaveDocumentDeferred;
+    nsCOMPtr<nsIRunnable> saveLater = NewRunnableMethod<WalkStorage>(
+        "nsWebBrowserPersist::FinishSaveDocumentInternal", this, saveMethod,
+        std::move(toWalk));
+    NS_DispatchToCurrentThread(saveLater);
+  } else {
+    // Done walking DOMs; on to the serialization phase.
+    SerializeNextFile();
+  }
+}
+
+void nsWebBrowserPersist::Cleanup() {
+  mURIMap.Clear();
+  nsClassHashtable<nsISupportsHashKey, OutputData> outputMapCopy;
+  {
+    MutexAutoLock lock(mOutputMapMutex);
+    mOutputMap.SwapElements(outputMapCopy);
+  }
+  for (const auto& key : outputMapCopy.Keys()) {
+    nsCOMPtr<nsIChannel> channel = do_QueryInterface(key);
+    if (channel) {
+      channel->Cancel(NS_BINDING_ABORTED);
+    }
+  }
+  outputMapCopy.Clear();
+
+  for (const auto& key : mUploadList.Keys()) {
+    nsCOMPtr<nsIChannel> channel = do_QueryInterface(key);
+    if (channel) {
+      channel->Cancel(NS_BINDING_ABORTED);
+    }
+  }
+  mUploadList.Clear();
+
+  uint32_t i;
+  for (i = 0; i < mDocList.Length(); i++) {
+    DocData* docData = mDocList.ElementAt(i);
+    delete docData;
+  }
+  mDocList.Clear();
+
+  for (i = 0; i < mCleanupList.Length(); i++) {
+    CleanupData* cleanupData = mCleanupList.ElementAt(i);
+    delete cleanupData;
+  }
+  mCleanupList.Clear();
+
+  mFilenameList.Clear();
+}
+
+void nsWebBrowserPersist::CleanupLocalFiles() {
+  // Two passes, the first pass cleans up files, the second pass tests
+  // for and then deletes empty directories. Directories that are not
+  // empty after the first pass must contain files from something else
+  // and are not deleted.
+  int pass;
+  for (pass = 0; pass < 2; pass++) {
+    uint32_t i;
+    for (i = 0; i < mCleanupList.Length(); i++) {
+      CleanupData* cleanupData = mCleanupList.ElementAt(i);
+      nsCOMPtr<nsIFile> file = cleanupData->mFile;
+
+      // Test if the dir / file exists (something in an earlier loop
+      // may have already removed it)
+      bool exists = false;
+      file->Exists(&exists);
+      if (!exists) continue;
+
+      // Test if the file has changed in between creation and deletion
+      // in some way that means it should be ignored
+      bool isDirectory = false;
+      file->IsDirectory(&isDirectory);
+      if (isDirectory != cleanupData->mIsDirectory)
+        continue;  // A file has become a dir or vice versa !
+
+      if (pass == 0 && !isDirectory) {
+        file->Remove(false);
+      } else if (pass == 1 && isDirectory)  // Directory
+      {
+        // Directories are more complicated. Enumerate through
+        // children looking for files. Any files created by the
+        // persist object would have been deleted by the first
+        // pass so if there are any there at this stage, the dir
+        // cannot be deleted because it has someone else's files
+        // in it. Empty child dirs are deleted but they must be
+        // recursed through to ensure they are actually empty.
+
+        bool isEmptyDirectory = true;
+        nsCOMArray<nsIDirectoryEnumerator> dirStack;
+        int32_t stackSize = 0;
+
+        // Push the top level enum onto the stack
+        nsCOMPtr<nsIDirectoryEnumerator> pos;
+        if (NS_SUCCEEDED(file->GetDirectoryEntries(getter_AddRefs(pos))))
+          dirStack.AppendObject(pos);
+
+        while (isEmptyDirectory && (stackSize = dirStack.Count())) {
+          // Pop the last element
+          nsCOMPtr<nsIDirectoryEnumerator> curPos;
+          curPos = dirStack[stackSize - 1];
+          dirStack.RemoveObjectAt(stackSize - 1);
+
+          nsCOMPtr<nsIFile> child;
+          if (NS_FAILED(curPos->GetNextFile(getter_AddRefs(child))) || !child) {
+            continue;
+          }
+
+          bool childIsSymlink = false;
+          child->IsSymlink(&childIsSymlink);
+          bool childIsDir = false;
+          child->IsDirectory(&childIsDir);
+          if (!childIsDir || childIsSymlink) {
+            // Some kind of file or symlink which means dir
+            // is not empty so just drop out.
+            isEmptyDirectory = false;
+            break;
+          }
+          // Push parent enumerator followed by child enumerator
+          nsCOMPtr<nsIDirectoryEnumerator> childPos;
+          child->GetDirectoryEntries(getter_AddRefs(childPos));
+          dirStack.AppendObject(curPos);
+          if (childPos) dirStack.AppendObject(childPos);
+        }
+        dirStack.Clear();
+
+        // If after all that walking the dir is deemed empty, delete it
+        if (isEmptyDirectory) {
+          file->Remove(true);
+        }
+      }
+    }
+  }
+}
+
+nsresult nsWebBrowserPersist::CalculateUniqueFilename(
+    nsIURI* aURI, nsCOMPtr<nsIURI>& aOutURI) {
+  nsCOMPtr<nsIURL> url(do_QueryInterface(aURI));
+  NS_ENSURE_TRUE(url, NS_ERROR_FAILURE);
+
+  bool nameHasChanged = false;
+  nsresult rv;
+
+  // Get the old filename
+  nsAutoCString filename;
+  rv = url->GetFileName(filename);
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+  nsAutoCString directory;
+  rv = url->GetDirectory(directory);
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+
+  // Split the filename into a base and an extension.
+  // e.g. "foo.html" becomes "foo" & ".html"
+  //
+  // The nsIURL methods GetFileBaseName & GetFileExtension don't
+  // preserve the dot whereas this code does to save some effort
+  // later when everything is put back together.
+  int32_t lastDot = filename.RFind(".");
+  nsAutoCString base;
+  nsAutoCString ext;
+  if (lastDot >= 0) {
+    filename.Mid(base, 0, lastDot);
+    filename.Mid(ext, lastDot, filename.Length() - lastDot);  // includes dot
+  } else {
+    // filename contains no dot
+    base = filename;
+  }
+
+  // Test if the filename is longer than allowed by the OS
+  int32_t needToChop = filename.Length() - kDefaultMaxFilenameLength;
+  if (needToChop > 0) {
+    // Truncate the base first and then the ext if necessary
+    if (base.Length() > (uint32_t)needToChop) {
+      base.Truncate(base.Length() - needToChop);
+    } else {
+      needToChop -= base.Length() - 1;
+      base.Truncate(1);
+      if (ext.Length() > (uint32_t)needToChop) {
+        ext.Truncate(ext.Length() - needToChop);
+      } else {
+        ext.Truncate(0);
+      }
+      // If kDefaultMaxFilenameLength were 1 we'd be in trouble here,
+      // but that won't happen because it will be set to a sensible
+      // value.
+    }
+
+    filename.Assign(base);
+    filename.Append(ext);
+    nameHasChanged = true;
+  }
+
+  // Ensure the filename is unique
+  // Create a filename if it's empty, or if the filename / datapath is
+  // already taken by another URI and create an alternate name.
+
+  if (base.IsEmpty() || !mFilenameList.IsEmpty()) {
+    nsAutoCString tmpPath;
+    nsAutoCString tmpBase;
+    uint32_t duplicateCounter = 1;
+    while (true) {
+      // Make a file name,
+      // Foo become foo_001, foo_002, etc.
+      // Empty files become _001, _002 etc.
+
+      if (base.IsEmpty() || duplicateCounter > 1) {
+        SmprintfPointer tmp = mozilla::Smprintf("_%03d", duplicateCounter);
+        NS_ENSURE_TRUE(tmp, NS_ERROR_OUT_OF_MEMORY);
+        if (filename.Length() < kDefaultMaxFilenameLength - 4) {
+          tmpBase = base;
+        } else {
+          base.Mid(tmpBase, 0, base.Length() - 4);
+        }
+        tmpBase.Append(tmp.get());
+      } else {
+        tmpBase = base;
+      }
+
+      tmpPath.Assign(directory);
+      tmpPath.Append(tmpBase);
+      tmpPath.Append(ext);
+
+      // Test if the name is a duplicate
+      if (!mFilenameList.Contains(tmpPath)) {
+        if (!base.Equals(tmpBase)) {
+          filename.Assign(tmpBase);
+          filename.Append(ext);
+          nameHasChanged = true;
+        }
+        break;
+      }
+      duplicateCounter++;
+    }
+  }
+
+  // Add name to list of those already used
+  nsAutoCString newFilepath(directory);
+  newFilepath.Append(filename);
+  mFilenameList.AppendElement(newFilepath);
+
+  // Update the uri accordingly if the filename actually changed
+  if (nameHasChanged) {
+    // Final sanity test
+    if (filename.Length() > kDefaultMaxFilenameLength) {
+      NS_WARNING(
+          "Filename wasn't truncated less than the max file length - how can "
+          "that be?");
+      return NS_ERROR_FAILURE;
+    }
+
+    nsCOMPtr<nsIFile> localFile;
+    GetLocalFileFromURI(aURI, getter_AddRefs(localFile));
+
+    if (localFile) {
+      nsAutoString filenameAsUnichar;
+      CopyASCIItoUTF16(filename, filenameAsUnichar);
+      localFile->SetLeafName(filenameAsUnichar);
+
+      // Resync the URI with the file after the extension has been appended
+      return NS_MutateURI(aURI)
+          .Apply(&nsIFileURLMutator::SetFile, localFile)
+          .Finalize(aOutURI);
+    }
+    return NS_MutateURI(url)
+        .Apply(&nsIURLMutator::SetFileName, filename, nullptr)
+        .Finalize(aOutURI);
+  }
+
+  // TODO (:valentin) This method should always clone aURI
+  aOutURI = aURI;
+  return NS_OK;
+}
+
+nsresult nsWebBrowserPersist::MakeFilenameFromURI(nsIURI* aURI,
+                                                  nsString& aFilename) {
+  // Try to get filename from the URI.
+  nsAutoString fileName;
+
+  // Get a suggested file name from the URL but strip it of characters
+  // likely to cause the name to be illegal.
+
+  nsCOMPtr<nsIURL> url(do_QueryInterface(aURI));
+  if (url) {
+    nsAutoCString nameFromURL;
+    url->GetFileName(nameFromURL);
+    if (mPersistFlags & PERSIST_FLAGS_DONT_CHANGE_FILENAMES) {
+      CopyASCIItoUTF16(NS_UnescapeURL(nameFromURL), fileName);
+      aFilename = fileName;
+      return NS_OK;
+    }
+    if (!nameFromURL.IsEmpty()) {
+      // Unescape the file name (GetFileName escapes it)
+      NS_UnescapeURL(nameFromURL);
+      uint32_t nameLength = 0;
+      const char* p = nameFromURL.get();
+      for (; *p && *p != ';' && *p != '?' && *p != '#' && *p != '.'; p++) {
+        if (IsAsciiAlpha(*p) || IsAsciiDigit(*p) || *p == '.' || *p == '-' ||
+            *p == '_' || (*p == ' ')) {
+          fileName.Append(char16_t(*p));
+          if (++nameLength == kDefaultMaxFilenameLength) {
+            // Note:
+            // There is no point going any further since it will be
+            // truncated in CalculateUniqueFilename anyway.
+            // More importantly, certain implementations of
+            // nsIFile (e.g. the Mac impl) might truncate
+            // names in undesirable ways, such as truncating from
+            // the middle, inserting ellipsis and so on.
+            break;
+          }
+        }
+      }
+    }
+  }
+
+  // Empty filenames can confuse the local file object later
+  // when it attempts to set the leaf name in CalculateUniqueFilename
+  // for duplicates and ends up replacing the parent dir. To avoid
+  // the problem, all filenames are made at least one character long.
+  if (fileName.IsEmpty()) {
+    fileName.Append(char16_t('a'));  // 'a' is for arbitrary
+  }
+
+  aFilename = fileName;
+  return NS_OK;
+}
+
+nsresult nsWebBrowserPersist::CalculateAndAppendFileExt(
+    nsIURI* aURI, nsIChannel* aChannel, nsIURI* aOriginalURIWithExtension,
+    nsCOMPtr<nsIURI>& aOutURI) {
+  nsresult rv = NS_OK;
+
+  if (!mMIMEService) {
+    mMIMEService = do_GetService(NS_MIMESERVICE_CONTRACTID, &rv);
+    NS_ENSURE_TRUE(mMIMEService, NS_ERROR_FAILURE);
+  }
+
+  nsAutoCString contentType;
+
+  // Get the content type from the channel
+  aChannel->GetContentType(contentType);
+
+  // Get the content type from the MIME service
+  if (contentType.IsEmpty()) {
+    nsCOMPtr<nsIURI> uri;
+    aChannel->GetOriginalURI(getter_AddRefs(uri));
+    mMIMEService->GetTypeFromURI(uri, contentType);
+  }
+
+  // Validate the filename
+  if (!contentType.IsEmpty()) {
+    nsAutoString newFileName;
+    if (NS_SUCCEEDED(mMIMEService->GetValidFileName(
+            aChannel, contentType, aOriginalURIWithExtension,
+            nsIMIMEService::VALIDATE_DEFAULT, newFileName))) {
+      nsCOMPtr<nsIFile> localFile;
+      GetLocalFileFromURI(aURI, getter_AddRefs(localFile));
+      if (localFile) {
+        localFile->SetLeafName(newFileName);
+
+        // Resync the URI with the file after the extension has been appended
+        return NS_MutateURI(aURI)
+            .Apply(&nsIFileURLMutator::SetFile, localFile)
+            .Finalize(aOutURI);
+      }
+      return NS_MutateURI(aURI)
+          .Apply(&nsIURLMutator::SetFileName,
+                 NS_ConvertUTF16toUTF8(newFileName), nullptr)
+          .Finalize(aOutURI);
+    }
+  }
+
+  // TODO (:valentin) This method should always clone aURI
+  aOutURI = aURI;
+  return NS_OK;
+}
+
+// Note: the MakeOutputStream helpers can be called from a background thread.
+nsresult nsWebBrowserPersist::MakeOutputStream(
+    nsIURI* aURI, nsIOutputStream** aOutputStream) {
+  nsresult rv;
+
+  nsCOMPtr<nsIFile> localFile;
+  GetLocalFileFromURI(aURI, getter_AddRefs(localFile));
+  if (localFile)
+    rv = MakeOutputStreamFromFile(localFile, aOutputStream);
+  else
+    rv = MakeOutputStreamFromURI(aURI, aOutputStream);
+
+  return rv;
+}
+
+nsresult nsWebBrowserPersist::MakeOutputStreamFromFile(
+    nsIFile* aFile, nsIOutputStream** aOutputStream) {
+  nsresult rv = NS_OK;
+
+  nsCOMPtr<nsIFileOutputStream> fileOutputStream =
+      do_CreateInstance(NS_LOCALFILEOUTPUTSTREAM_CONTRACTID, &rv);
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+
+  // XXX brade:  get the right flags here!
+  int32_t ioFlags = -1;
+  if (mPersistFlags & nsIWebBrowserPersist::PERSIST_FLAGS_APPEND_TO_FILE)
+    ioFlags = PR_APPEND | PR_CREATE_FILE | PR_WRONLY;
+  rv = fileOutputStream->Init(aFile, ioFlags, -1, 0);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = NS_NewBufferedOutputStream(aOutputStream, fileOutputStream.forget(),
+                                  BUFFERED_OUTPUT_SIZE);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (mPersistFlags & PERSIST_FLAGS_CLEANUP_ON_FAILURE) {
+    // Add to cleanup list in event of failure
+    auto* cleanupData = new CleanupData;
+    cleanupData->mFile = aFile;
+    cleanupData->mIsDirectory = false;
+    if (NS_IsMainThread()) {
+      mCleanupList.AppendElement(cleanupData);
+    } else {
+      // If we're on a background thread, add the cleanup back on the main
+      // thread.
+      RefPtr<Runnable> addCleanup = NS_NewRunnableFunction(
+          "nsWebBrowserPersist::AddCleanupToList",
+          [self = RefPtr{this}, cleanup = std::move(cleanupData)]() {
+            self->mCleanupList.AppendElement(cleanup);
+          });
+      NS_DispatchToMainThread(addCleanup);
+    }
+  }
+
+  return NS_OK;
+}
+
+nsresult nsWebBrowserPersist::MakeOutputStreamFromURI(
+    nsIURI* aURI, nsIOutputStream** aOutputStream) {
+  uint32_t segsize = 8192;
+  uint32_t maxsize = uint32_t(-1);
+  nsCOMPtr<nsIStorageStream> storStream;
+  nsresult rv =
+      NS_NewStorageStream(segsize, maxsize, getter_AddRefs(storStream));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  NS_ENSURE_SUCCESS(CallQueryInterface(storStream, aOutputStream),
+                    NS_ERROR_FAILURE);
+  return NS_OK;
+}
+
+void nsWebBrowserPersist::FinishDownload() {
+  // We call FinishDownload when we run out of things to download for this
+  // persist operation, by dispatching this method to the main thread. By now,
+  // it's possible that we have been canceled or encountered an error earlier
+  // in the download, or something else called EndDownload. In that case, don't
+  // re-run EndDownload.
+  if (mEndCalled) {
+    return;
+  }
+  EndDownload(NS_OK);
+}
+
+void nsWebBrowserPersist::EndDownload(nsresult aResult) {
+  MOZ_ASSERT(NS_IsMainThread(), "Should end download on the main thread.");
+
+  // Really this should just never happen, but if it does, at least avoid
+  // no-op notifications or pretending we succeeded if we already failed.
+  if (mEndCalled && (NS_SUCCEEDED(aResult) || mPersistResult == aResult)) {
+    return;
+  }
+
+  // Store the error code in the result if it is an error
+  if (NS_SUCCEEDED(mPersistResult) && NS_FAILED(aResult)) {
+    mPersistResult = aResult;
+  }
+
+  if (mEndCalled) {
+    MOZ_ASSERT(!mEndCalled, "Should only end the download once.");
+    return;
+  }
+  mEndCalled = true;
+
+  ClosePromise::All(GetCurrentSerialEventTarget(), mFileClosePromises)
+      ->Then(GetCurrentSerialEventTarget(), __func__,
+             [self = RefPtr{this}, aResult]() {
+               self->EndDownloadInternal(aResult);
+             });
+}
+
+void nsWebBrowserPersist::EndDownloadInternal(nsresult aResult) {
+  // mCompleted needs to be set before issuing the stop notification.
+  // (Bug 1224437)
+  mCompleted = true;
+  // State stop notification
+  if (mProgressListener) {
+    mProgressListener->OnStateChange(
+        nullptr, nullptr,
+        nsIWebProgressListener::STATE_STOP |
+            nsIWebProgressListener::STATE_IS_NETWORK,
+        mPersistResult);
+  }
+
+  // Do file cleanup if required
+  if (NS_FAILED(aResult) &&
+      (mPersistFlags & PERSIST_FLAGS_CLEANUP_ON_FAILURE)) {
+    CleanupLocalFiles();
+  }
+
+  // Cleanup the channels
+  Cleanup();
+
+  mProgressListener = nullptr;
+  mProgressListener2 = nullptr;
+  mEventSink = nullptr;
+}
+
+nsresult nsWebBrowserPersist::FixRedirectedChannelEntry(
+    nsIChannel* aNewChannel) {
+  NS_ENSURE_ARG_POINTER(aNewChannel);
+
+  // Iterate through existing open channels looking for one with a URI
+  // matching the one specified.
+  nsCOMPtr<nsIURI> originalURI;
+  aNewChannel->GetOriginalURI(getter_AddRefs(originalURI));
+  nsISupports* matchingKey = nullptr;
+  for (nsISupports* key : mOutputMap.Keys()) {
+    nsCOMPtr<nsIChannel> thisChannel = do_QueryInterface(key);
+    nsCOMPtr<nsIURI> thisURI;
+
+    thisChannel->GetOriginalURI(getter_AddRefs(thisURI));
+
+    // Compare this channel's URI to the one passed in.
+    bool matchingURI = false;
+    thisURI->Equals(originalURI, &matchingURI);
+    if (matchingURI) {
+      matchingKey = key;
+      break;
+    }
+  }
+
+  if (matchingKey) {
+    // We only get called from OnStartRequest, so this is always on the
+    // main thread. Make sure we don't pull the rug from under anything else.
+    MutexAutoLock lock(mOutputMapMutex);
+    // If a match was found, remove the data entry with the old channel
+    // key and re-add it with the new channel key.
+    mozilla::UniquePtr<OutputData> outputData;
+    mOutputMap.Remove(matchingKey, &outputData);
+    NS_ENSURE_TRUE(outputData, NS_ERROR_FAILURE);
+
+    // Store data again with new channel unless told to ignore redirects.
+    if (!(mPersistFlags & PERSIST_FLAGS_IGNORE_REDIRECTED_DATA)) {
+      nsCOMPtr<nsISupports> keyPtr = do_QueryInterface(aNewChannel);
+      mOutputMap.InsertOrUpdate(keyPtr, std::move(outputData));
+    }
+  }
+
+  return NS_OK;
+}
+
+void nsWebBrowserPersist::CalcTotalProgress() {
+  mTotalCurrentProgress = 0;
+  mTotalMaxProgress = 0;
+
+  if (mOutputMap.Count() > 0) {
+    // Total up the progress of each output stream
+    for (const auto& data : mOutputMap.Values()) {
+      // Only count toward total progress if destination file is local.
+      nsCOMPtr<nsIFileURL> fileURL = do_QueryInterface(data->mFile);
+      if (fileURL) {
+        mTotalCurrentProgress += data->mSelfProgress;
+        mTotalMaxProgress += data->mSelfProgressMax;
+      }
+    }
+  }
+
+  if (mUploadList.Count() > 0) {
+    // Total up the progress of each upload
+    for (const auto& data : mUploadList.Values()) {
+      if (data) {
+        mTotalCurrentProgress += data->mSelfProgress;
+        mTotalMaxProgress += data->mSelfProgressMax;
+      }
+    }
+  }
+
+  // XXX this code seems pretty bogus and pointless
+  if (mTotalCurrentProgress == 0 && mTotalMaxProgress == 0) {
+    // No output streams so we must be complete
+    mTotalCurrentProgress = 10000;
+    mTotalMaxProgress = 10000;
+  }
+}
+
+nsresult nsWebBrowserPersist::StoreURI(const nsACString& aURI,
+                                       nsIWebBrowserPersistDocument* aDoc,
+                                       nsContentPolicyType aContentPolicyType,
+                                       bool aNeedsPersisting, URIData** aData) {
+  nsCOMPtr<nsIURI> uri;
+  nsresult rv = NS_NewURI(getter_AddRefs(uri), aURI, mCurrentCharset.get(),
+                          mCurrentBaseURI);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return StoreURI(uri, aDoc, aContentPolicyType, aNeedsPersisting, aData);
+}
+
+nsresult nsWebBrowserPersist::StoreURI(nsIURI* aURI,
+                                       nsIWebBrowserPersistDocument* aDoc,
+                                       nsContentPolicyType aContentPolicyType,
+                                       bool aNeedsPersisting, URIData** aData) {
+  NS_ENSURE_ARG_POINTER(aURI);
+  if (aData) {
+    *aData = nullptr;
+  }
+
+  // Test if this URI should be persisted. By default
+  // we should assume the URI  is persistable.
+  bool doNotPersistURI;
+  nsresult rv = NS_URIChainHasFlags(
+      aURI, nsIProtocolHandler::URI_NON_PERSISTABLE, &doNotPersistURI);
+  if (NS_FAILED(rv)) {
+    doNotPersistURI = false;
+  }
+
+  if (doNotPersistURI) {
+    return NS_OK;
+  }
+
+  URIData* data = nullptr;
+  MakeAndStoreLocalFilenameInURIMap(aURI, aDoc, aContentPolicyType,
+                                    aNeedsPersisting, &data);
+  if (aData) {
+    *aData = data;
+  }
+
+  return NS_OK;
+}
+
+nsresult nsWebBrowserPersist::URIData::GetLocalURI(nsIURI* targetBaseURI,
+                                                   nsCString& aSpecOut) {
+  aSpecOut.SetIsVoid(true);
+  if (!mNeedsFixup) {
+    return NS_OK;
+  }
+  nsresult rv;
+  nsCOMPtr<nsIURI> fileAsURI;
+  if (mFile) {
+    fileAsURI = mFile;
+  } else {
+    fileAsURI = mDataPath;
+    rv = AppendPathToURI(fileAsURI, mFilename, fileAsURI);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  // remove username/password if present
+  Unused << NS_MutateURI(fileAsURI).SetUserPass(""_ns).Finalize(fileAsURI);
+
+  // reset node attribute
+  // Use relative or absolute links
+  if (mDataPathIsRelative) {
+    bool isEqual = false;
+    if (NS_SUCCEEDED(mRelativeDocumentURI->Equals(targetBaseURI, &isEqual)) &&
+        isEqual) {
+      nsCOMPtr<nsIURL> url(do_QueryInterface(fileAsURI));
+      if (!url) {
+        return NS_ERROR_FAILURE;
+      }
+
+      nsAutoCString filename;
+      url->GetFileName(filename);
+
+      nsAutoCString rawPathURL(mRelativePathToData);
+      rawPathURL.Append(filename);
+
+      rv = NS_EscapeURL(rawPathURL, esc_FilePath, aSpecOut, fallible);
+      NS_ENSURE_SUCCESS(rv, rv);
+    } else {
+      nsAutoCString rawPathURL;
+
+      nsCOMPtr<nsIFile> dataFile;
+      rv = GetLocalFileFromURI(mFile, getter_AddRefs(dataFile));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      nsCOMPtr<nsIFile> docFile;
+      rv = GetLocalFileFromURI(targetBaseURI, getter_AddRefs(docFile));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      nsCOMPtr<nsIFile> parentDir;
+      rv = docFile->GetParent(getter_AddRefs(parentDir));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = dataFile->GetRelativePath(parentDir, rawPathURL);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      rv = NS_EscapeURL(rawPathURL, esc_FilePath, aSpecOut, fallible);
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+  } else {
+    fileAsURI->GetSpec(aSpecOut);
+  }
+  if (mIsSubFrame) {
+    AppendUTF16toUTF8(mSubFrameExt, aSpecOut);
+  }
+
+  return NS_OK;
+}
+
+bool nsWebBrowserPersist::DocumentEncoderExists(const char* aContentType) {
+  return do_getDocumentTypeSupportedForEncoding(aContentType);
+}
+
+nsresult nsWebBrowserPersist::SaveSubframeContent(
+    nsIWebBrowserPersistDocument* aFrameContent,
+    nsIWebBrowserPersistDocument* aParentDocument, const nsCString& aURISpec,
+    URIData* aData) {
+  NS_ENSURE_ARG_POINTER(aData);
+
+  // Extract the content type for the frame's contents.
+  nsAutoCString contentType;
+  nsresult rv = aFrameContent->GetContentType(contentType);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsString ext;
+  GetExtensionForContentType(NS_ConvertASCIItoUTF16(contentType).get(),
+                             getter_Copies(ext));
+
+  // We must always have an extension so we will try to re-assign
+  // the original extension if GetExtensionForContentType fails.
+  if (ext.IsEmpty()) {
+    nsCOMPtr<nsIURI> docURI;
+    rv = NS_NewURI(getter_AddRefs(docURI), aURISpec, mCurrentCharset.get());
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsCOMPtr<nsIURL> url(do_QueryInterface(docURI, &rv));
+    nsAutoCString extension;
+    if (NS_SUCCEEDED(rv)) {
+      url->GetFileExtension(extension);
+    } else {
+      extension.AssignLiteral("htm");
+    }
+    aData->mSubFrameExt.Assign(char16_t('.'));
+    AppendUTF8toUTF16(extension, aData->mSubFrameExt);
+  } else {
+    aData->mSubFrameExt.Assign(char16_t('.'));
+    aData->mSubFrameExt.Append(ext);
+  }
+
+  nsString filenameWithExt = aData->mFilename;
+  filenameWithExt.Append(aData->mSubFrameExt);
+
+  // Work out the path for the subframe
+  nsCOMPtr<nsIURI> frameURI = mCurrentDataPath;
+  rv = AppendPathToURI(frameURI, filenameWithExt, frameURI);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Work out the path for the subframe data
+  nsCOMPtr<nsIURI> frameDataURI = mCurrentDataPath;
+  nsAutoString newFrameDataPath(aData->mFilename);
+
+  // Append _data
+  newFrameDataPath.AppendLiteral("_data");
+  rv = AppendPathToURI(frameDataURI, newFrameDataPath, frameDataURI);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Make frame document & data path conformant and unique
+  nsCOMPtr<nsIURI> out;
+  rv = CalculateUniqueFilename(frameURI, out);
+  NS_ENSURE_SUCCESS(rv, rv);
+  frameURI = out;
+
+  rv = CalculateUniqueFilename(frameDataURI, out);
+  NS_ENSURE_SUCCESS(rv, rv);
+  frameDataURI = out;
+
+  mCurrentThingsToPersist++;
+
+  // We shouldn't use SaveDocumentInternal for the contents
+  // of frames that are not documents, e.g. images.
+  if (DocumentEncoderExists(contentType.get())) {
+    auto toWalk = mozilla::MakeUnique<WalkData>();
+    toWalk->mDocument = aFrameContent;
+    toWalk->mFile = frameURI;
+    toWalk->mDataPath = frameDataURI;
+    mWalkStack.AppendElement(std::move(toWalk));
+  } else {
+    nsContentPolicyType policyType = nsIContentPolicy::TYPE_OTHER;
+    if (StringBeginsWith(contentType, "image/"_ns)) {
+      policyType = nsIContentPolicy::TYPE_IMAGE;
+    } else if (StringBeginsWith(contentType, "audio/"_ns) ||
+               StringBeginsWith(contentType, "video/"_ns)) {
+      policyType = nsIContentPolicy::TYPE_MEDIA;
+    }
+    rv = StoreURI(aURISpec, aParentDocument, policyType);
+  }
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Store the updated uri to the frame
+  aData->mFile = frameURI;
+  aData->mSubFrameExt.Truncate();  // we already put this in frameURI
+
+  return NS_OK;
+}
+
+nsresult nsWebBrowserPersist::CreateChannelFromURI(nsIURI* aURI,
+                                                   nsIChannel** aChannel) {
+  nsresult rv = NS_OK;
+  *aChannel = nullptr;
+
+  rv = NS_NewChannel(aChannel, aURI, nsContentUtils::GetSystemPrincipal(),
+                     nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_SEC_CONTEXT_IS_NULL,
+                     nsIContentPolicy::TYPE_OTHER);
+  NS_ENSURE_SUCCESS(rv, rv);
+  NS_ENSURE_ARG_POINTER(*aChannel);
+
+  rv = (*aChannel)->SetNotificationCallbacks(
+      static_cast<nsIInterfaceRequestor*>(this));
+  NS_ENSURE_SUCCESS(rv, rv);
+  return NS_OK;
+}
+
+// we store the current location as the key (absolutized version of domnode's
+// attribute's value)
+nsresult nsWebBrowserPersist::MakeAndStoreLocalFilenameInURIMap(
+    nsIURI* aURI, nsIWebBrowserPersistDocument* aDoc,
+    nsContentPolicyType aContentPolicyType, bool aNeedsPersisting,
+    URIData** aData) {
+  NS_ENSURE_ARG_POINTER(aURI);
+
+  nsAutoCString spec;
+  nsresult rv = aURI->GetSpec(spec);
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+
+  // Create a sensibly named filename for the URI and store in the URI map
+  URIData* data;
+  if (mURIMap.Get(spec, &data)) {
+    if (aNeedsPersisting) {
+      data->mNeedsPersisting = true;
+    }
+    if (aData) {
+      *aData = data;
+    }
+    return NS_OK;
+  }
+
+  // Create a unique file name for the uri
+  nsString filename;
+  rv = MakeFilenameFromURI(aURI, filename);
+  NS_ENSURE_SUCCESS(rv, NS_ERROR_FAILURE);
+
+  // Store the file name
+  data = new URIData;
+
+  data->mContentPolicyType = aContentPolicyType;
+  data->mNeedsPersisting = aNeedsPersisting;
+  data->mNeedsFixup = true;
+  data->mFilename = filename;
+  data->mSaved = false;
+  data->mIsSubFrame = false;
+  data->mDataPath = mCurrentDataPath;
+  data->mDataPathIsRelative = mCurrentDataPathIsRelative;
+  data->mRelativePathToData = mCurrentRelativePathToData;
+  data->mRelativeDocumentURI = mTargetBaseURI;
+  data->mCharset = mCurrentCharset;
+
+  aDoc->GetPrincipal(getter_AddRefs(data->mTriggeringPrincipal));
+  aDoc->GetCookieJarSettings(getter_AddRefs(data->mCookieJarSettings));
+
+  if (aNeedsPersisting) mCurrentThingsToPersist++;
+
+  mURIMap.InsertOrUpdate(spec, UniquePtr<URIData>(data));
+  if (aData) {
+    *aData = data;
+  }
+
+  return NS_OK;
+}
+
+// Decide if we need to apply conversion to the passed channel.
+void nsWebBrowserPersist::SetApplyConversionIfNeeded(nsIChannel* aChannel) {
+  nsresult rv = NS_OK;
+  nsCOMPtr<nsIEncodedChannel> encChannel = do_QueryInterface(aChannel, &rv);
+  if (NS_FAILED(rv)) return;
+
+  // Set the default conversion preference:
+  encChannel->SetApplyConversion(false);
+
+  nsCOMPtr<nsIURI> thisURI;
+  aChannel->GetURI(getter_AddRefs(thisURI));
+  nsCOMPtr<nsIURL> sourceURL(do_QueryInterface(thisURI));
+  if (!sourceURL) return;
+  nsAutoCString extension;
+  sourceURL->GetFileExtension(extension);
+
+  nsCOMPtr<nsIUTF8StringEnumerator> encEnum;
+  encChannel->GetContentEncodings(getter_AddRefs(encEnum));
+  if (!encEnum) return;
+  nsCOMPtr<nsIExternalHelperAppService> helperAppService =
+      do_GetService(NS_EXTERNALHELPERAPPSERVICE_CONTRACTID, &rv);
+  if (NS_FAILED(rv)) return;
+  bool hasMore;
+  rv = encEnum->HasMore(&hasMore);
+  if (NS_SUCCEEDED(rv) && hasMore) {
+    nsAutoCString encType;
+    rv = encEnum->GetNext(encType);
+    if (NS_SUCCEEDED(rv)) {
+      bool applyConversion = false;
+      rv = helperAppService->ApplyDecodingForExtension(extension, encType,
+                                                       &applyConversion);
+      if (NS_SUCCEEDED(rv)) encChannel->SetApplyConversion(applyConversion);
+    }
+  }
+}
diff --git a/dom/webbrowserpersist/nsWebBrowserPersist.h b/dom/webbrowserpersist/nsWebBrowserPersist.h
new file mode 100644
index 0000000000..47f13b1cb4
--- /dev/null
+++ b/dom/webbrowserpersist/nsWebBrowserPersist.h
@@ -0,0 +1,191 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * 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 nsWebBrowserPersist_h__
+#define nsWebBrowserPersist_h__
+
+#include "nsCOMPtr.h"
+#include "nsWeakReference.h"
+
+#include "nsIInterfaceRequestor.h"
+#include "nsIMIMEService.h"
+#include "nsIStreamListener.h"
+#include "nsIOutputStream.h"
+#include "nsIInputStream.h"
+#include "nsIChannel.h"
+#include "nsIProgressEventSink.h"
+#include "nsIFile.h"
+#include "nsIThreadRetargetableStreamListener.h"
+#include "nsIWebProgressListener2.h"
+#include "nsIWebBrowserPersist.h"
+#include "nsIWebBrowserPersistDocument.h"
+
+#include "mozilla/MozPromise.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/UniquePtr.h"
+#include "nsClassHashtable.h"
+#include "nsHashKeys.h"
+#include "nsTArray.h"
+
+class nsIStorageStream;
+class nsIWebBrowserPersistDocument;
+
+using ClosePromise = mozilla::MozPromise<nsresult, nsresult, true>;
+
+class nsWebBrowserPersist final : public nsIInterfaceRequestor,
+                                  public nsIWebBrowserPersist,
+                                  public nsIStreamListener,
+                                  public nsIThreadRetargetableStreamListener,
+                                  public nsIProgressEventSink,
+                                  public nsSupportsWeakReference {
+  friend class nsEncoderNodeFixup;
+
+  // Public members
+ public:
+  nsWebBrowserPersist();
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIINTERFACEREQUESTOR
+  NS_DECL_NSICANCELABLE
+  NS_DECL_NSIWEBBROWSERPERSIST
+  NS_DECL_NSIREQUESTOBSERVER
+  NS_DECL_NSISTREAMLISTENER
+  NS_DECL_NSITHREADRETARGETABLESTREAMLISTENER
+  NS_DECL_NSIPROGRESSEVENTSINK
+
+  // Private members
+ private:
+  virtual ~nsWebBrowserPersist();
+  nsresult SaveURIInternal(nsIURI* aURI, nsIPrincipal* aTriggeringPrincipal,
+                           nsContentPolicyType aContentPolicyType,
+                           uint32_t aCacheKey, nsIReferrerInfo* aReferrerInfo,
+                           nsICookieJarSettings* aCookieJarSettings,
+                           nsIInputStream* aPostData, const char* aExtraHeaders,
+                           nsIURI* aFile, bool aCalcFileExt, bool aIsPrivate);
+  nsresult SaveChannelInternal(nsIChannel* aChannel, nsIURI* aFile,
+                               bool aCalcFileExt);
+  nsresult SaveDocumentInternal(nsIWebBrowserPersistDocument* aDocument,
+                                nsIURI* aFile, nsIURI* aDataPath);
+  nsresult SaveDocuments();
+  void FinishSaveDocumentInternal(nsIURI* aFile, nsIFile* aDataPath);
+  nsresult GetExtensionForContentType(const char16_t* aContentType,
+                                      char16_t** aExt);
+
+  struct CleanupData;
+  struct DocData;
+  struct OutputData;
+  struct UploadData;
+  struct URIData;
+  struct WalkData;
+
+  class OnWalk;
+  class OnRemoteWalk;
+  class OnWrite;
+  class FlatURIMap;
+  friend class OnWalk;
+  friend class OnWrite;
+
+  nsresult SaveDocumentDeferred(mozilla::UniquePtr<WalkData>&& aData);
+  void Cleanup();
+  void CleanupLocalFiles();
+  nsresult GetValidURIFromObject(nsISupports* aObject, nsIURI** aURI) const;
+  static nsresult GetLocalFileFromURI(nsIURI* aURI, nsIFile** aLocalFile);
+  static nsresult AppendPathToURI(nsIURI* aURI, const nsAString& aPath,
+                                  nsCOMPtr<nsIURI>& aOutURI);
+  nsresult MakeAndStoreLocalFilenameInURIMap(
+      nsIURI* aURI, nsIWebBrowserPersistDocument* aDoc,
+      nsContentPolicyType aContentPolicyType, bool aNeedsPersisting,
+      URIData** aData);
+  nsresult MakeOutputStream(nsIURI* aFile, nsIOutputStream** aOutputStream);
+  nsresult MakeOutputStreamFromFile(nsIFile* aFile,
+                                    nsIOutputStream** aOutputStream);
+  nsresult MakeOutputStreamFromURI(nsIURI* aURI, nsIOutputStream** aOutStream);
+  nsresult CreateChannelFromURI(nsIURI* aURI, nsIChannel** aChannel);
+  nsresult StartUpload(nsIStorageStream* aOutStream, nsIURI* aDestinationURI,
+                       const nsACString& aContentType);
+  nsresult StartUpload(nsIInputStream* aInputStream, nsIURI* aDestinationURI,
+                       const nsACString& aContentType);
+  nsresult CalculateAndAppendFileExt(nsIURI* aURI, nsIChannel* aChannel,
+                                     nsIURI* aOriginalURIWithExtension,
+                                     nsCOMPtr<nsIURI>& aOutURI);
+  nsresult CalculateUniqueFilename(nsIURI* aURI, nsCOMPtr<nsIURI>& aOutURI);
+  nsresult MakeFilenameFromURI(nsIURI* aURI, nsString& aFilename);
+  nsresult StoreURI(const nsACString& aURI, nsIWebBrowserPersistDocument* aDoc,
+                    nsContentPolicyType aContentPolicyType,
+                    bool aNeedsPersisting = true, URIData** aData = nullptr);
+  nsresult StoreURI(nsIURI* aURI, nsIWebBrowserPersistDocument* aDoc,
+                    nsContentPolicyType aContentPolicyType,
+                    bool aNeedsPersisting = true, URIData** aData = nullptr);
+  bool DocumentEncoderExists(const char* aContentType);
+
+  nsresult SaveSubframeContent(nsIWebBrowserPersistDocument* aFrameContent,
+                               nsIWebBrowserPersistDocument* aParentDocument,
+                               const nsCString& aURISpec, URIData* aData);
+  nsresult SendErrorStatusChange(bool aIsReadError, nsresult aResult,
+                                 nsIRequest* aRequest, nsIURI* aURI);
+
+  nsresult FixRedirectedChannelEntry(nsIChannel* aNewChannel);
+
+  void FinishDownload();
+  void EndDownload(nsresult aResult);
+  void EndDownloadInternal(nsresult aResult);
+  void SerializeNextFile();
+  void CalcTotalProgress();
+
+  void SetApplyConversionIfNeeded(nsIChannel* aChannel);
+
+  nsCOMPtr<nsIURI> mCurrentDataPath;
+  bool mCurrentDataPathIsRelative;
+  nsCString mCurrentRelativePathToData;
+  nsCOMPtr<nsIURI> mCurrentBaseURI;
+  nsCString mCurrentCharset;
+  nsCOMPtr<nsIURI> mTargetBaseURI;
+  uint32_t mCurrentThingsToPersist;
+
+  nsCOMPtr<nsIMIMEService> mMIMEService;
+  nsCOMPtr<nsIURI> mURI;
+  nsCOMPtr<nsIWebProgressListener> mProgressListener;
+  /**
+   * Progress listener for 64-bit values; this is the same object as
+   * mProgressListener, but is a member to avoid having to qi it for each
+   * progress notification.
+   */
+  nsCOMPtr<nsIWebProgressListener2> mProgressListener2;
+  nsCOMPtr<nsIProgressEventSink> mEventSink;
+  mozilla::Mutex mOutputMapMutex MOZ_UNANNOTATED;
+  nsClassHashtable<nsISupportsHashKey, OutputData> mOutputMap;
+  nsClassHashtable<nsISupportsHashKey, UploadData> mUploadList;
+  nsCOMPtr<nsISerialEventTarget> mBackgroundQueue;
+  nsTArray<RefPtr<ClosePromise>> mFileClosePromises;
+  nsClassHashtable<nsCStringHashKey, URIData> mURIMap;
+  nsCOMPtr<nsIWebBrowserPersistURIMap> mFlatURIMap;
+  nsTArray<mozilla::UniquePtr<WalkData>> mWalkStack;
+  nsTArray<DocData*> mDocList;
+  nsTArray<CleanupData*> mCleanupList;
+  nsTArray<nsCString> mFilenameList;
+  bool mFirstAndOnlyUse;
+  bool mSavingDocument;
+  // mCancel is used from both the main thread, and (inside OnDataAvailable)
+  // from a background thread.
+  mozilla::Atomic<bool> mCancel;
+  bool mEndCalled;
+  bool mCompleted;
+  bool mStartSaving;
+  bool mReplaceExisting;
+  bool mSerializingOutput;
+  bool mIsPrivate;
+  // mPersistFlags can be modified on the main thread, and can be read from
+  // a background thread when OnDataAvailable calls MakeOutputStreamFromFile.
+  mozilla::Atomic<uint32_t> mPersistFlags;
+  nsresult mPersistResult;
+  int64_t mTotalCurrentProgress;
+  int64_t mTotalMaxProgress;
+  int16_t mWrapColumn;
+  uint32_t mEncodingFlags;
+  nsString mContentType;
+};
+
+#endif