Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

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

1 files changed, 3925 insertions, 0 deletions

diff --git a/dom/base/nsFrameLoader.cpp b/dom/base/nsFrameLoader.cpp
new file mode 100644
index 0000000000..0b809adece
--- /dev/null
+++ b/dom/base/nsFrameLoader.cpp
@@ -0,0 +1,3925 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * Class for managing loading of a subframe (creation of the docshell,
+ * handling of loads in it, recursion-checking).
+ */
+
+#include "nsFrameLoader.h"
+
+#include "base/basictypes.h"
+
+#include "prenv.h"
+
+#include "nsDocShell.h"
+#include "nsIContentInlines.h"
+#include "nsIContentViewer.h"
+#include "nsIPrintSettings.h"
+#include "nsIPrintSettingsService.h"
+#include "mozilla/dom/Document.h"
+#include "nsPIDOMWindow.h"
+#include "nsIWebNavigation.h"
+#include "nsIWebProgress.h"
+#include "nsIDocShell.h"
+#include "nsIDocShellTreeOwner.h"
+#include "nsDocShellLoadState.h"
+#include "nsIBaseWindow.h"
+#include "nsIBrowser.h"
+#include "nsContentUtils.h"
+#include "nsUnicharUtils.h"
+#include "nsIScriptGlobalObject.h"
+#include "nsIScriptSecurityManager.h"
+#include "nsFrameLoaderOwner.h"
+#include "nsIFrame.h"
+#include "nsIScrollableFrame.h"
+#include "nsSubDocumentFrame.h"
+#include "nsError.h"
+#include "nsIAppWindow.h"
+#include "nsIMozBrowserFrame.h"
+#include "nsIScriptError.h"
+#include "nsGlobalWindow.h"
+#include "nsHTMLDocument.h"
+#include "nsPIWindowRoot.h"
+#include "nsLayoutUtils.h"
+#include "nsMappedAttributes.h"
+#include "nsView.h"
+#include "nsBaseWidget.h"
+#include "nsQueryObject.h"
+#include "ReferrerInfo.h"
+#include "nsIOpenWindowInfo.h"
+#include "nsISHistory.h"
+#include "nsIURI.h"
+#include "nsIXULRuntime.h"
+#include "nsNetUtil.h"
+#include "nsFocusManager.h"
+#include "nsIINIParser.h"
+#include "nsAppRunner.h"
+#include "nsDirectoryService.h"
+#include "nsDirectoryServiceDefs.h"
+
+#include "nsGkAtoms.h"
+#include "nsNameSpaceManager.h"
+
+#include "nsThreadUtils.h"
+
+#include "nsIDOMChromeWindow.h"
+#include "InProcessBrowserChildMessageManager.h"
+
+#include "ContentParent.h"
+#include "BrowserParent.h"
+#include "mozilla/AsyncEventDispatcher.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/ExpandedPrincipal.h"
+#include "mozilla/FlushType.h"
+#include "mozilla/HTMLEditor.h"
+#include "mozilla/NullPrincipal.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/PresShellInlines.h"
+#include "mozilla/ProcessPriorityManager.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/StaticPrefs_fission.h"
+#include "mozilla/Unused.h"
+#include "mozilla/dom/BrowsingContext.h"
+#include "mozilla/dom/ChromeMessageSender.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/FrameCrashedEvent.h"
+#include "mozilla/dom/FrameLoaderBinding.h"
+#include "mozilla/dom/InProcessChild.h"
+#include "mozilla/dom/MozFrameLoaderOwnerBinding.h"
+#include "mozilla/dom/PBrowser.h"
+#include "mozilla/dom/SessionHistoryEntry.h"
+#include "mozilla/dom/SessionStoreChild.h"
+#include "mozilla/dom/SessionStoreParent.h"
+#include "mozilla/dom/SessionStoreUtils.h"
+#include "mozilla/dom/WindowGlobalParent.h"
+#include "mozilla/dom/XULFrameElement.h"
+#include "mozilla/gfx/CrossProcessPaint.h"
+#include "mozilla/ProfilerLabels.h"
+#include "nsGenericHTMLFrameElement.h"
+
+#include "jsapi.h"
+#include "mozilla/dom/HTMLIFrameElement.h"
+#include "nsSandboxFlags.h"
+#include "mozilla/layers/CompositorBridgeChild.h"
+#include "mozilla/dom/CustomEvent.h"
+
+#include "mozilla/dom/ipc/StructuredCloneData.h"
+#include "mozilla/WebBrowserPersistLocalDocument.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/PromiseNativeHandler.h"
+#include "mozilla/dom/ChildSHistory.h"
+#include "mozilla/dom/CanonicalBrowsingContext.h"
+#include "mozilla/dom/ContentChild.h"
+#include "mozilla/dom/ContentProcessManager.h"
+#include "mozilla/dom/BrowserBridgeChild.h"
+#include "mozilla/dom/BrowserHost.h"
+#include "mozilla/dom/BrowserBridgeHost.h"
+#include "mozilla/dom/BrowsingContextGroup.h"
+
+#include "mozilla/dom/SessionStorageManager.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/dom/PBackgroundSessionStorageCache.h"
+#include "mozilla/ipc/BackgroundUtils.h"
+
+#include "mozilla/dom/HTMLBodyElement.h"
+
+#include "mozilla/ContentPrincipal.h"
+
+#include "nsXULPopupManager.h"
+
+#ifdef NS_PRINTING
+#  include "nsIWebBrowserPrint.h"
+#endif
+
+#if defined(MOZ_TELEMETRY_REPORTING)
+#  include "mozilla/Telemetry.h"
+#endif  // defined(MOZ_TELEMETRY_REPORTING)
+
+using namespace mozilla;
+using namespace mozilla::hal;
+using namespace mozilla::dom;
+using namespace mozilla::dom::ipc;
+using namespace mozilla::ipc;
+using namespace mozilla::layers;
+using namespace mozilla::layout;
+using ViewID = ScrollableLayerGuid::ViewID;
+
+using PrintPreviewResolver = std::function<void(const PrintPreviewResultInfo&)>;
+
+// Bug 8065: Limit content frame depth to some reasonable level. This
+// does not count chrome frames when determining depth, nor does it
+// prevent chrome recursion.  Number is fairly arbitrary, but meant to
+// keep number of shells to a reasonable number on accidental recursion with a
+// small (but not 1) branching factor.  With large branching factors the number
+// of shells can rapidly become huge and run us out of memory.  To solve that,
+// we'd need to re-institute a fixed version of bug 98158.
+#define MAX_DEPTH_CONTENT_FRAMES 10
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(nsFrameLoader, mPendingBrowsingContext,
+                                      mMessageManager, mChildMessageManager,
+                                      mRemoteBrowser, mSessionStoreChild)
+NS_IMPL_CYCLE_COLLECTING_ADDREF(nsFrameLoader)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(nsFrameLoader)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsFrameLoader)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY_CONCRETE(nsFrameLoader)
+  NS_INTERFACE_MAP_ENTRY(nsIMutationObserver)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+nsFrameLoader::nsFrameLoader(Element* aOwner, BrowsingContext* aBrowsingContext,
+                             bool aIsRemoteFrame, bool aNetworkCreated)
+    : mPendingBrowsingContext(aBrowsingContext),
+      mOwnerContent(aOwner),
+      mDetachedSubdocFrame(nullptr),
+      mPendingSwitchID(0),
+      mChildID(0),
+      mRemoteType(NOT_REMOTE_TYPE),
+      mInitialized(false),
+      mDepthTooGreat(false),
+      mIsTopLevelContent(false),
+      mDestroyCalled(false),
+      mNeedsAsyncDestroy(false),
+      mInSwap(false),
+      mInShow(false),
+      mHideCalled(false),
+      mNetworkCreated(aNetworkCreated),
+      mLoadingOriginalSrc(false),
+      mRemoteBrowserShown(false),
+      mIsRemoteFrame(aIsRemoteFrame),
+      mWillChangeProcess(false),
+      mObservingOwnerContent(false),
+      mTabProcessCrashFired(false) {
+  nsCOMPtr<nsFrameLoaderOwner> owner = do_QueryInterface(aOwner);
+  owner->AttachFrameLoader(this);
+}
+
+nsFrameLoader::~nsFrameLoader() {
+  if (mMessageManager) {
+    mMessageManager->Disconnect();
+  }
+
+  MOZ_ASSERT(!mOwnerContent);
+  MOZ_RELEASE_ASSERT(mDestroyCalled);
+}
+
+static nsAtom* TypeAttrName(Element* aOwnerContent) {
+  return aOwnerContent->IsXULElement() ? nsGkAtoms::type
+                                       : nsGkAtoms::mozframetype;
+}
+
+static void GetFrameName(Element* aOwnerContent, nsAString& aFrameName) {
+  int32_t namespaceID = aOwnerContent->GetNameSpaceID();
+  if (namespaceID == kNameSpaceID_XHTML && !aOwnerContent->IsInHTMLDocument()) {
+    aOwnerContent->GetAttr(kNameSpaceID_None, nsGkAtoms::id, aFrameName);
+  } else {
+    aOwnerContent->GetAttr(kNameSpaceID_None, nsGkAtoms::name, aFrameName);
+    // XXX if no NAME then use ID, after a transition period this will be
+    // changed so that XUL only uses ID too (bug 254284).
+    if (aFrameName.IsEmpty() && namespaceID == kNameSpaceID_XUL) {
+      aOwnerContent->GetAttr(kNameSpaceID_None, nsGkAtoms::id, aFrameName);
+    }
+  }
+}
+
+// If this method returns true, the nsFrameLoader will act as a boundary, as is
+// the case for <iframe mozbrowser> and <browser type="content"> elements.
+//
+// # Historical Notes  (10 April 2019)
+//
+// In the past, this boundary was defined by the "typeContent" and "typeChrome"
+// nsIDocShellTreeItem types. There was only ever a single split in the tree,
+// and it occurred at the boundary between these two types of docshells. When
+// <iframe mozbrowser> was introduced, it was given special casing to make it
+// act like a second boundary, without having to change the existing code.
+//
+// The about:addons page, which is loaded within a content browser, then added a
+// remote <browser type="content" remote="true"> element. When remote, this
+// would also act as a mechanism for creating a disjoint tree, due to the
+// process keeping the embedder and embedee separate.
+//
+// However, when initial out-of-process iframe support was implemented, this
+// codepath became a risk, as it could've caused the oop iframe remote
+// WindowProxy code to be activated for the addons page. This was fixed by
+// extendng the isolation logic previously reserved to <iframe mozbrowser> to
+// also cover <browser> elements with the explicit `remote` property loaded in
+// content.
+//
+// To keep these boundaries clear, and allow them to work in a cross-process
+// manner, they are no longer handled by typeContent and typeChrome. Instead,
+// the actual BrowsingContext tree is broken at these edges.
+static bool IsTopContent(BrowsingContext* aParent, Element* aOwner) {
+  if (XRE_IsContentProcess()) {
+    return false;
+  }
+
+  // If we have a (deprecated) mozbrowser element, we want to start a new
+  // BrowsingContext tree regardless of whether the parent is chrome or content.
+  nsCOMPtr<nsIMozBrowserFrame> mozbrowser = aOwner->GetAsMozBrowserFrame();
+  if (mozbrowser && mozbrowser->GetReallyIsBrowser()) {
+    return true;
+  }
+
+  if (aParent->IsContent()) {
+    // If we're already in content, we may still want to create a new
+    // BrowsingContext tree if our element is a xul browser element with a
+    // `remote="true"` marker.
+    return aOwner->IsXULElement() &&
+           aOwner->AttrValueIs(kNameSpaceID_None, nsGkAtoms::remote,
+                               nsGkAtoms::_true, eCaseMatters);
+  }
+
+  // If we're in a chrome context, we want to start a new tree if we are an
+  // element with a `type="content"` marker.
+  return aOwner->AttrValueIs(kNameSpaceID_None, TypeAttrName(aOwner),
+                             nsGkAtoms::content, eIgnoreCase);
+}
+
+static already_AddRefed<BrowsingContext> CreateBrowsingContext(
+    Element* aOwner, nsIOpenWindowInfo* aOpenWindowInfo,
+    BrowsingContextGroup* aSpecificGroup, bool aNetworkCreated = false) {
+  MOZ_ASSERT(!aOpenWindowInfo || !aSpecificGroup,
+             "Only one of SpecificGroup and OpenWindowInfo may be provided!");
+
+  // If we've got a pending BrowserParent from the content process, use the
+  // BrowsingContext which was created for it.
+  if (aOpenWindowInfo && aOpenWindowInfo->GetNextRemoteBrowser()) {
+    MOZ_ASSERT(XRE_IsParentProcess());
+    return do_AddRef(
+        aOpenWindowInfo->GetNextRemoteBrowser()->GetBrowsingContext());
+  }
+
+  RefPtr<BrowsingContext> opener;
+  if (aOpenWindowInfo && !aOpenWindowInfo->GetForceNoOpener()) {
+    opener = aOpenWindowInfo->GetParent();
+    if (opener) {
+      // Must create BrowsingContext with opener in-process.
+      MOZ_ASSERT(opener->IsInProcess());
+
+      // This can only happen when the opener was closed from a nested event
+      // loop in the window provider code, and only when the open was triggered
+      // by a non-e10s tab, and the new tab is being opened in a new browser
+      // window. Since it is a corner case among corner cases, and the opener
+      // window will appear to be null to consumers after it is discarded
+      // anyway, just drop the opener entirely.
+      if (opener->IsDiscarded()) {
+        NS_WARNING(
+            "Opener was closed from a nested event loop in the parent process. "
+            "Please fix this.");
+        opener = nullptr;
+      }
+    }
+  }
+
+  RefPtr<nsGlobalWindowInner> parentInner =
+      nsGlobalWindowInner::Cast(aOwner->OwnerDoc()->GetInnerWindow());
+  if (NS_WARN_IF(!parentInner) || parentInner->IsDying()) {
+    return nullptr;
+  }
+
+  BrowsingContext* parentBC = parentInner->GetBrowsingContext();
+  if (NS_WARN_IF(!parentBC) || parentBC->IsDiscarded()) {
+    return nullptr;
+  }
+
+  // Determine the frame name for the new browsing context.
+  nsAutoString frameName;
+  GetFrameName(aOwner, frameName);
+
+  // Create our BrowsingContext without immediately attaching it. It's possible
+  // that no DocShell or remote browser will ever be created for this
+  // FrameLoader, particularly if the document that we were created for is not
+  // currently active. And in that latter case, if we try to attach our BC now,
+  // it will wind up attached as a child of the currently active inner window
+  // for the BrowsingContext, and cause no end of trouble.
+  if (IsTopContent(parentBC, aOwner)) {
+    // Create toplevel context without a parent & as Type::Content.
+    return BrowsingContext::CreateDetached(
+        nullptr, opener, aSpecificGroup, frameName,
+        BrowsingContext::Type::Content, false);
+  }
+
+  MOZ_ASSERT(!aOpenWindowInfo,
+             "Can't have openWindowInfo for non-toplevel context");
+
+  MOZ_ASSERT(!aSpecificGroup,
+             "Can't force BrowsingContextGroup for non-toplevel context");
+  return BrowsingContext::CreateDetached(parentInner, nullptr, nullptr,
+                                         frameName, parentBC->GetType(), false,
+                                         !aNetworkCreated);
+}
+
+static bool InitialLoadIsRemote(Element* aOwner) {
+  if (PR_GetEnv("MOZ_DISABLE_OOP_TABS") ||
+      Preferences::GetBool("dom.ipc.tabs.disabled", false)) {
+    return false;
+  }
+
+  // The initial load in an content process iframe should never be made remote.
+  // Content process iframes always become remote due to navigation.
+  if (XRE_IsContentProcess()) {
+    return false;
+  }
+
+  // If we're an <iframe mozbrowser> and we don't have a "remote" attribute,
+  // fall back to the default.
+  nsCOMPtr<nsIMozBrowserFrame> browserFrame = do_QueryInterface(aOwner);
+  bool isMozBrowserFrame = browserFrame && browserFrame->GetReallyIsBrowser();
+  if (isMozBrowserFrame &&
+      !aOwner->HasAttr(kNameSpaceID_None, nsGkAtoms::remote)) {
+    return Preferences::GetBool("dom.ipc.browser_frames.oop_by_default", false);
+  }
+
+  // Otherwise, we're remote if we have "remote=true" and we're either a
+  // browser frame or a XUL element.
+  return (isMozBrowserFrame || aOwner->GetNameSpaceID() == kNameSpaceID_XUL) &&
+         aOwner->AttrValueIs(kNameSpaceID_None, nsGkAtoms::remote,
+                             nsGkAtoms::_true, eCaseMatters);
+}
+
+static already_AddRefed<BrowsingContextGroup> InitialBrowsingContextGroup(
+    Element* aOwner) {
+  nsAutoString attrString;
+  if (aOwner->GetNameSpaceID() != kNameSpaceID_XUL ||
+      !aOwner->GetAttr(nsGkAtoms::initialBrowsingContextGroupId, attrString)) {
+    return nullptr;
+  }
+
+  // It's OK to read the attribute using a signed 64-bit integer parse, as an ID
+  // generated using `nsContentUtils::GenerateProcessSpecificId` (like BCG IDs)
+  // will only ever use 53 bits of precision, so it can be round-tripped through
+  // a JS number.
+  nsresult rv = NS_OK;
+  int64_t signedGroupId = attrString.ToInteger64(&rv, 10);
+  if (NS_FAILED(rv) || signedGroupId <= 0) {
+    MOZ_DIAGNOSTIC_ASSERT(
+        false, "we intended to have a particular id, but failed to parse it!");
+    return nullptr;
+  }
+
+  return BrowsingContextGroup::GetOrCreate(uint64_t(signedGroupId));
+}
+
+already_AddRefed<nsFrameLoader> nsFrameLoader::Create(
+    Element* aOwner, bool aNetworkCreated, nsIOpenWindowInfo* aOpenWindowInfo) {
+  NS_ENSURE_TRUE(aOwner, nullptr);
+  Document* doc = aOwner->OwnerDoc();
+
+  // We never create nsFrameLoaders for elements in resource documents.
+  //
+  // We never create nsFrameLoaders for elements in data documents, unless the
+  // document is a static document.
+  // Static documents are an exception because any sub-documents need an
+  // nsFrameLoader to keep the relevant docShell alive, even though the
+  // nsFrameLoader isn't used to load anything (the sub-document is created by
+  // the static clone process).
+  //
+  // We never create nsFrameLoaders for elements that are not
+  // in-composed-document, unless the element belongs to a static document.
+  // Static documents are an exception because this method is called at a point
+  // in the static clone process before aOwner has been inserted into its
+  // document.  For other types of documents this wouldn't be a problem since
+  // we'd create the nsFrameLoader as necessary after aOwner is inserted into a
+  // document, but the mechanisms that take care of that don't apply for static
+  // documents so we need to create the nsFrameLoader now. (This isn't wasteful
+  // since for a static document we know aOwner will end up in a document and
+  // the nsFrameLoader will be used for its docShell.)
+  //
+  NS_ENSURE_TRUE(!doc->IsResourceDoc() &&
+                     ((!doc->IsLoadedAsData() && aOwner->IsInComposedDoc()) ||
+                      doc->IsStaticDocument()),
+                 nullptr);
+
+  RefPtr<BrowsingContextGroup> group = InitialBrowsingContextGroup(aOwner);
+  RefPtr<BrowsingContext> context =
+      CreateBrowsingContext(aOwner, aOpenWindowInfo, group, aNetworkCreated);
+  NS_ENSURE_TRUE(context, nullptr);
+
+  if (XRE_IsParentProcess() && aOpenWindowInfo) {
+    MOZ_ASSERT(context->IsTopContent());
+    if (RefPtr<BrowsingContext> crossGroupOpener =
+            aOpenWindowInfo->GetParent()) {
+      context->Canonical()->SetCrossGroupOpenerId(crossGroupOpener->Id());
+    }
+  }
+
+  bool isRemoteFrame = InitialLoadIsRemote(aOwner);
+  RefPtr<nsFrameLoader> fl =
+      new nsFrameLoader(aOwner, context, isRemoteFrame, aNetworkCreated);
+  fl->mOpenWindowInfo = aOpenWindowInfo;
+
+  // If this is a toplevel initial remote frame, we're looking at a browser
+  // loaded in the parent process. Pull the remote type attribute off of the
+  // <browser> element to determine which remote type it should be loaded in, or
+  // use `DEFAULT_REMOTE_TYPE` if we can't tell.
+  if (isRemoteFrame) {
+    MOZ_ASSERT(XRE_IsParentProcess());
+    nsAutoString remoteType;
+    if (aOwner->GetAttr(kNameSpaceID_None, nsGkAtoms::RemoteType, remoteType) &&
+        !remoteType.IsEmpty()) {
+      CopyUTF16toUTF8(remoteType, fl->mRemoteType);
+    } else {
+      fl->mRemoteType = DEFAULT_REMOTE_TYPE;
+    }
+  }
+  return fl.forget();
+}
+
+/* static */
+already_AddRefed<nsFrameLoader> nsFrameLoader::Recreate(
+    mozilla::dom::Element* aOwner, BrowsingContext* aContext,
+    BrowsingContextGroup* aSpecificGroup,
+    const NavigationIsolationOptions& aRemotenessOptions, bool aIsRemote,
+    bool aNetworkCreated, bool aPreserveContext) {
+  NS_ENSURE_TRUE(aOwner, nullptr);
+
+#ifdef DEBUG
+  // This version of Create is only called for Remoteness updates, so we can
+  // assume we need a FrameLoader here and skip the check in the other Create.
+  Document* doc = aOwner->OwnerDoc();
+  MOZ_ASSERT(!doc->IsResourceDoc());
+  MOZ_ASSERT((!doc->IsLoadedAsData() && aOwner->IsInComposedDoc()) ||
+             doc->IsStaticDocument());
+#endif
+
+  RefPtr<BrowsingContext> context = aContext;
+  if (!context || !aPreserveContext) {
+    context = CreateBrowsingContext(aOwner, /* openWindowInfo */ nullptr,
+                                    aSpecificGroup);
+    if (aContext) {
+      MOZ_ASSERT(
+          XRE_IsParentProcess(),
+          "Recreating browing contexts only supported in the parent process");
+      aContext->Canonical()->SynchronizeLayoutHistoryState();
+      aContext->Canonical()->ReplacedBy(context->Canonical(),
+                                        aRemotenessOptions);
+    }
+  }
+  NS_ENSURE_TRUE(context, nullptr);
+
+  RefPtr<nsFrameLoader> fl =
+      new nsFrameLoader(aOwner, context, aIsRemote, aNetworkCreated);
+  return fl.forget();
+}
+
+void nsFrameLoader::LoadFrame(bool aOriginalSrc) {
+  if (NS_WARN_IF(!mOwnerContent)) {
+    return;
+  }
+
+  nsAutoString src;
+  nsCOMPtr<nsIPrincipal> principal;
+  nsCOMPtr<nsIContentSecurityPolicy> csp;
+
+  bool isSrcdoc = mOwnerContent->IsHTMLElement(nsGkAtoms::iframe) &&
+                  mOwnerContent->HasAttr(kNameSpaceID_None, nsGkAtoms::srcdoc);
+  if (isSrcdoc) {
+    src.AssignLiteral("about:srcdoc");
+    principal = mOwnerContent->NodePrincipal();
+    csp = mOwnerContent->GetCsp();
+  } else {
+    GetURL(src, getter_AddRefs(principal), getter_AddRefs(csp));
+
+    src.Trim(" \t\n\r");
+
+    if (src.IsEmpty()) {
+      // If the frame is a XUL element and has the attribute 'nodefaultsrc=true'
+      // then we will not use 'about:blank' as fallback but return early without
+      // starting a load if no 'src' attribute is given (or it's empty).
+      if (mOwnerContent->IsXULElement() &&
+          mOwnerContent->AttrValueIs(kNameSpaceID_None, nsGkAtoms::nodefaultsrc,
+                                     nsGkAtoms::_true, eCaseMatters)) {
+        return;
+      }
+      src.AssignLiteral("about:blank");
+      principal = mOwnerContent->NodePrincipal();
+      csp = mOwnerContent->GetCsp();
+    }
+  }
+
+  Document* doc = mOwnerContent->OwnerDoc();
+  if (doc->IsStaticDocument()) {
+    return;
+  }
+
+  nsIURI* base_uri = mOwnerContent->GetBaseURI();
+  auto encoding = doc->GetDocumentCharacterSet();
+
+  nsCOMPtr<nsIURI> uri;
+  nsresult rv = NS_NewURI(getter_AddRefs(uri), src, encoding, base_uri);
+
+  // If the URI was malformed, try to recover by loading about:blank.
+  if (rv == NS_ERROR_MALFORMED_URI) {
+    rv = NS_NewURI(getter_AddRefs(uri), u"about:blank"_ns, encoding, base_uri);
+  }
+
+  if (NS_SUCCEEDED(rv)) {
+    rv = LoadURI(uri, principal, csp, aOriginalSrc);
+  }
+
+  if (NS_FAILED(rv)) {
+    FireErrorEvent();
+  }
+}
+
+void nsFrameLoader::ConfigRemoteProcess(const nsACString& aRemoteType,
+                                        ContentParent* aContentParent) {
+  MOZ_DIAGNOSTIC_ASSERT(IsRemoteFrame(), "Must be a remote frame");
+  MOZ_DIAGNOSTIC_ASSERT(!mRemoteBrowser, "Must not have a browser yet");
+  MOZ_DIAGNOSTIC_ASSERT_IF(aContentParent,
+                           aContentParent->GetRemoteType() == aRemoteType);
+
+  mRemoteType = aRemoteType;
+  mChildID = aContentParent ? aContentParent->ChildID() : 0;
+}
+
+void nsFrameLoader::FireErrorEvent() {
+  if (!mOwnerContent) {
+    return;
+  }
+  RefPtr<AsyncEventDispatcher> loadBlockingAsyncDispatcher =
+      new LoadBlockingAsyncEventDispatcher(
+          mOwnerContent, u"error"_ns, CanBubble::eNo, ChromeOnlyDispatch::eNo);
+  loadBlockingAsyncDispatcher->PostDOMEvent();
+}
+
+nsresult nsFrameLoader::LoadURI(nsIURI* aURI,
+                                nsIPrincipal* aTriggeringPrincipal,
+                                nsIContentSecurityPolicy* aCsp,
+                                bool aOriginalSrc) {
+  if (!aURI) return NS_ERROR_INVALID_POINTER;
+  NS_ENSURE_STATE(!mDestroyCalled && mOwnerContent);
+  MOZ_ASSERT(
+      aTriggeringPrincipal,
+      "Must have an explicit triggeringPrincipal to nsFrameLoader::LoadURI.");
+
+  mLoadingOriginalSrc = aOriginalSrc;
+
+  nsCOMPtr<Document> doc = mOwnerContent->OwnerDoc();
+
+  nsresult rv;
+  rv = CheckURILoad(aURI, aTriggeringPrincipal);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  mURIToLoad = aURI;
+  mTriggeringPrincipal = aTriggeringPrincipal;
+  mCsp = aCsp;
+  rv = doc->InitializeFrameLoader(this);
+  if (NS_FAILED(rv)) {
+    mURIToLoad = nullptr;
+    mTriggeringPrincipal = nullptr;
+    mCsp = nullptr;
+  }
+  return rv;
+}
+
+void nsFrameLoader::ResumeLoad(uint64_t aPendingSwitchID) {
+  Document* doc = mOwnerContent->OwnerDoc();
+  if (doc->IsStaticDocument()) {
+    // Static doc shouldn't load sub-documents.
+    return;
+  }
+
+  if (NS_WARN_IF(mDestroyCalled || !mOwnerContent)) {
+    FireErrorEvent();
+    return;
+  }
+
+  mLoadingOriginalSrc = false;
+  mURIToLoad = nullptr;
+  mPendingSwitchID = aPendingSwitchID;
+  mTriggeringPrincipal = mOwnerContent->NodePrincipal();
+  mCsp = mOwnerContent->GetCsp();
+
+  nsresult rv = doc->InitializeFrameLoader(this);
+  if (NS_FAILED(rv)) {
+    mPendingSwitchID = 0;
+    mTriggeringPrincipal = nullptr;
+    mCsp = nullptr;
+
+    FireErrorEvent();
+  }
+}
+
+nsresult nsFrameLoader::ReallyStartLoading() {
+  nsresult rv = ReallyStartLoadingInternal();
+  if (NS_FAILED(rv)) {
+    FireErrorEvent();
+  }
+
+  return rv;
+}
+
+nsresult nsFrameLoader::ReallyStartLoadingInternal() {
+  NS_ENSURE_STATE((mURIToLoad || mPendingSwitchID) && mOwnerContent &&
+                  mOwnerContent->IsInComposedDoc());
+
+  AUTO_PROFILER_LABEL("nsFrameLoader::ReallyStartLoadingInternal", OTHER);
+  RefPtr<nsDocShellLoadState> loadState;
+  if (!mPendingSwitchID) {
+    loadState = new nsDocShellLoadState(mURIToLoad);
+    loadState->SetOriginalFrameSrc(mLoadingOriginalSrc);
+
+    // The triggering principal could be null if the frame is loaded other
+    // than the src attribute, for example, the frame is sandboxed. In that
+    // case we use the principal of the owner content, which is needed to
+    // prevent XSS attaches on documents loaded in subframes.
+    if (mTriggeringPrincipal) {
+      loadState->SetTriggeringPrincipal(mTriggeringPrincipal);
+    } else {
+      loadState->SetTriggeringPrincipal(mOwnerContent->NodePrincipal());
+    }
+
+    // If we have an explicit CSP, we set it. If not, we only query it from
+    // the document in case there was no explicit triggeringPrincipal.
+    // Otherwise it's possible that the original triggeringPrincipal did not
+    // have a CSP which causes the CSP on the Principal and explicit CSP
+    // to be out of sync.
+    if (mCsp) {
+      loadState->SetCsp(mCsp);
+    } else if (!mTriggeringPrincipal) {
+      nsCOMPtr<nsIContentSecurityPolicy> csp = mOwnerContent->GetCsp();
+      loadState->SetCsp(csp);
+    }
+
+    nsAutoString srcdoc;
+    bool isSrcdoc =
+        mOwnerContent->IsHTMLElement(nsGkAtoms::iframe) &&
+        mOwnerContent->GetAttr(kNameSpaceID_None, nsGkAtoms::srcdoc, srcdoc);
+
+    if (isSrcdoc) {
+      loadState->SetSrcdocData(srcdoc);
+      loadState->SetBaseURI(mOwnerContent->GetBaseURI());
+    }
+
+    auto referrerInfo = MakeRefPtr<ReferrerInfo>(*mOwnerContent);
+    loadState->SetReferrerInfo(referrerInfo);
+
+    loadState->SetIsFromProcessingFrameAttributes();
+
+    // Default flags:
+    int32_t flags = nsIWebNavigation::LOAD_FLAGS_NONE;
+
+    // Flags for browser frame:
+    if (OwnerIsMozBrowserFrame()) {
+      flags = nsIWebNavigation::LOAD_FLAGS_ALLOW_THIRD_PARTY_FIXUP |
+              nsIWebNavigation::LOAD_FLAGS_DISALLOW_INHERIT_PRINCIPAL;
+    }
+    loadState->SetLoadFlags(flags);
+
+    loadState->SetFirstParty(false);
+
+    // If we're loading the default about:blank document in a <browser> element,
+    // prevent the load from causing a process switch by explicitly overriding
+    // remote type selection.
+    if (mPendingBrowsingContext->IsTopContent() &&
+        mOwnerContent->IsXULElement(nsGkAtoms::browser) &&
+        NS_IsAboutBlank(mURIToLoad) &&
+        loadState->TriggeringPrincipal()->IsSystemPrincipal()) {
+      loadState->SetRemoteTypeOverride(mRemoteType);
+    }
+  }
+
+  if (IsRemoteFrame()) {
+    if (!EnsureRemoteBrowser()) {
+      NS_WARNING("Couldn't create child process for iframe.");
+      return NS_ERROR_FAILURE;
+    }
+
+    if (mPendingSwitchID) {
+      mRemoteBrowser->ResumeLoad(mPendingSwitchID);
+      mPendingSwitchID = 0;
+    } else {
+      mRemoteBrowser->LoadURL(loadState);
+    }
+
+    if (!mRemoteBrowserShown) {
+      // This can fail if it's too early to show the frame, we will retry later.
+      Unused << ShowRemoteFrame(ScreenIntSize(0, 0));
+    }
+
+    return NS_OK;
+  }
+
+  nsresult rv = MaybeCreateDocShell();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  MOZ_ASSERT(GetDocShell(),
+             "MaybeCreateDocShell succeeded with a null docShell");
+
+  // If we have a pending switch, just resume our load.
+  if (mPendingSwitchID) {
+    bool tmpState = mNeedsAsyncDestroy;
+    mNeedsAsyncDestroy = true;
+    rv = GetDocShell()->ResumeRedirectedLoad(mPendingSwitchID, -1);
+    mNeedsAsyncDestroy = tmpState;
+    mPendingSwitchID = 0;
+    return rv;
+  }
+
+  // Just to be safe, recheck uri.
+  rv = CheckURILoad(mURIToLoad, mTriggeringPrincipal);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  mLoadingOriginalSrc = false;
+
+  // Kick off the load...
+  bool tmpState = mNeedsAsyncDestroy;
+  mNeedsAsyncDestroy = true;
+
+  RefPtr<nsDocShell> docShell = GetDocShell();
+  rv = docShell->LoadURI(loadState, false);
+  mNeedsAsyncDestroy = tmpState;
+  mURIToLoad = nullptr;
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+nsresult nsFrameLoader::CheckURILoad(nsIURI* aURI,
+                                     nsIPrincipal* aTriggeringPrincipal) {
+  // Check for security.  The fun part is trying to figure out what principals
+  // to use.  The way I figure it, if we're doing a LoadFrame() accidentally
+  // (eg someone created a frame/iframe node, we're being parsed, XUL iframes
+  // are being reframed, etc.) then we definitely want to use the node
+  // principal of mOwnerContent for security checks.  If, on the other hand,
+  // someone's setting the src on our owner content, or created it via script,
+  // or whatever, then they can clearly access it... and we should still use
+  // the principal of mOwnerContent.  I don't think that leads to privilege
+  // escalation, and it's reasonably guaranteed to not lead to XSS issues
+  // (since caller can already access mOwnerContent in this case).  So just use
+  // the principal of mOwnerContent no matter what.  If script wants to run
+  // things with its own permissions, which differ from those of mOwnerContent
+  // (which means the script is privileged in some way) it should set
+  // window.location instead.
+  nsIScriptSecurityManager* secMan = nsContentUtils::GetSecurityManager();
+
+  // Get our principal
+  nsIPrincipal* principal =
+      (aTriggeringPrincipal ? aTriggeringPrincipal
+                            : mOwnerContent->NodePrincipal());
+
+  // Check if we are allowed to load absURL
+  nsresult rv = secMan->CheckLoadURIWithPrincipal(
+      principal, aURI, nsIScriptSecurityManager::STANDARD,
+      mOwnerContent->OwnerDoc()->InnerWindowID());
+  if (NS_FAILED(rv)) {
+    return rv;  // We're not
+  }
+
+  // Bail out if this is an infinite recursion scenario
+  if (IsRemoteFrame()) {
+    return NS_OK;
+  }
+  return CheckForRecursiveLoad(aURI);
+}
+
+nsDocShell* nsFrameLoader::GetDocShell(ErrorResult& aRv) {
+  if (IsRemoteFrame()) {
+    return nullptr;
+  }
+
+  // If we have an owner, make sure we have a docshell and return
+  // that. If not, we're most likely in the middle of being torn down,
+  // then we just return null.
+  if (mOwnerContent) {
+    nsresult rv = MaybeCreateDocShell();
+    if (NS_FAILED(rv)) {
+      aRv.Throw(rv);
+      return nullptr;
+    }
+    MOZ_ASSERT(GetDocShell(),
+               "MaybeCreateDocShell succeeded, but null docShell");
+  }
+
+  return GetDocShell();
+}
+
+static void SetTreeOwnerAndChromeEventHandlerOnDocshellTree(
+    nsIDocShellTreeItem* aItem, nsIDocShellTreeOwner* aOwner,
+    EventTarget* aHandler) {
+  MOZ_ASSERT(aItem, "Must have item");
+
+  aItem->SetTreeOwner(aOwner);
+
+  int32_t childCount = 0;
+  aItem->GetInProcessChildCount(&childCount);
+  for (int32_t i = 0; i < childCount; ++i) {
+    nsCOMPtr<nsIDocShellTreeItem> item;
+    aItem->GetInProcessChildAt(i, getter_AddRefs(item));
+    if (aHandler) {
+      nsCOMPtr<nsIDocShell> shell(do_QueryInterface(item));
+      shell->SetChromeEventHandler(aHandler);
+    }
+    SetTreeOwnerAndChromeEventHandlerOnDocshellTree(item, aOwner, aHandler);
+  }
+}
+
+#if defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
+static bool CheckDocShellType(mozilla::dom::Element* aOwnerContent,
+                              nsIDocShellTreeItem* aDocShell, nsAtom* aAtom) {
+  bool isContent = aOwnerContent->AttrValueIs(kNameSpaceID_None, aAtom,
+                                              nsGkAtoms::content, eIgnoreCase);
+
+  if (!isContent) {
+    nsCOMPtr<nsIMozBrowserFrame> mozbrowser =
+        aOwnerContent->GetAsMozBrowserFrame();
+    if (mozbrowser) {
+      mozbrowser->GetMozbrowser(&isContent);
+    }
+  }
+
+  if (isContent) {
+    return aDocShell->ItemType() == nsIDocShellTreeItem::typeContent;
+  }
+
+  nsCOMPtr<nsIDocShellTreeItem> parent;
+  aDocShell->GetInProcessParent(getter_AddRefs(parent));
+
+  return parent && parent->ItemType() == aDocShell->ItemType();
+}
+#endif  // defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
+
+/**
+ * Hook up a given TreeItem to its tree owner. aItem's type must have already
+ * been set, and it should already be part of the DocShellTree.
+ * @param aItem the treeitem we're working with
+ * @param aTreeOwner the relevant treeowner; might be null
+ */
+void nsFrameLoader::AddTreeItemToTreeOwner(nsIDocShellTreeItem* aItem,
+                                           nsIDocShellTreeOwner* aOwner) {
+  MOZ_ASSERT(aItem, "Must have docshell treeitem");
+  MOZ_ASSERT(mOwnerContent, "Must have owning content");
+
+  MOZ_DIAGNOSTIC_ASSERT(
+      CheckDocShellType(mOwnerContent, aItem, TypeAttrName(mOwnerContent)),
+      "Correct ItemType should be set when creating BrowsingContext");
+
+  if (mIsTopLevelContent) {
+    bool is_primary = mOwnerContent->AttrValueIs(
+        kNameSpaceID_None, nsGkAtoms::primary, nsGkAtoms::_true, eIgnoreCase);
+    if (aOwner) {
+      mOwnerContent->AddMutationObserver(this);
+      mObservingOwnerContent = true;
+      aOwner->ContentShellAdded(aItem, is_primary);
+    }
+  }
+}
+
+static bool AllDescendantsOfType(BrowsingContext* aParent,
+                                 BrowsingContext::Type aType) {
+  for (auto& child : aParent->Children()) {
+    if (child->GetType() != aType || !AllDescendantsOfType(child, aType)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+void nsFrameLoader::MaybeShowFrame() {
+  nsIFrame* frame = GetPrimaryFrameOfOwningContent();
+  if (frame) {
+    nsSubDocumentFrame* subDocFrame = do_QueryFrame(frame);
+    if (subDocFrame) {
+      subDocFrame->MaybeShowViewer();
+    }
+  }
+}
+
+static ScrollbarPreference GetScrollbarPreference(const Element* aOwner) {
+  if (!aOwner) {
+    return ScrollbarPreference::Auto;
+  }
+  const nsAttrValue* attrValue = aOwner->GetParsedAttr(nsGkAtoms::scrolling);
+  return nsGenericHTMLFrameElement::MapScrollingAttribute(attrValue);
+}
+
+static CSSIntSize GetMarginAttributes(const Element* aOwner) {
+  CSSIntSize result(-1, -1);
+  auto* content = nsGenericHTMLElement::FromNodeOrNull(aOwner);
+  if (!content) {
+    return result;
+  }
+  const nsAttrValue* attr = content->GetParsedAttr(nsGkAtoms::marginwidth);
+  if (attr && attr->Type() == nsAttrValue::eInteger) {
+    result.width = attr->GetIntegerValue();
+  }
+  attr = content->GetParsedAttr(nsGkAtoms::marginheight);
+  if (attr && attr->Type() == nsAttrValue::eInteger) {
+    result.height = attr->GetIntegerValue();
+  }
+  return result;
+}
+
+bool nsFrameLoader::Show(nsSubDocumentFrame* frame) {
+  if (mInShow) {
+    return false;
+  }
+  mInShow = true;
+
+  auto resetInShow = mozilla::MakeScopeExit([&] { mInShow = false; });
+
+  ScreenIntSize size = frame->GetSubdocumentSize();
+  if (IsRemoteFrame()) {
+    // FIXME(bug 1588791): For fission iframes we need to pass down the
+    // scrollbar preferences.
+    return ShowRemoteFrame(size, frame);
+  }
+
+  nsresult rv = MaybeCreateDocShell();
+  if (NS_FAILED(rv)) {
+    return false;
+  }
+  nsDocShell* ds = GetDocShell();
+  MOZ_ASSERT(ds, "MaybeCreateDocShell succeeded, but null docShell");
+  if (!ds) {
+    return false;
+  }
+
+  ds->SetScrollbarPreference(GetScrollbarPreference(mOwnerContent));
+  const bool marginsChanged =
+      ds->UpdateFrameMargins(GetMarginAttributes(mOwnerContent));
+  if (PresShell* presShell = ds->GetPresShell()) {
+    // Ensure root scroll frame is reflowed in case margins have changed
+    if (marginsChanged) {
+      if (nsIFrame* rootScrollFrame = presShell->GetRootScrollFrame()) {
+        presShell->FrameNeedsReflow(rootScrollFrame, IntrinsicDirty::None,
+                                    NS_FRAME_IS_DIRTY);
+      }
+    }
+    return true;
+  }
+
+  nsView* view = frame->EnsureInnerView();
+  if (!view) return false;
+
+  RefPtr<nsDocShell> baseWindow = GetDocShell();
+  baseWindow->InitWindow(nullptr, view->GetWidget(), 0, 0, size.width,
+                         size.height);
+  baseWindow->SetVisibility(true);
+  NS_ENSURE_TRUE(GetDocShell(), false);
+
+  // Trigger editor re-initialization if midas is turned on in the
+  // sub-document. This shouldn't be necessary, but given the way our
+  // editor works, it is. See
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=284245
+  if (RefPtr<PresShell> presShell = GetDocShell()->GetPresShell()) {
+    Document* doc = presShell->GetDocument();
+    nsHTMLDocument* htmlDoc =
+        doc && doc->IsHTMLOrXHTML() ? doc->AsHTMLDocument() : nullptr;
+
+    if (htmlDoc) {
+      nsAutoString designMode;
+      htmlDoc->GetDesignMode(designMode);
+
+      if (designMode.EqualsLiteral("on")) {
+        // Hold on to the editor object to let the document reattach to the
+        // same editor object, instead of creating a new one.
+        RefPtr<HTMLEditor> htmlEditor = GetDocShell()->GetHTMLEditor();
+        Unused << htmlEditor;
+        htmlDoc->SetDesignMode(u"off"_ns, Nothing(), IgnoreErrors());
+
+        htmlDoc->SetDesignMode(u"on"_ns, Nothing(), IgnoreErrors());
+      } else {
+        // Re-initialize the presentation for contenteditable documents
+        bool editable = false, hasEditingSession = false;
+        GetDocShell()->GetEditable(&editable);
+        GetDocShell()->GetHasEditingSession(&hasEditingSession);
+        RefPtr<HTMLEditor> htmlEditor = GetDocShell()->GetHTMLEditor();
+        if (editable && hasEditingSession && htmlEditor) {
+          htmlEditor->PostCreate();
+        }
+      }
+    }
+  }
+
+  mInShow = false;
+  if (mHideCalled) {
+    mHideCalled = false;
+    Hide();
+    return false;
+  }
+  return true;
+}
+
+void nsFrameLoader::MarginsChanged() {
+  // We assume that the margins are always zero for remote frames.
+  if (IsRemoteFrame()) {
+    return;
+  }
+
+  nsDocShell* docShell = GetDocShell();
+  // If there's no docshell, we're probably not up and running yet.
+  // nsFrameLoader::Show() will take care of setting the right
+  // margins.
+  if (!docShell) {
+    return;
+  }
+
+  if (!docShell->UpdateFrameMargins(GetMarginAttributes(mOwnerContent))) {
+    return;
+  }
+
+  // There's a cached property declaration block
+  // that needs to be updated
+  if (Document* doc = docShell->GetDocument()) {
+    for (nsINode* cur = doc; cur; cur = cur->GetNextNode()) {
+      if (cur->IsHTMLElement(nsGkAtoms::body)) {
+        static_cast<HTMLBodyElement*>(cur)->ClearMappedServoStyle();
+      }
+    }
+  }
+
+  // Trigger a restyle if there's a prescontext
+  // FIXME: This could do something much less expensive.
+  if (nsPresContext* presContext = docShell->GetPresContext()) {
+    // rebuild, because now the same nsMappedAttributes* will produce
+    // a different style
+    presContext->RebuildAllStyleData(nsChangeHint(0),
+                                     RestyleHint::RestyleSubtree());
+  }
+}
+
+bool nsFrameLoader::ShowRemoteFrame(const ScreenIntSize& size,
+                                    nsSubDocumentFrame* aFrame) {
+  AUTO_PROFILER_LABEL("nsFrameLoader::ShowRemoteFrame", OTHER);
+  NS_ASSERTION(IsRemoteFrame(),
+               "ShowRemote only makes sense on remote frames.");
+
+  if (!EnsureRemoteBrowser()) {
+    NS_ERROR("Couldn't create child process.");
+    return false;
+  }
+
+  // FIXME/bug 589337: Show()/Hide() is pretty expensive for
+  // cross-process layers; need to figure out what behavior we really
+  // want here.  For now, hack.
+  if (!mRemoteBrowserShown) {
+    if (!mOwnerContent || !mOwnerContent->GetComposedDoc()) {
+      return false;
+    }
+
+    // We never want to host remote frameloaders in simple popups, like menus.
+    nsIWidget* widget = nsContentUtils::WidgetForContent(mOwnerContent);
+    if (!widget || static_cast<nsBaseWidget*>(widget)->IsSmallPopup()) {
+      return false;
+    }
+
+    if (BrowserHost* bh = mRemoteBrowser->AsBrowserHost()) {
+      RefPtr<BrowsingContext> bc = bh->GetBrowsingContext()->Top();
+
+      // Set to the current activation of the window.
+      bc->SetIsActiveBrowserWindow(bc->GetIsActiveBrowserWindow());
+    }
+
+    nsCOMPtr<nsISupports> container = mOwnerContent->OwnerDoc()->GetContainer();
+    nsCOMPtr<nsIBaseWindow> baseWindow = do_QueryInterface(container);
+    nsCOMPtr<nsIWidget> mainWidget;
+    baseWindow->GetMainWidget(getter_AddRefs(mainWidget));
+    nsSizeMode sizeMode =
+        mainWidget ? mainWidget->SizeMode() : nsSizeMode_Normal;
+    OwnerShowInfo info(size, GetScrollbarPreference(mOwnerContent), sizeMode);
+    if (!mRemoteBrowser->Show(info)) {
+      return false;
+    }
+    mRemoteBrowserShown = true;
+
+    // This notification doesn't apply to fission, apparently.
+    if (!GetBrowserBridgeChild()) {
+      if (nsCOMPtr<nsIObserverService> os = services::GetObserverService()) {
+        os->NotifyObservers(ToSupports(this), "remote-browser-shown", nullptr);
+      }
+      ProcessPriorityManager::RemoteBrowserFrameShown(this);
+    }
+  } else {
+    nsIntRect dimensions;
+    NS_ENSURE_SUCCESS(GetWindowDimensions(dimensions), false);
+
+    // Don't show remote iframe if we are waiting for the completion of reflow.
+    if (!aFrame || !aFrame->HasAnyStateBits(NS_FRAME_FIRST_REFLOW)) {
+      mRemoteBrowser->UpdateDimensions(dimensions, size);
+    }
+  }
+
+  return true;
+}
+
+void nsFrameLoader::Hide() {
+  if (mHideCalled) {
+    return;
+  }
+  if (mInShow) {
+    mHideCalled = true;
+    return;
+  }
+
+  if (!GetDocShell()) {
+    return;
+  }
+
+  nsCOMPtr<nsIContentViewer> contentViewer;
+  GetDocShell()->GetContentViewer(getter_AddRefs(contentViewer));
+  if (contentViewer) contentViewer->SetSticky(false);
+
+  RefPtr<nsDocShell> baseWin = GetDocShell();
+  baseWin->SetVisibility(false);
+  baseWin->SetParentWidget(nullptr);
+}
+
+void nsFrameLoader::ForceLayoutIfNecessary() {
+  nsIFrame* frame = GetPrimaryFrameOfOwningContent();
+  if (!frame) {
+    return;
+  }
+
+  nsPresContext* presContext = frame->PresContext();
+  if (!presContext) {
+    return;
+  }
+
+  // Only force the layout flush if the frameloader hasn't ever been
+  // run through layout.
+  if (frame->HasAnyStateBits(NS_FRAME_FIRST_REFLOW)) {
+    if (RefPtr<PresShell> presShell = presContext->GetPresShell()) {
+      presShell->FlushPendingNotifications(FlushType::Layout);
+    }
+  }
+}
+
+nsresult nsFrameLoader::SwapWithOtherRemoteLoader(
+    nsFrameLoader* aOther, nsFrameLoaderOwner* aThisOwner,
+    nsFrameLoaderOwner* aOtherOwner) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+#ifdef DEBUG
+  RefPtr<nsFrameLoader> first = aThisOwner->GetFrameLoader();
+  RefPtr<nsFrameLoader> second = aOtherOwner->GetFrameLoader();
+  MOZ_ASSERT(first == this, "aThisOwner must own this");
+  MOZ_ASSERT(second == aOther, "aOtherOwner must own aOther");
+#endif
+
+  Element* ourContent = mOwnerContent;
+  Element* otherContent = aOther->mOwnerContent;
+
+  if (!ourContent || !otherContent) {
+    // Can't handle this
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  // Make sure there are no same-origin issues
+  bool equal;
+  nsresult rv = ourContent->NodePrincipal()->Equals(
+      otherContent->NodePrincipal(), &equal);
+  if (NS_FAILED(rv) || !equal) {
+    // Security problems loom.  Just bail on it all
+    return NS_ERROR_DOM_SECURITY_ERR;
+  }
+
+  Document* ourDoc = ourContent->GetComposedDoc();
+  Document* otherDoc = otherContent->GetComposedDoc();
+  if (!ourDoc || !otherDoc) {
+    // Again, how odd, given that we had docshells
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  PresShell* ourPresShell = ourDoc->GetPresShell();
+  PresShell* otherPresShell = otherDoc->GetPresShell();
+  if (!ourPresShell || !otherPresShell) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  auto* browserParent = GetBrowserParent();
+  auto* otherBrowserParent = aOther->GetBrowserParent();
+
+  if (!browserParent || !otherBrowserParent) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  RefPtr<BrowsingContext> ourBc = browserParent->GetBrowsingContext();
+  RefPtr<BrowsingContext> otherBc = otherBrowserParent->GetBrowsingContext();
+
+  // When we swap docShells, maybe we have to deal with a new page created just
+  // for this operation. In this case, the browser code should already have set
+  // the correct userContextId attribute value in the owning element, but our
+  // docShell, that has been created way before) doesn't know that that
+  // happened.
+  // This is the reason why now we must retrieve the correct value from the
+  // usercontextid attribute before comparing our originAttributes with the
+  // other one.
+  OriginAttributes ourOriginAttributes = ourBc->OriginAttributesRef();
+  rv = PopulateOriginContextIdsFromAttributes(ourOriginAttributes);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  OriginAttributes otherOriginAttributes = otherBc->OriginAttributesRef();
+  rv = aOther->PopulateOriginContextIdsFromAttributes(otherOriginAttributes);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (!ourOriginAttributes.EqualsIgnoringFPD(otherOriginAttributes)) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  bool ourHasHistory =
+      mIsTopLevelContent && ourContent->IsXULElement(nsGkAtoms::browser) &&
+      !ourContent->HasAttr(kNameSpaceID_None, nsGkAtoms::disablehistory);
+  bool otherHasHistory =
+      aOther->mIsTopLevelContent &&
+      otherContent->IsXULElement(nsGkAtoms::browser) &&
+      !otherContent->HasAttr(kNameSpaceID_None, nsGkAtoms::disablehistory);
+  if (ourHasHistory != otherHasHistory) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  if (mInSwap || aOther->mInSwap) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  mInSwap = aOther->mInSwap = true;
+
+  // NOTE(emilio): This doesn't have to flush because the caller does already.
+  nsIFrame* ourFrame = ourContent->GetPrimaryFrame();
+  nsIFrame* otherFrame = otherContent->GetPrimaryFrame();
+  if (!ourFrame || !otherFrame) {
+    mInSwap = aOther->mInSwap = false;
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  nsSubDocumentFrame* ourFrameFrame = do_QueryFrame(ourFrame);
+  if (!ourFrameFrame) {
+    mInSwap = aOther->mInSwap = false;
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  rv = ourFrameFrame->BeginSwapDocShells(otherFrame);
+  if (NS_FAILED(rv)) {
+    mInSwap = aOther->mInSwap = false;
+    return rv;
+  }
+
+  nsCOMPtr<nsIBrowserDOMWindow> otherBrowserDOMWindow =
+      otherBrowserParent->GetBrowserDOMWindow();
+  nsCOMPtr<nsIBrowserDOMWindow> browserDOMWindow =
+      browserParent->GetBrowserDOMWindow();
+
+  if (!!otherBrowserDOMWindow != !!browserDOMWindow) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  // Destroy browser frame scripts for content leaving a frame with browser API
+  if (OwnerIsMozBrowserFrame() && !aOther->OwnerIsMozBrowserFrame()) {
+    DestroyBrowserFrameScripts();
+  }
+  if (!OwnerIsMozBrowserFrame() && aOther->OwnerIsMozBrowserFrame()) {
+    aOther->DestroyBrowserFrameScripts();
+  }
+
+  otherBrowserParent->SetBrowserDOMWindow(browserDOMWindow);
+  browserParent->SetBrowserDOMWindow(otherBrowserDOMWindow);
+
+  MaybeUpdatePrimaryBrowserParent(eBrowserParentRemoved);
+  aOther->MaybeUpdatePrimaryBrowserParent(eBrowserParentRemoved);
+
+  if (mozilla::BFCacheInParent() && XRE_IsParentProcess()) {
+    // nsFrameLoaders in session history can't be moved to another owner since
+    // there are no corresponging message managers on which swap can be done.
+    // See the line mMessageManager.swap(aOther->mMessageManager); below.
+    auto evict = [](nsFrameLoader* aFrameLoader) {
+      if (BrowsingContext* bc =
+              aFrameLoader->GetMaybePendingBrowsingContext()) {
+        nsCOMPtr<nsISHistory> shistory = bc->Canonical()->GetSessionHistory();
+        if (shistory) {
+          shistory->EvictAllContentViewers();
+        }
+      }
+    };
+    evict(this);
+    evict(aOther);
+  }
+
+  SetOwnerContent(otherContent);
+  aOther->SetOwnerContent(ourContent);
+
+  browserParent->SetOwnerElement(otherContent);
+  otherBrowserParent->SetOwnerElement(ourContent);
+
+  // Update window activation state for the swapped owner content.
+  bool ourActive = otherBc->GetIsActiveBrowserWindow();
+  bool otherActive = ourBc->GetIsActiveBrowserWindow();
+  if (ourBc->IsTop()) {
+    ourBc->SetIsActiveBrowserWindow(otherActive);
+  }
+  if (otherBc->IsTop()) {
+    otherBc->SetIsActiveBrowserWindow(ourActive);
+  }
+
+  MaybeUpdatePrimaryBrowserParent(eBrowserParentChanged);
+  aOther->MaybeUpdatePrimaryBrowserParent(eBrowserParentChanged);
+
+  RefPtr<nsFrameMessageManager> ourMessageManager = mMessageManager;
+  RefPtr<nsFrameMessageManager> otherMessageManager = aOther->mMessageManager;
+  // Swap and setup things in parent message managers.
+  if (ourMessageManager) {
+    ourMessageManager->SetCallback(aOther);
+  }
+  if (otherMessageManager) {
+    otherMessageManager->SetCallback(this);
+  }
+  mMessageManager.swap(aOther->mMessageManager);
+
+  // XXXsmaug what should be done to JSWindowActorParent objects when swapping
+  // frameloaders? Currently they leak very easily, bug 1697918.
+
+  // Perform the actual swap of the internal refptrs. We keep a strong reference
+  // to ourselves to make sure we don't die while we overwrite our reference to
+  // ourself.
+  RefPtr<nsFrameLoader> kungFuDeathGrip(this);
+  aThisOwner->SetFrameLoader(aOther);
+  aOtherOwner->SetFrameLoader(kungFuDeathGrip);
+
+  ourFrameFrame->EndSwapDocShells(otherFrame);
+
+  ourPresShell->BackingScaleFactorChanged();
+  otherPresShell->BackingScaleFactorChanged();
+
+  // Initialize browser API if needed now that owner content has changed.
+  InitializeBrowserAPI();
+  aOther->InitializeBrowserAPI();
+
+  mInSwap = aOther->mInSwap = false;
+
+  // Send an updated tab context since owner content type may have changed.
+  MutableTabContext ourContext;
+  rv = GetNewTabContext(&ourContext);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  MutableTabContext otherContext;
+  rv = aOther->GetNewTabContext(&otherContext);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  Unused << browserParent->SendSwappedWithOtherRemoteLoader(
+      ourContext.AsIPCTabContext());
+  Unused << otherBrowserParent->SendSwappedWithOtherRemoteLoader(
+      otherContext.AsIPCTabContext());
+  return NS_OK;
+}
+
+class MOZ_RAII AutoResetInFrameSwap final {
+ public:
+  AutoResetInFrameSwap(nsFrameLoader* aThisFrameLoader,
+                       nsFrameLoader* aOtherFrameLoader,
+                       nsDocShell* aThisDocShell, nsDocShell* aOtherDocShell,
+                       EventTarget* aThisEventTarget,
+                       EventTarget* aOtherEventTarget)
+      : mThisFrameLoader(aThisFrameLoader),
+        mOtherFrameLoader(aOtherFrameLoader),
+        mThisDocShell(aThisDocShell),
+        mOtherDocShell(aOtherDocShell),
+        mThisEventTarget(aThisEventTarget),
+        mOtherEventTarget(aOtherEventTarget) {
+    mThisFrameLoader->mInSwap = true;
+    mOtherFrameLoader->mInSwap = true;
+    mThisDocShell->SetInFrameSwap(true);
+    mOtherDocShell->SetInFrameSwap(true);
+
+    // Fire pageshow events on still-loading pages, and then fire pagehide
+    // events.  Note that we do NOT fire these in the normal way, but just fire
+    // them on the chrome event handlers.
+    nsContentUtils::FirePageShowEventForFrameLoaderSwap(
+        mThisDocShell, mThisEventTarget, false);
+    nsContentUtils::FirePageShowEventForFrameLoaderSwap(
+        mOtherDocShell, mOtherEventTarget, false);
+    nsContentUtils::FirePageHideEventForFrameLoaderSwap(mThisDocShell,
+                                                        mThisEventTarget);
+    nsContentUtils::FirePageHideEventForFrameLoaderSwap(mOtherDocShell,
+                                                        mOtherEventTarget);
+  }
+
+  ~AutoResetInFrameSwap() {
+    nsContentUtils::FirePageShowEventForFrameLoaderSwap(mThisDocShell,
+                                                        mThisEventTarget, true);
+    nsContentUtils::FirePageShowEventForFrameLoaderSwap(
+        mOtherDocShell, mOtherEventTarget, true);
+
+    mThisFrameLoader->mInSwap = false;
+    mOtherFrameLoader->mInSwap = false;
+    mThisDocShell->SetInFrameSwap(false);
+    mOtherDocShell->SetInFrameSwap(false);
+
+    // This is needed to get visibility state right in cases when we swapped a
+    // visible tab (foreground in visible window) with a non-visible tab.
+    if (RefPtr<Document> doc = mThisDocShell->GetDocument()) {
+      doc->UpdateVisibilityState();
+    }
+    if (RefPtr<Document> doc = mOtherDocShell->GetDocument()) {
+      doc->UpdateVisibilityState();
+    }
+  }
+
+ private:
+  RefPtr<nsFrameLoader> mThisFrameLoader;
+  RefPtr<nsFrameLoader> mOtherFrameLoader;
+  RefPtr<nsDocShell> mThisDocShell;
+  RefPtr<nsDocShell> mOtherDocShell;
+  nsCOMPtr<EventTarget> mThisEventTarget;
+  nsCOMPtr<EventTarget> mOtherEventTarget;
+};
+
+nsresult nsFrameLoader::SwapWithOtherLoader(nsFrameLoader* aOther,
+                                            nsFrameLoaderOwner* aThisOwner,
+                                            nsFrameLoaderOwner* aOtherOwner) {
+#ifdef DEBUG
+  RefPtr<nsFrameLoader> first = aThisOwner->GetFrameLoader();
+  RefPtr<nsFrameLoader> second = aOtherOwner->GetFrameLoader();
+  MOZ_ASSERT(first == this, "aThisOwner must own this");
+  MOZ_ASSERT(second == aOther, "aOtherOwner must own aOther");
+#endif
+
+  NS_ENSURE_STATE(!mInShow && !aOther->mInShow);
+
+  if (IsRemoteFrame() != aOther->IsRemoteFrame()) {
+    NS_WARNING(
+        "Swapping remote and non-remote frames is not currently supported");
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  RefPtr<Element> ourContent = mOwnerContent;
+  RefPtr<Element> otherContent = aOther->mOwnerContent;
+  if (!ourContent || !otherContent) {
+    // Can't handle this
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  nsIFrame* ourFrame = ourContent->GetPrimaryFrame(FlushType::Frames);
+  nsIFrame* otherFrame = otherContent->GetPrimaryFrame(FlushType::Frames);
+  if (!ourFrame || !otherFrame) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  // Ensure the flushes above haven't changed all the world.
+  if (ourContent != mOwnerContent || otherContent != aOther->mOwnerContent) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  bool ourHasSrcdoc = ourContent->IsHTMLElement(nsGkAtoms::iframe) &&
+                      ourContent->HasAttr(kNameSpaceID_None, nsGkAtoms::srcdoc);
+  bool otherHasSrcdoc =
+      otherContent->IsHTMLElement(nsGkAtoms::iframe) &&
+      otherContent->HasAttr(kNameSpaceID_None, nsGkAtoms::srcdoc);
+  if (ourHasSrcdoc || otherHasSrcdoc) {
+    // Ignore this case entirely for now, since we support XUL <-> HTML swapping
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  bool ourFullscreenAllowed = ourContent->IsXULElement() ||
+                              (OwnerIsMozBrowserFrame() &&
+                               ourContent->HasAttr(nsGkAtoms::allowfullscreen));
+  bool otherFullscreenAllowed =
+      otherContent->IsXULElement() ||
+      (aOther->OwnerIsMozBrowserFrame() &&
+       otherContent->HasAttr(nsGkAtoms::allowfullscreen));
+  if (ourFullscreenAllowed != otherFullscreenAllowed) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  nsILoadContext* ourLoadContext = ourContent->OwnerDoc()->GetLoadContext();
+  nsILoadContext* otherLoadContext = otherContent->OwnerDoc()->GetLoadContext();
+  MOZ_ASSERT(ourLoadContext && otherLoadContext,
+             "Swapping frames within dead documents?");
+  if (ourLoadContext->UseRemoteTabs() != otherLoadContext->UseRemoteTabs()) {
+    NS_WARNING("Can't swap between e10s and non-e10s windows");
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  if (ourLoadContext->UseRemoteSubframes() !=
+      otherLoadContext->UseRemoteSubframes()) {
+    NS_WARNING("Can't swap between fission and non-fission windows");
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  // Divert to a separate path for the remaining steps in the remote case
+  if (IsRemoteFrame()) {
+    MOZ_ASSERT(aOther->IsRemoteFrame());
+    return SwapWithOtherRemoteLoader(aOther, aThisOwner, aOtherOwner);
+  }
+
+  // Make sure there are no same-origin issues
+  bool equal;
+  nsresult rv = ourContent->NodePrincipal()->Equals(
+      otherContent->NodePrincipal(), &equal);
+  if (NS_FAILED(rv) || !equal) {
+    // Security problems loom.  Just bail on it all
+    return NS_ERROR_DOM_SECURITY_ERR;
+  }
+
+  RefPtr<nsDocShell> ourDocshell = GetExistingDocShell();
+  RefPtr<nsDocShell> otherDocshell = aOther->GetExistingDocShell();
+  if (!ourDocshell || !otherDocshell) {
+    // How odd
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  // To avoid having to mess with session history, avoid swapping
+  // frameloaders that don't correspond to root same-type docshells,
+  // unless both roots have session history disabled.
+  nsCOMPtr<nsIDocShellTreeItem> ourRootTreeItem, otherRootTreeItem;
+  ourDocshell->GetInProcessSameTypeRootTreeItem(
+      getter_AddRefs(ourRootTreeItem));
+  otherDocshell->GetInProcessSameTypeRootTreeItem(
+      getter_AddRefs(otherRootTreeItem));
+  nsCOMPtr<nsIWebNavigation> ourRootWebnav = do_QueryInterface(ourRootTreeItem);
+  nsCOMPtr<nsIWebNavigation> otherRootWebnav =
+      do_QueryInterface(otherRootTreeItem);
+
+  if (!ourRootWebnav || !otherRootWebnav) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  RefPtr<ChildSHistory> ourHistory = ourRootWebnav->GetSessionHistory();
+  RefPtr<ChildSHistory> otherHistory = otherRootWebnav->GetSessionHistory();
+
+  if ((ourRootTreeItem != ourDocshell || otherRootTreeItem != otherDocshell) &&
+      (ourHistory || otherHistory)) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  RefPtr<BrowsingContext> ourBc = ourDocshell->GetBrowsingContext();
+  RefPtr<BrowsingContext> otherBc = otherDocshell->GetBrowsingContext();
+
+  // Also make sure that the two BrowsingContexts are the same type. Otherwise
+  // swapping is certainly not safe. If this needs to be changed then
+  // the code below needs to be audited as it assumes identical types.
+  if (ourBc->GetType() != otherBc->GetType()) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  // We ensure that BCs are either both top frames or both subframes.
+  if (ourBc->IsTop() != otherBc->IsTop()) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  // One more twist here.  Setting up the right treeowners in a heterogeneous
+  // tree is a bit of a pain.  So make sure that if `ourBc->GetType()` is not
+  // nsIDocShellTreeItem::typeContent then all of our descendants are the same
+  // type as us.
+  if (!ourBc->IsContent() &&
+      (!AllDescendantsOfType(ourBc, ourBc->GetType()) ||
+       !AllDescendantsOfType(otherBc, otherBc->GetType()))) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  // Save off the tree owners, frame elements, chrome event handlers, and
+  // docshell and document parents before doing anything else.
+  nsCOMPtr<nsIDocShellTreeOwner> ourOwner, otherOwner;
+  ourDocshell->GetTreeOwner(getter_AddRefs(ourOwner));
+  otherDocshell->GetTreeOwner(getter_AddRefs(otherOwner));
+  // Note: it's OK to have null treeowners.
+
+  nsCOMPtr<nsIDocShellTreeItem> ourParentItem, otherParentItem;
+  ourDocshell->GetInProcessParent(getter_AddRefs(ourParentItem));
+  otherDocshell->GetInProcessParent(getter_AddRefs(otherParentItem));
+  if (!ourParentItem || !otherParentItem) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  nsCOMPtr<nsPIDOMWindowOuter> ourWindow = ourDocshell->GetWindow();
+  nsCOMPtr<nsPIDOMWindowOuter> otherWindow = otherDocshell->GetWindow();
+
+  nsCOMPtr<Element> ourFrameElement = ourWindow->GetFrameElementInternal();
+  nsCOMPtr<Element> otherFrameElement = otherWindow->GetFrameElementInternal();
+
+  nsCOMPtr<EventTarget> ourChromeEventHandler =
+      ourWindow->GetChromeEventHandler();
+  nsCOMPtr<EventTarget> otherChromeEventHandler =
+      otherWindow->GetChromeEventHandler();
+
+  nsCOMPtr<EventTarget> ourEventTarget = ourWindow->GetParentTarget();
+  nsCOMPtr<EventTarget> otherEventTarget = otherWindow->GetParentTarget();
+
+  NS_ASSERTION(SameCOMIdentity(ourFrameElement, ourContent) &&
+                   SameCOMIdentity(otherFrameElement, otherContent) &&
+                   SameCOMIdentity(ourChromeEventHandler, ourContent) &&
+                   SameCOMIdentity(otherChromeEventHandler, otherContent),
+               "How did that happen, exactly?");
+
+  nsCOMPtr<Document> ourChildDocument = ourWindow->GetExtantDoc();
+  nsCOMPtr<Document> otherChildDocument = otherWindow->GetExtantDoc();
+  if (!ourChildDocument || !otherChildDocument) {
+    // This shouldn't be happening
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  nsCOMPtr<Document> ourParentDocument =
+      ourChildDocument->GetInProcessParentDocument();
+  nsCOMPtr<Document> otherParentDocument =
+      otherChildDocument->GetInProcessParentDocument();
+
+  // Make sure to swap docshells between the two frames.
+  Document* ourDoc = ourContent->GetComposedDoc();
+  Document* otherDoc = otherContent->GetComposedDoc();
+  if (!ourDoc || !otherDoc) {
+    // Again, how odd, given that we had docshells
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  NS_ASSERTION(ourDoc == ourParentDocument, "Unexpected parent document");
+  NS_ASSERTION(otherDoc == otherParentDocument, "Unexpected parent document");
+
+  PresShell* ourPresShell = ourDoc->GetPresShell();
+  PresShell* otherPresShell = otherDoc->GetPresShell();
+  if (!ourPresShell || !otherPresShell) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  // When we swap docShells, maybe we have to deal with a new page created just
+  // for this operation. In this case, the browser code should already have set
+  // the correct userContextId attribute value in the owning element, but our
+  // docShell, that has been created way before) doesn't know that that
+  // happened.
+  // This is the reason why now we must retrieve the correct value from the
+  // usercontextid attribute before comparing our originAttributes with the
+  // other one.
+  OriginAttributes ourOriginAttributes = ourDocshell->GetOriginAttributes();
+  rv = PopulateOriginContextIdsFromAttributes(ourOriginAttributes);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  OriginAttributes otherOriginAttributes = otherDocshell->GetOriginAttributes();
+  rv = aOther->PopulateOriginContextIdsFromAttributes(otherOriginAttributes);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (ourOriginAttributes != otherOriginAttributes) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  if (mInSwap || aOther->mInSwap) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  AutoResetInFrameSwap autoFrameSwap(this, aOther, ourDocshell, otherDocshell,
+                                     ourEventTarget, otherEventTarget);
+
+  nsSubDocumentFrame* ourFrameFrame = do_QueryFrame(ourFrame);
+  if (!ourFrameFrame) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  // OK.  First begin to swap the docshells in the two nsIFrames
+  rv = ourFrameFrame->BeginSwapDocShells(otherFrame);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  // Destroy browser frame scripts for content leaving a frame with browser API
+  if (OwnerIsMozBrowserFrame() && !aOther->OwnerIsMozBrowserFrame()) {
+    DestroyBrowserFrameScripts();
+  }
+  if (!OwnerIsMozBrowserFrame() && aOther->OwnerIsMozBrowserFrame()) {
+    aOther->DestroyBrowserFrameScripts();
+  }
+
+  // Now move the docshells to the right docshell trees.  Note that this
+  // resets their treeowners to null.
+  ourParentItem->RemoveChild(ourDocshell);
+  otherParentItem->RemoveChild(otherDocshell);
+  if (ourBc->IsContent()) {
+    ourOwner->ContentShellRemoved(ourDocshell);
+    otherOwner->ContentShellRemoved(otherDocshell);
+  }
+
+  ourParentItem->AddChild(otherDocshell);
+  otherParentItem->AddChild(ourDocshell);
+
+  // Restore the correct chrome event handlers.
+  ourDocshell->SetChromeEventHandler(otherChromeEventHandler);
+  otherDocshell->SetChromeEventHandler(ourChromeEventHandler);
+  // Restore the correct treeowners
+  // (and also chrome event handlers for content frames only).
+  SetTreeOwnerAndChromeEventHandlerOnDocshellTree(
+      ourDocshell, otherOwner,
+      ourBc->IsContent() ? otherChromeEventHandler.get() : nullptr);
+  SetTreeOwnerAndChromeEventHandlerOnDocshellTree(
+      otherDocshell, ourOwner,
+      ourBc->IsContent() ? ourChromeEventHandler.get() : nullptr);
+
+  // Switch the owner content before we start calling AddTreeItemToTreeOwner.
+  // Note that we rely on this to deal with setting mObservingOwnerContent to
+  // false and calling RemoveMutationObserver as needed.
+  SetOwnerContent(otherContent);
+  aOther->SetOwnerContent(ourContent);
+
+  AddTreeItemToTreeOwner(ourDocshell, otherOwner);
+  aOther->AddTreeItemToTreeOwner(otherDocshell, ourOwner);
+
+  // SetSubDocumentFor nulls out parent documents on the old child doc if a
+  // new non-null document is passed in, so just go ahead and remove both
+  // kids before reinserting in the parent subdoc maps, to avoid
+  // complications.
+  ourParentDocument->SetSubDocumentFor(ourContent, nullptr);
+  otherParentDocument->SetSubDocumentFor(otherContent, nullptr);
+  ourParentDocument->SetSubDocumentFor(ourContent, otherChildDocument);
+  otherParentDocument->SetSubDocumentFor(otherContent, ourChildDocument);
+
+  ourWindow->SetFrameElementInternal(otherFrameElement);
+  otherWindow->SetFrameElementInternal(ourFrameElement);
+
+  RefPtr<nsFrameMessageManager> ourMessageManager = mMessageManager;
+  RefPtr<nsFrameMessageManager> otherMessageManager = aOther->mMessageManager;
+  // Swap pointers in child message managers.
+  if (mChildMessageManager) {
+    InProcessBrowserChildMessageManager* browserChild = mChildMessageManager;
+    browserChild->SetOwner(otherContent);
+    browserChild->SetChromeMessageManager(otherMessageManager);
+  }
+  if (aOther->mChildMessageManager) {
+    InProcessBrowserChildMessageManager* otherBrowserChild =
+        aOther->mChildMessageManager;
+    otherBrowserChild->SetOwner(ourContent);
+    otherBrowserChild->SetChromeMessageManager(ourMessageManager);
+  }
+  // Swap and setup things in parent message managers.
+  if (mMessageManager) {
+    mMessageManager->SetCallback(aOther);
+  }
+  if (aOther->mMessageManager) {
+    aOther->mMessageManager->SetCallback(this);
+  }
+  mMessageManager.swap(aOther->mMessageManager);
+
+  // Perform the actual swap of the internal refptrs. We keep a strong reference
+  // to ourselves to make sure we don't die while we overwrite our reference to
+  // ourself.
+  RefPtr<nsFrameLoader> kungFuDeathGrip(this);
+  aThisOwner->SetFrameLoader(aOther);
+  aOtherOwner->SetFrameLoader(kungFuDeathGrip);
+
+  // Drop any cached content viewers in the two session histories.
+  if (ourHistory) {
+    ourHistory->EvictLocalContentViewers();
+  }
+  if (otherHistory) {
+    otherHistory->EvictLocalContentViewers();
+  }
+
+  NS_ASSERTION(ourFrame == ourContent->GetPrimaryFrame() &&
+                   otherFrame == otherContent->GetPrimaryFrame(),
+               "changed primary frame");
+
+  ourFrameFrame->EndSwapDocShells(otherFrame);
+
+  // If the content being swapped came from windows on two screens with
+  // incompatible backing resolution (e.g. dragging a tab between windows on
+  // hi-dpi and low-dpi screens), it will have style data that is based on
+  // the wrong appUnitsPerDevPixel value. So we tell the PresShells that their
+  // backing scale factor may have changed. (Bug 822266)
+  ourFrame->PresShell()->BackingScaleFactorChanged();
+  otherFrame->PresShell()->BackingScaleFactorChanged();
+
+  // Initialize browser API if needed now that owner content has changed
+  InitializeBrowserAPI();
+  aOther->InitializeBrowserAPI();
+
+  return NS_OK;
+}
+
+void nsFrameLoader::Destroy(bool aForProcessSwitch) {
+  StartDestroy(aForProcessSwitch);
+}
+
+class nsFrameLoaderDestroyRunnable : public Runnable {
+  enum DestroyPhase {
+    // See the implementation of Run for an explanation of these phases.
+    eDestroyDocShell,
+    eWaitForUnloadMessage,
+    eDestroyComplete
+  };
+
+  RefPtr<nsFrameLoader> mFrameLoader;
+  DestroyPhase mPhase;
+
+ public:
+  explicit nsFrameLoaderDestroyRunnable(nsFrameLoader* aFrameLoader)
+      : mozilla::Runnable("nsFrameLoaderDestroyRunnable"),
+        mFrameLoader(aFrameLoader),
+        mPhase(eDestroyDocShell) {}
+
+  NS_IMETHOD Run() override;
+};
+
+void nsFrameLoader::StartDestroy(bool aForProcessSwitch) {
+  // nsFrameLoader::StartDestroy is called just before the frameloader is
+  // detached from the <browser> element. Destruction continues in phases via
+  // the nsFrameLoaderDestroyRunnable.
+
+  if (mDestroyCalled) {
+    return;
+  }
+  mDestroyCalled = true;
+
+  // Request a full tab state flush if the tab is closing.
+  //
+  // XXX If we find that we need to do Session Store cleanup for the frameloader
+  // that's going away, we should unconditionally do the flush here, but include
+  // the |aForProcessSwitch| flag in the completion notification.
+  if (!aForProcessSwitch) {
+    RequestFinalTabStateFlush();
+  }
+
+  // After this point, we return an error when trying to send a message using
+  // the message manager on the frame.
+  if (mMessageManager) {
+    mMessageManager->Close();
+  }
+
+  // Retain references to the <browser> element and the frameloader in case we
+  // receive any messages from the message manager on the frame. These
+  // references are dropped in DestroyComplete.
+  if (mChildMessageManager || mRemoteBrowser) {
+    mOwnerContentStrong = mOwnerContent;
+    if (auto* browserParent = GetBrowserParent()) {
+      browserParent->CacheFrameLoader(this);
+    }
+    if (mChildMessageManager) {
+      mChildMessageManager->CacheFrameLoader(this);
+    }
+  }
+
+  // If the BrowserParent has installed any event listeners on the window, this
+  // is its last chance to remove them while we're still in the document.
+  if (auto* browserParent = GetBrowserParent()) {
+    browserParent->RemoveWindowListeners();
+  }
+
+  nsCOMPtr<Document> doc;
+  bool dynamicSubframeRemoval = false;
+  if (mOwnerContent) {
+    doc = mOwnerContent->OwnerDoc();
+    dynamicSubframeRemoval = !aForProcessSwitch &&
+                             mPendingBrowsingContext->IsSubframe() &&
+                             !doc->InUnlinkOrDeletion();
+    doc->SetSubDocumentFor(mOwnerContent, nullptr);
+    MaybeUpdatePrimaryBrowserParent(eBrowserParentRemoved);
+
+    nsCOMPtr<nsFrameLoaderOwner> owner = do_QueryInterface(mOwnerContent);
+    owner->FrameLoaderDestroying(this);
+    SetOwnerContent(nullptr);
+  }
+
+  // Seems like this is a dynamic frame removal.
+  if (dynamicSubframeRemoval) {
+    BrowsingContext* browsingContext = GetExtantBrowsingContext();
+    if (browsingContext) {
+      RefPtr<ChildSHistory> childSHistory =
+          browsingContext->Top()->GetChildSessionHistory();
+      if (childSHistory) {
+        if (mozilla::SessionHistoryInParent()) {
+          uint32_t addedEntries = 0;
+          browsingContext->PreOrderWalk([&addedEntries](BrowsingContext* aBC) {
+            // The initial load doesn't increase history length.
+            addedEntries += aBC->GetHistoryEntryCount() - 1;
+          });
+
+          nsID changeID = {};
+          if (addedEntries > 0) {
+            ChildSHistory* shistory =
+                browsingContext->Top()->GetChildSessionHistory();
+            if (shistory) {
+              changeID = shistory->AddPendingHistoryChange(0, -addedEntries);
+            }
+          }
+          browsingContext->RemoveFromSessionHistory(changeID);
+        } else {
+          AutoTArray<nsID, 16> ids({browsingContext->GetHistoryID()});
+          childSHistory->LegacySHistory()->RemoveEntries(
+              ids, childSHistory->Index());
+        }
+      }
+    }
+  }
+
+  // Let the tree owner know we're gone.
+  if (mIsTopLevelContent) {
+    if (GetDocShell()) {
+      nsCOMPtr<nsIDocShellTreeItem> parentItem;
+      GetDocShell()->GetInProcessParent(getter_AddRefs(parentItem));
+      nsCOMPtr<nsIDocShellTreeOwner> owner = do_GetInterface(parentItem);
+      if (owner) {
+        owner->ContentShellRemoved(GetDocShell());
+      }
+    }
+  }
+
+  // Let our window know that we are gone
+  if (GetDocShell()) {
+    nsCOMPtr<nsPIDOMWindowOuter> win_private(GetDocShell()->GetWindow());
+    if (win_private) {
+      win_private->SetFrameElementInternal(nullptr);
+    }
+  }
+
+  nsCOMPtr<nsIRunnable> destroyRunnable =
+      new nsFrameLoaderDestroyRunnable(this);
+  if (mNeedsAsyncDestroy || !doc ||
+      NS_FAILED(doc->FinalizeFrameLoader(this, destroyRunnable))) {
+    NS_DispatchToCurrentThread(destroyRunnable);
+  }
+}
+
+nsresult nsFrameLoaderDestroyRunnable::Run() {
+  switch (mPhase) {
+    case eDestroyDocShell:
+      mFrameLoader->DestroyDocShell();
+
+      // In the out-of-process case, BrowserParent will eventually call
+      // DestroyComplete once it receives a __delete__ message from the child.
+      // In the in-process case, or if the BrowserParent was already destroyed,
+      // we dispatch a series of runnables to ensure that DestroyComplete gets
+      // called at the right time. The frame loader is kept alive by
+      // mFrameLoader during this time.
+      if (!mFrameLoader->GetRemoteBrowser() ||
+          !mFrameLoader->GetRemoteBrowser()->CanRecv()) {
+        // When the docshell is destroyed, NotifyWindowIDDestroyed is called to
+        // asynchronously notify {outer,inner}-window-destroyed via a runnable.
+        // We don't want DestroyComplete to run until after those runnables have
+        // run. Since we're enqueueing ourselves after the window-destroyed
+        // runnables are enqueued, we're guaranteed to run after.
+        mPhase = eWaitForUnloadMessage;
+        NS_DispatchToCurrentThread(this);
+      }
+      break;
+
+    case eWaitForUnloadMessage:
+      // The *-window-destroyed observers have finished running at this
+      // point. However, it's possible that a *-window-destroyed observer might
+      // have sent a message using the message manager. These messages might not
+      // have been processed yet. So we enqueue ourselves again to ensure that
+      // DestroyComplete runs after all messages sent by *-window-destroyed
+      // observers have been processed.
+      mPhase = eDestroyComplete;
+      NS_DispatchToCurrentThread(this);
+      break;
+
+    case eDestroyComplete:
+      // Now that all messages sent by unload listeners and window destroyed
+      // observers have been processed, we disconnect the message manager and
+      // finish destruction.
+      mFrameLoader->DestroyComplete();
+      break;
+  }
+
+  return NS_OK;
+}
+
+void nsFrameLoader::DestroyDocShell() {
+  // This code runs after the frameloader has been detached from the <browser>
+  // element. We postpone this work because we may not be allowed to run
+  // script at that time.
+
+  // Ask the BrowserChild to fire the frame script "unload" event, destroy its
+  // docshell, and finally destroy the PBrowser actor. This eventually leads to
+  // nsFrameLoader::DestroyComplete being called.
+  if (mRemoteBrowser) {
+    mRemoteBrowser->DestroyStart();
+  }
+
+  // Fire the "unload" event if we're in-process.
+  if (mChildMessageManager) {
+    mChildMessageManager->FireUnloadEvent();
+  }
+
+  if (mSessionStoreChild) {
+    mSessionStoreChild->Stop();
+    mSessionStoreChild = nullptr;
+  }
+
+  // Destroy the docshell.
+  if (GetDocShell()) {
+    GetDocShell()->Destroy();
+  }
+
+  if (!mWillChangeProcess && mPendingBrowsingContext &&
+      mPendingBrowsingContext->EverAttached()) {
+    mPendingBrowsingContext->Detach();
+  }
+
+  mPendingBrowsingContext = nullptr;
+  mDocShell = nullptr;
+
+  if (mChildMessageManager) {
+    // Stop handling events in the in-process frame script.
+    mChildMessageManager->DisconnectEventListeners();
+  }
+}
+
+void nsFrameLoader::DestroyComplete() {
+  // We get here, as part of StartDestroy, after the docshell has been destroyed
+  // and all message manager messages sent during docshell destruction have been
+  // dispatched.  We also get here if the child process crashes. In the latter
+  // case, StartDestroy might not have been called.
+
+  // Drop the strong references created in StartDestroy.
+  if (mChildMessageManager || mRemoteBrowser) {
+    mOwnerContentStrong = nullptr;
+    if (auto* browserParent = GetBrowserParent()) {
+      browserParent->CacheFrameLoader(nullptr);
+    }
+    if (mChildMessageManager) {
+      mChildMessageManager->CacheFrameLoader(nullptr);
+    }
+  }
+
+  // Call BrowserParent::Destroy if we haven't already (in case of a crash).
+  if (mRemoteBrowser) {
+    mRemoteBrowser->DestroyComplete();
+    mRemoteBrowser = nullptr;
+  }
+
+  if (mMessageManager) {
+    mMessageManager->Disconnect();
+  }
+
+  if (mChildMessageManager) {
+    mChildMessageManager->Disconnect();
+  }
+
+  mMessageManager = nullptr;
+  mChildMessageManager = nullptr;
+}
+
+void nsFrameLoader::SetOwnerContent(Element* aContent) {
+  if (mObservingOwnerContent) {
+    mObservingOwnerContent = false;
+    mOwnerContent->RemoveMutationObserver(this);
+  }
+
+  // XXXBFCache Need to update also all the non-current FrameLoaders in the
+  // owner when moving a FrameLoader.
+  // This temporary setup doesn't crash, but behaves badly with bfcached docs.
+  if (RefPtr<nsFrameLoaderOwner> owner = do_QueryObject(mOwnerContent)) {
+    owner->DetachFrameLoader(this);
+  }
+
+  mOwnerContent = aContent;
+
+  if (RefPtr<nsFrameLoaderOwner> owner = do_QueryObject(mOwnerContent)) {
+    owner->AttachFrameLoader(this);
+
+#ifdef NIGHTLY_BUILD
+    if (mozilla::BFCacheInParent() && XRE_IsParentProcess()) {
+      if (BrowsingContext* bc = GetMaybePendingBrowsingContext()) {
+        nsISHistory* shistory = bc->Canonical()->GetSessionHistory();
+        if (shistory) {
+          uint32_t count = shistory->GetCount();
+          for (uint32_t i = 0; i < count; ++i) {
+            nsCOMPtr<nsISHEntry> entry;
+            shistory->GetEntryAtIndex(i, getter_AddRefs(entry));
+            nsCOMPtr<SessionHistoryEntry> she = do_QueryInterface(entry);
+            MOZ_RELEASE_ASSERT(!she || !she->GetFrameLoader());
+          }
+        }
+      }
+    }
+#endif
+  }
+
+  if (mSessionStoreChild && mOwnerContent) {
+    // mOwnerContent will only be null when the frame loader is being destroyed,
+    // so the session store listener will be destroyed along with it.
+    // XXX(farre): This probably needs to update the cache. See bug 1698497.
+    mSessionStoreChild->SetOwnerContent(mOwnerContent);
+  }
+
+  if (RefPtr<BrowsingContext> browsingContext = GetExtantBrowsingContext()) {
+    browsingContext->SetEmbedderElement(mOwnerContent);
+  }
+
+  if (mSessionStoreChild) {
+    // UpdateEventTargets will requery its browser contexts for event
+    // targets, so this call needs to happen after the call to
+    // SetEmbedderElement above.
+    mSessionStoreChild->UpdateEventTargets();
+  }
+
+  AutoJSAPI jsapi;
+  jsapi.Init();
+
+  JS::Rooted<JSObject*> wrapper(jsapi.cx(), GetWrapper());
+  if (wrapper) {
+    JSAutoRealm ar(jsapi.cx(), wrapper);
+    IgnoredErrorResult rv;
+    UpdateReflectorGlobal(jsapi.cx(), wrapper, rv);
+    Unused << NS_WARN_IF(rv.Failed());
+  }
+}
+
+bool nsFrameLoader::OwnerIsMozBrowserFrame() {
+  nsCOMPtr<nsIMozBrowserFrame> browserFrame = do_QueryInterface(mOwnerContent);
+  return browserFrame ? browserFrame->GetReallyIsBrowser() : false;
+}
+
+nsIContent* nsFrameLoader::GetParentObject() const { return mOwnerContent; }
+
+void nsFrameLoader::AssertSafeToInit() {
+  MOZ_DIAGNOSTIC_ASSERT(nsContentUtils::IsSafeToRunScript() ||
+                            mOwnerContent->OwnerDoc()->IsStaticDocument(),
+                        "FrameLoader should never be initialized during "
+                        "document update or reflow!");
+}
+
+nsresult nsFrameLoader::MaybeCreateDocShell() {
+  if (GetDocShell()) {
+    return NS_OK;
+  }
+  if (IsRemoteFrame()) {
+    return NS_OK;
+  }
+  NS_ENSURE_STATE(!mDestroyCalled);
+
+  AssertSafeToInit();
+
+  // Get our parent docshell off the document of mOwnerContent
+  // XXXbz this is such a total hack.... We really need to have a
+  // better setup for doing this.
+  Document* doc = mOwnerContent->OwnerDoc();
+
+  MOZ_RELEASE_ASSERT(!doc->IsResourceDoc(), "We shouldn't even exist");
+
+  // If we've already tried to initialize and failed, don't try again.
+  if (mInitialized) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+  mInitialized = true;
+
+  // Check if the document still has a window since it is possible for an
+  // iframe to be inserted and cause the creation of the docshell in a
+  // partially unloaded document (see Bug 1305237 comment 127).
+  if (!doc->IsStaticDocument() &&
+      (!doc->GetWindow() || !mOwnerContent->IsInComposedDoc())) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  if (!doc->IsActive()) {
+    // Don't allow subframe loads in non-active documents.
+    // (See bug 610571 comment 5.)
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  RefPtr<nsDocShell> parentDocShell = nsDocShell::Cast(doc->GetDocShell());
+  if (NS_WARN_IF(!parentDocShell)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  if (doc->GetWindowContext()->IsDiscarded() ||
+      parentDocShell->GetBrowsingContext()->IsDiscarded()) {
+    // Don't allow subframe loads in discarded contexts.
+    // (see bug 1652085, bug 1656854)
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  if (!EnsureBrowsingContextAttached()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  mPendingBrowsingContext->SetEmbedderElement(mOwnerContent);
+
+  // nsDocShell::Create will attach itself to the passed browsing
+  // context inside of nsDocShell::Create
+  RefPtr<nsDocShell> docShell = nsDocShell::Create(mPendingBrowsingContext);
+  NS_ENSURE_TRUE(docShell, NS_ERROR_FAILURE);
+  mDocShell = docShell;
+
+  mPendingBrowsingContext->Embed();
+
+  InvokeBrowsingContextReadyCallback();
+
+  mIsTopLevelContent = mPendingBrowsingContext->IsTopContent();
+
+  if (mIsTopLevelContent) {
+    // Manually add ourselves to our parent's docshell, as BrowsingContext won't
+    // have done this for us.
+    //
+    // XXX(nika): Consider removing the DocShellTree in the future, for
+    // consistency between local and remote frames..
+    parentDocShell->AddChild(docShell);
+  }
+
+  // Now that we are part of the DocShellTree, attach our DocShell to our
+  // parent's TreeOwner.
+  nsCOMPtr<nsIDocShellTreeOwner> parentTreeOwner;
+  parentDocShell->GetTreeOwner(getter_AddRefs(parentTreeOwner));
+  AddTreeItemToTreeOwner(docShell, parentTreeOwner);
+
+  // Make sure all nsDocShells have links back to the content element in the
+  // nearest enclosing chrome shell.
+  RefPtr<EventTarget> chromeEventHandler;
+  bool parentIsContent = parentDocShell->GetBrowsingContext()->IsContent();
+  if (parentIsContent) {
+    // Our parent shell is a content shell. Get the chrome event handler from it
+    // and use that for our shell as well.
+    parentDocShell->GetChromeEventHandler(getter_AddRefs(chromeEventHandler));
+  } else {
+    // Our parent shell is a chrome shell. It is therefore our nearest enclosing
+    // chrome shell.
+    chromeEventHandler = mOwnerContent;
+  }
+
+  docShell->SetChromeEventHandler(chromeEventHandler);
+
+  // This is nasty, this code (the docShell->GetWindow() below)
+  // *must* come *after* the above call to
+  // docShell->SetChromeEventHandler() for the global window to get
+  // the right chrome event handler.
+
+  // Tell the window about the frame that hosts it.
+  nsCOMPtr<nsPIDOMWindowOuter> newWindow = docShell->GetWindow();
+  if (NS_WARN_IF(!newWindow)) {
+    // Do not call Destroy() here. See bug 472312.
+    NS_WARNING("Something wrong when creating the docshell for a frameloader!");
+    return NS_ERROR_FAILURE;
+  }
+
+  newWindow->SetFrameElementInternal(mOwnerContent);
+
+  // Allow scripts to close the docshell if specified.
+  if (mOwnerContent->IsXULElement(nsGkAtoms::browser) &&
+      mOwnerContent->AttrValueIs(kNameSpaceID_None,
+                                 nsGkAtoms::allowscriptstoclose,
+                                 nsGkAtoms::_true, eCaseMatters)) {
+    nsGlobalWindowOuter::Cast(newWindow)->AllowScriptsToClose();
+  }
+
+  if (!docShell->Initialize()) {
+    // Do not call Destroy() here. See bug 472312.
+    NS_WARNING("Something wrong when creating the docshell for a frameloader!");
+    return NS_ERROR_FAILURE;
+  }
+
+  NS_ENSURE_STATE(mOwnerContent);
+
+  // If we are an in-process browser, we want to set up our session history.
+  if (mIsTopLevelContent && mOwnerContent->IsXULElement(nsGkAtoms::browser) &&
+      !mOwnerContent->HasAttr(kNameSpaceID_None, nsGkAtoms::disablehistory)) {
+    // XXX(nika): Set this up more explicitly?
+    mPendingBrowsingContext->InitSessionHistory();
+  }
+
+  // Apply sandbox flags even if our owner is not an iframe, as this copies
+  // flags from our owning content's owning document.
+  // Note: ApplySandboxFlags should be called after docShell->SetIsFrame
+  // because we need to get the correct presentation URL in ApplySandboxFlags.
+  uint32_t sandboxFlags = 0;
+  HTMLIFrameElement* iframe = HTMLIFrameElement::FromNode(mOwnerContent);
+  if (iframe) {
+    sandboxFlags = iframe->GetSandboxFlags();
+  }
+  ApplySandboxFlags(sandboxFlags);
+  MOZ_ALWAYS_SUCCEEDS(mPendingBrowsingContext->SetInitialSandboxFlags(
+      mPendingBrowsingContext->GetSandboxFlags()));
+
+  if (OwnerIsMozBrowserFrame()) {
+    // For inproc frames, set the docshell properties.
+    nsAutoString name;
+    if (mOwnerContent->GetAttr(kNameSpaceID_None, nsGkAtoms::name, name)) {
+      docShell->SetName(name);
+    }
+  }
+
+  ReallyLoadFrameScripts();
+  InitializeBrowserAPI();
+
+  // Previously we would forcibly create the initial about:blank document for
+  // in-process content frames from a frame script which eagerly loaded in
+  // every tab.  This lead to other frontend components growing dependencies on
+  // the initial about:blank document being created eagerly.  See bug 1471327
+  // for details.
+  //
+  // We also eagerly create the initial about:blank document for remote loads
+  // separately when initializing BrowserChild.
+  if (mIsTopLevelContent &&
+      mPendingBrowsingContext->GetMessageManagerGroup() == u"browsers"_ns) {
+    Unused << mDocShell->GetDocument();
+  }
+
+  return NS_OK;
+}
+
+void nsFrameLoader::GetURL(nsString& aURI, nsIPrincipal** aTriggeringPrincipal,
+                           nsIContentSecurityPolicy** aCsp) {
+  aURI.Truncate();
+  // Within this function we default to using the NodePrincipal as the
+  // triggeringPrincipal and the CSP of the document.
+  // Expanded Principals however override the CSP of the document, hence
+  // if frame->GetSrcTriggeringPrincipal() returns a valid principal, we
+  // have to query the CSP from that Principal.
+  nsCOMPtr<nsIPrincipal> triggeringPrincipal = mOwnerContent->NodePrincipal();
+  nsCOMPtr<nsIContentSecurityPolicy> csp = mOwnerContent->GetCsp();
+
+  if (mOwnerContent->IsHTMLElement(nsGkAtoms::object)) {
+    mOwnerContent->GetAttr(kNameSpaceID_None, nsGkAtoms::data, aURI);
+  } else {
+    mOwnerContent->GetAttr(kNameSpaceID_None, nsGkAtoms::src, aURI);
+    if (RefPtr<nsGenericHTMLFrameElement> frame =
+            do_QueryObject(mOwnerContent)) {
+      nsCOMPtr<nsIPrincipal> srcPrincipal = frame->GetSrcTriggeringPrincipal();
+      if (srcPrincipal) {
+        triggeringPrincipal = srcPrincipal;
+        nsCOMPtr<nsIExpandedPrincipal> ep =
+            do_QueryInterface(triggeringPrincipal);
+        if (ep) {
+          csp = ep->GetCsp();
+        }
+      }
+    }
+  }
+  triggeringPrincipal.forget(aTriggeringPrincipal);
+  csp.forget(aCsp);
+}
+
+nsresult nsFrameLoader::CheckForRecursiveLoad(nsIURI* aURI) {
+  MOZ_ASSERT(!IsRemoteFrame(),
+             "Shouldn't call CheckForRecursiveLoad on remote frames.");
+
+  mDepthTooGreat = false;
+  RefPtr<BrowsingContext> parentBC(
+      mOwnerContent->OwnerDoc()->GetBrowsingContext());
+  NS_ENSURE_STATE(parentBC);
+
+  if (!parentBC->IsContent()) {
+    return NS_OK;
+  }
+
+  // Bug 8065: Don't exceed some maximum depth in content frames
+  // (MAX_DEPTH_CONTENT_FRAMES)
+  int32_t depth = 0;
+  for (BrowsingContext* bc = parentBC; bc; bc = bc->GetParent()) {
+    ++depth;
+    if (depth >= MAX_DEPTH_CONTENT_FRAMES) {
+      mDepthTooGreat = true;
+      NS_WARNING("Too many nested content frames so giving up");
+
+      return NS_ERROR_UNEXPECTED;  // Too deep, give up!  (silently?)
+    }
+  }
+
+  return NS_OK;
+}
+
+nsresult nsFrameLoader::GetWindowDimensions(nsIntRect& aRect) {
+  if (!mOwnerContent) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Need to get outer window position here
+  Document* doc = mOwnerContent->GetComposedDoc();
+  if (!doc) {
+    return NS_ERROR_FAILURE;
+  }
+
+  MOZ_RELEASE_ASSERT(!doc->IsResourceDoc(), "We shouldn't even exist");
+
+  nsCOMPtr<nsPIDOMWindowOuter> win = doc->GetWindow();
+  if (!win) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsCOMPtr<nsIDocShellTreeItem> parentAsItem(win->GetDocShell());
+  if (!parentAsItem) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsCOMPtr<nsIDocShellTreeOwner> parentOwner;
+  if (NS_FAILED(parentAsItem->GetTreeOwner(getter_AddRefs(parentOwner))) ||
+      !parentOwner) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsCOMPtr<nsIBaseWindow> treeOwnerAsWin(do_GetInterface(parentOwner));
+  treeOwnerAsWin->GetPosition(&aRect.x, &aRect.y);
+  treeOwnerAsWin->GetSize(&aRect.width, &aRect.height);
+  return NS_OK;
+}
+
+nsresult nsFrameLoader::UpdatePositionAndSize(nsSubDocumentFrame* aIFrame) {
+  if (IsRemoteFrame()) {
+    if (mRemoteBrowser) {
+      ScreenIntSize size = aIFrame->GetSubdocumentSize();
+      // If we were not able to show remote frame before, we should probably
+      // retry now to send correct showInfo.
+      if (!mRemoteBrowserShown) {
+        ShowRemoteFrame(size, aIFrame);
+      }
+      nsIntRect dimensions;
+      NS_ENSURE_SUCCESS(GetWindowDimensions(dimensions), NS_ERROR_FAILURE);
+      mLazySize = size;
+      mRemoteBrowser->UpdateDimensions(dimensions, size);
+    }
+    return NS_OK;
+  }
+  UpdateBaseWindowPositionAndSize(aIFrame);
+  return NS_OK;
+}
+
+void nsFrameLoader::PropagateIsUnderHiddenEmbedderElement(
+    bool aIsUnderHiddenEmbedderElement) {
+  bool isUnderHiddenEmbedderElement = true;
+  if (Document* ownerDoc = GetOwnerDoc()) {
+    if (PresShell* presShell = ownerDoc->GetPresShell()) {
+      isUnderHiddenEmbedderElement = presShell->IsUnderHiddenEmbedderElement();
+    }
+  }
+
+  isUnderHiddenEmbedderElement |= aIsUnderHiddenEmbedderElement;
+
+  BrowsingContext* browsingContext = GetExtantBrowsingContext();
+  if (browsingContext && browsingContext->IsUnderHiddenEmbedderElement() !=
+                             isUnderHiddenEmbedderElement) {
+    Unused << browsingContext->SetIsUnderHiddenEmbedderElement(
+        isUnderHiddenEmbedderElement);
+  }
+}
+
+void nsFrameLoader::UpdateRemoteStyle(
+    mozilla::StyleImageRendering aImageRendering) {
+  MOZ_DIAGNOSTIC_ASSERT(IsRemoteFrame());
+
+  if (auto* browserBridgeChild = GetBrowserBridgeChild()) {
+    browserBridgeChild->SendUpdateRemoteStyle(aImageRendering);
+  }
+}
+
+void nsFrameLoader::UpdateBaseWindowPositionAndSize(
+    nsSubDocumentFrame* aIFrame) {
+  nsCOMPtr<nsIBaseWindow> baseWindow = GetDocShell(IgnoreErrors());
+
+  // resize the sub document
+  if (baseWindow) {
+    int32_t x = 0;
+    int32_t y = 0;
+
+    AutoWeakFrame weakFrame(aIFrame);
+
+    baseWindow->GetPosition(&x, &y);
+
+    if (!weakFrame.IsAlive()) {
+      // GetPosition() killed us
+      return;
+    }
+
+    ScreenIntSize size = aIFrame->GetSubdocumentSize();
+    mLazySize = size;
+
+    baseWindow->SetPositionAndSize(x, y, size.width, size.height,
+                                   nsIBaseWindow::eDelayResize);
+  }
+}
+
+uint32_t nsFrameLoader::LazyWidth() const {
+  uint32_t lazyWidth = mLazySize.width;
+
+  nsIFrame* frame = GetPrimaryFrameOfOwningContent();
+  if (frame) {
+    lazyWidth = frame->PresContext()->DevPixelsToIntCSSPixels(lazyWidth);
+  }
+
+  return lazyWidth;
+}
+
+uint32_t nsFrameLoader::LazyHeight() const {
+  uint32_t lazyHeight = mLazySize.height;
+
+  nsIFrame* frame = GetPrimaryFrameOfOwningContent();
+  if (frame) {
+    lazyHeight = frame->PresContext()->DevPixelsToIntCSSPixels(lazyHeight);
+  }
+
+  return lazyHeight;
+}
+
+bool nsFrameLoader::EnsureRemoteBrowser() {
+  MOZ_ASSERT(IsRemoteFrame());
+  return mRemoteBrowser || TryRemoteBrowser();
+}
+
+bool nsFrameLoader::TryRemoteBrowserInternal() {
+  NS_ASSERTION(!mRemoteBrowser,
+               "TryRemoteBrowser called with a remote browser already?");
+  MOZ_DIAGNOSTIC_ASSERT(XRE_IsParentProcess(),
+                        "Remote subframes should only be created using the "
+                        "`CanonicalBrowsingContext::ChangeRemoteness` API");
+
+  AssertSafeToInit();
+
+  if (!mOwnerContent) {
+    return false;
+  }
+
+  // XXXsmaug Per spec (2014/08/21) frameloader should not work in case the
+  //         element isn't in document, only in shadow dom, but that will change
+  //         https://www.w3.org/Bugs/Public/show_bug.cgi?id=26365#c0
+  RefPtr<Document> doc = mOwnerContent->GetComposedDoc();
+  if (!doc) {
+    return false;
+  }
+
+  MOZ_RELEASE_ASSERT(!doc->IsResourceDoc(), "We shouldn't even exist");
+
+  // Graphics initialization code relies on having a frame for the
+  // remote browser case, as we can be inside a popup, which is a different
+  // widget.
+  //
+  // FIXME: Ideally this should be unconditional, but we skip if for <iframe
+  // mozbrowser> because the old RDM ui depends on current behavior, and the
+  // mozbrowser frame code is scheduled for deletion, see bug 1574886.
+  if (!OwnerIsMozBrowserFrame() && !mOwnerContent->GetPrimaryFrame()) {
+    doc->FlushPendingNotifications(FlushType::Frames);
+  }
+
+  // The flush could have initialized us.
+  if (mRemoteBrowser) {
+    return true;
+  }
+
+  // If we've already tried to initialize and failed, don't try again.
+  if (mInitialized) {
+    return false;
+  }
+  mInitialized = true;
+
+  // Ensure the world hasn't changed that much as a result of that.
+  if (!mOwnerContent || mOwnerContent->OwnerDoc() != doc ||
+      !mOwnerContent->IsInComposedDoc()) {
+    return false;
+  }
+
+  if (RefPtr<nsFrameLoaderOwner> flo = do_QueryObject(mOwnerContent)) {
+    RefPtr<nsFrameLoader> fl = flo->GetFrameLoader();
+    if (fl != this) {
+      MOZ_ASSERT_UNREACHABLE(
+          "Got TryRemoteBrowserInternal but mOwnerContent already has a "
+          "different frameloader?");
+      return false;
+    }
+  }
+
+  if (!doc->IsActive()) {
+    // Don't allow subframe loads in non-active documents.
+    // (See bug 610571 comment 5.)
+    return false;
+  }
+
+  nsCOMPtr<nsPIDOMWindowOuter> parentWin = doc->GetWindow();
+  if (!parentWin) {
+    return false;
+  }
+
+  nsCOMPtr<nsIDocShell> parentDocShell = parentWin->GetDocShell();
+  if (!parentDocShell) {
+    return false;
+  }
+
+  if (!EnsureBrowsingContextAttached()) {
+    return false;
+  }
+
+  if (mPendingBrowsingContext->IsTop()) {
+    mPendingBrowsingContext->InitSessionHistory();
+  }
+
+  // <iframe mozbrowser> gets to skip these checks.
+  // iframes for JS plugins also get to skip these checks. We control the URL
+  // that gets loaded, but the load is triggered from the document containing
+  // the plugin.
+  // out of process iframes also get to skip this check.
+  if (!OwnerIsMozBrowserFrame() && !XRE_IsContentProcess()) {
+    if (parentDocShell->ItemType() != nsIDocShellTreeItem::typeChrome) {
+      // Allow three exceptions to this rule :
+      // - about:addons so it can load remote extension options pages
+      // - about:preferences (in Thunderbird only) so it can load remote
+      //     extension options pages for FileLink providers
+      // - DevTools webext panels if DevTools is loaded in a content frame
+      // - DevTools Network Monitor, which uses content frame for HTML request
+      // previews
+      // - Chrome mochitests can also do this.
+      //
+      // Note that the new frame's message manager will not be a child of the
+      // chrome window message manager, and, the values of window.top and
+      // window.parent will be different than they would be for a non-remote
+      // frame.
+      nsIURI* parentURI = parentWin->GetDocumentURI();
+      if (!parentURI) {
+        return false;
+      }
+
+      nsAutoCString specIgnoringRef;
+      if (NS_FAILED(parentURI->GetSpecIgnoringRef(specIgnoringRef))) {
+        return false;
+      }
+
+      const bool allowed = [&] {
+        const nsLiteralCString kAllowedURIs[] = {
+            "about:addons"_ns,
+            "chrome://mozapps/content/extensions/aboutaddons.html"_ns,
+#ifdef MOZ_THUNDERBIRD
+            "about:3pane"_ns,
+            "about:message"_ns,
+            "about:preferences"_ns,
+#endif
+            "chrome://browser/content/webext-panels.xhtml"_ns,
+            "chrome://devtools/content/netmonitor/index.html"_ns,
+            "chrome://devtools/content/webconsole/index.html"_ns,
+        };
+
+        for (const auto& allowedURI : kAllowedURIs) {
+          if (specIgnoringRef.Equals(allowedURI)) {
+            return true;
+          }
+        }
+
+        if (xpc::IsInAutomation() &&
+            StringBeginsWith(specIgnoringRef,
+                             "chrome://mochitests/content/chrome/"_ns)) {
+          return true;
+        }
+        return false;
+      }();
+
+      if (!allowed) {
+        NS_WARNING(
+            nsPrintfCString("Forbidden remote frame from content docshell %s",
+                            specIgnoringRef.get())
+                .get());
+        return false;
+      }
+    }
+
+    if (!mOwnerContent->IsXULElement()) {
+      return false;
+    }
+
+    if (!mOwnerContent->AttrValueIs(kNameSpaceID_None, nsGkAtoms::type,
+                                    nsGkAtoms::content, eIgnoreCase)) {
+      return false;
+    }
+  }
+
+  uint32_t chromeFlags = 0;
+  nsCOMPtr<nsIDocShellTreeOwner> parentOwner;
+  if (NS_FAILED(parentDocShell->GetTreeOwner(getter_AddRefs(parentOwner))) ||
+      !parentOwner) {
+    return false;
+  }
+  nsCOMPtr<nsIAppWindow> window(do_GetInterface(parentOwner));
+  if (window && NS_FAILED(window->GetChromeFlags(&chromeFlags))) {
+    return false;
+  }
+
+  AUTO_PROFILER_LABEL("nsFrameLoader::TryRemoteBrowser:Create", OTHER);
+
+  MutableTabContext context;
+  nsresult rv = GetNewTabContext(&context);
+  NS_ENSURE_SUCCESS(rv, false);
+
+  RefPtr<Element> ownerElement = mOwnerContent;
+
+  RefPtr<BrowserParent> nextRemoteBrowser =
+      mOpenWindowInfo ? mOpenWindowInfo->GetNextRemoteBrowser() : nullptr;
+  if (nextRemoteBrowser) {
+    mRemoteBrowser = new BrowserHost(nextRemoteBrowser);
+    if (nextRemoteBrowser->GetOwnerElement()) {
+      MOZ_ASSERT_UNREACHABLE("Shouldn't have an owner element before");
+      return false;
+    }
+    nextRemoteBrowser->SetOwnerElement(ownerElement);
+  } else {
+    RefPtr<ContentParent> contentParent;
+    if (mChildID != 0) {
+      ContentProcessManager* cpm = ContentProcessManager::GetSingleton();
+      if (!cpm) {
+        return false;
+      }
+      contentParent = cpm->GetContentProcessById(ContentParentId(mChildID));
+    }
+    mRemoteBrowser =
+        ContentParent::CreateBrowser(context, ownerElement, mRemoteType,
+                                     mPendingBrowsingContext, contentParent);
+  }
+  if (!mRemoteBrowser) {
+    return false;
+  }
+
+  MOZ_DIAGNOSTIC_ASSERT(mPendingBrowsingContext ==
+                        mRemoteBrowser->GetBrowsingContext());
+
+  mRemoteBrowser->GetBrowsingContext()->Embed();
+  InvokeBrowsingContextReadyCallback();
+
+  // Grab the reference to the actor
+  RefPtr<BrowserParent> browserParent = GetBrowserParent();
+
+  MOZ_ASSERT(browserParent->CanSend(), "BrowserParent cannot send?");
+
+  // We no longer need the remoteType attribute on the frame element.
+  // The remoteType can be queried by asking the message manager instead.
+  ownerElement->UnsetAttr(kNameSpaceID_None, nsGkAtoms::RemoteType, false);
+
+  // Now that browserParent is set, we can initialize graphics
+  browserParent->InitRendering();
+
+  MaybeUpdatePrimaryBrowserParent(eBrowserParentChanged);
+
+  mChildID = browserParent->Manager()->ChildID();
+
+  nsCOMPtr<nsIDocShellTreeItem> rootItem;
+  parentDocShell->GetInProcessRootTreeItem(getter_AddRefs(rootItem));
+  nsCOMPtr<nsPIDOMWindowOuter> rootWin = rootItem->GetWindow();
+  nsCOMPtr<nsIDOMChromeWindow> rootChromeWin = do_QueryInterface(rootWin);
+
+  if (rootChromeWin) {
+    nsCOMPtr<nsIBrowserDOMWindow> browserDOMWin;
+    rootChromeWin->GetBrowserDOMWindow(getter_AddRefs(browserDOMWin));
+    browserParent->SetBrowserDOMWindow(browserDOMWin);
+  }
+
+  // For xul:browsers, update some settings based on attributes:
+  if (mOwnerContent->IsXULElement()) {
+    // Send down the name of the browser through browserParent if it is set.
+    nsAutoString frameName;
+    mOwnerContent->GetAttr(kNameSpaceID_None, nsGkAtoms::name, frameName);
+    if (nsContentUtils::IsOverridingWindowName(frameName)) {
+      MOZ_ALWAYS_SUCCEEDS(mPendingBrowsingContext->SetName(frameName));
+    }
+    // Allow scripts to close the window if the browser specified so:
+    if (mOwnerContent->AttrValueIs(kNameSpaceID_None,
+                                   nsGkAtoms::allowscriptstoclose,
+                                   nsGkAtoms::_true, eCaseMatters)) {
+      Unused << browserParent->SendAllowScriptsToClose();
+    }
+  }
+
+  ReallyLoadFrameScripts();
+  InitializeBrowserAPI();
+
+  return true;
+}
+
+bool nsFrameLoader::TryRemoteBrowser() {
+  // Creating remote browsers may result in creating new processes, but during
+  // parent shutdown that would add just noise, so better bail out.
+  if (AppShutdown::IsInOrBeyond(ShutdownPhase::AppShutdownConfirmed)) {
+    return false;
+  }
+
+  // Try to create the internal remote browser.
+  if (TryRemoteBrowserInternal()) {
+    return true;
+  }
+
+  // Check if we should report a browser-crashed error because the browser
+  // failed to start.
+  if (XRE_IsParentProcess() && mOwnerContent && mOwnerContent->IsXULElement()) {
+    MaybeNotifyCrashed(nullptr, ContentParentId(), nullptr);
+  }
+
+  return false;
+}
+
+nsIFrame* nsFrameLoader::GetPrimaryFrameOfOwningContent() const {
+  return mOwnerContent ? mOwnerContent->GetPrimaryFrame() : nullptr;
+}
+
+Document* nsFrameLoader::GetOwnerDoc() const {
+  return mOwnerContent ? mOwnerContent->OwnerDoc() : nullptr;
+}
+
+bool nsFrameLoader::IsRemoteFrame() {
+  if (mIsRemoteFrame) {
+    MOZ_ASSERT(!GetDocShell(), "Found a remote frame with a DocShell");
+    return true;
+  }
+  return false;
+}
+
+RemoteBrowser* nsFrameLoader::GetRemoteBrowser() const {
+  return mRemoteBrowser;
+}
+
+BrowserParent* nsFrameLoader::GetBrowserParent() const {
+  if (!mRemoteBrowser) {
+    return nullptr;
+  }
+  RefPtr<BrowserHost> browserHost = mRemoteBrowser->AsBrowserHost();
+  if (!browserHost) {
+    return nullptr;
+  }
+  return browserHost->GetActor();
+}
+
+BrowserBridgeChild* nsFrameLoader::GetBrowserBridgeChild() const {
+  if (!mRemoteBrowser) {
+    return nullptr;
+  }
+  RefPtr<BrowserBridgeHost> browserBridgeHost =
+      mRemoteBrowser->AsBrowserBridgeHost();
+  if (!browserBridgeHost) {
+    return nullptr;
+  }
+  return browserBridgeHost->GetActor();
+}
+
+mozilla::layers::LayersId nsFrameLoader::GetLayersId() const {
+  MOZ_ASSERT(mIsRemoteFrame);
+  return mRemoteBrowser->GetLayersId();
+}
+
+nsresult nsFrameLoader::DoRemoteStaticClone(nsFrameLoader* aStaticCloneOf,
+                                            nsIPrintSettings* aPrintSettings) {
+  MOZ_ASSERT(aStaticCloneOf->IsRemoteFrame());
+  MOZ_ASSERT(aPrintSettings);
+  auto* cc = ContentChild::GetSingleton();
+  if (!cc) {
+    MOZ_DIAGNOSTIC_ASSERT(XRE_IsParentProcess());
+    // TODO: Could possibly be implemented without too much effort.
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  BrowsingContext* bcToClone = aStaticCloneOf->GetBrowsingContext();
+  if (NS_WARN_IF(!bcToClone)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  BrowsingContext* bc = GetBrowsingContext();
+  MOZ_DIAGNOSTIC_ASSERT(bc);
+  nsCOMPtr<nsIPrintSettingsService> printSettingsSvc =
+      do_GetService("@mozilla.org/gfx/printsettings-service;1");
+  if (NS_WARN_IF(!printSettingsSvc)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  embedding::PrintData printData;
+  nsresult rv =
+      printSettingsSvc->SerializeToPrintData(aPrintSettings, &printData);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  cc->SendCloneDocumentTreeInto(bcToClone, bc, printData);
+  return NS_OK;
+}
+
+nsresult nsFrameLoader::FinishStaticClone(
+    nsFrameLoader* aStaticCloneOf, nsIPrintSettings* aPrintSettings,
+    bool* aOutHasInProcessPrintCallbacks) {
+  MOZ_DIAGNOSTIC_ASSERT(
+      !nsContentUtils::IsSafeToRunScript(),
+      "A script blocker should be on the stack while FinishStaticClone is run");
+
+  // NOTE: We don't check `aStaticCloneOf->IsDead()` here, as the nsFrameLoader
+  // which we're a static clone of may be in the process of being destroyed. It
+  // won't be fully destroyed when `FinishStaticClone` is called, as a script
+  // blocker on our caller's stack is preventing it from becoming finalized.
+  //
+  // This is quite fragile, but is quite difficult to work around without
+  // getting print-preview to stop re-cloning and replacing the previewed
+  // document when changing layout.
+  if (NS_WARN_IF(IsDead())) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  if (aStaticCloneOf->IsRemoteFrame()) {
+    return DoRemoteStaticClone(aStaticCloneOf, aPrintSettings);
+  }
+
+  nsIDocShell* origDocShell = aStaticCloneOf->GetDocShell();
+  NS_ENSURE_STATE(origDocShell);
+
+  nsCOMPtr<Document> doc = origDocShell->GetDocument();
+  NS_ENSURE_STATE(doc);
+
+  MaybeCreateDocShell();
+  RefPtr<nsDocShell> docShell = GetDocShell();
+  NS_ENSURE_STATE(docShell);
+
+  nsCOMPtr<Document> kungFuDeathGrip = docShell->GetDocument();
+  Unused << kungFuDeathGrip;
+
+  nsCOMPtr<nsIContentViewer> viewer;
+  docShell->GetContentViewer(getter_AddRefs(viewer));
+  NS_ENSURE_STATE(viewer);
+
+  nsCOMPtr<Document> clonedDoc = doc->CreateStaticClone(
+      docShell, viewer, aPrintSettings, aOutHasInProcessPrintCallbacks);
+
+  return NS_OK;
+}
+
+bool nsFrameLoader::DoLoadMessageManagerScript(const nsAString& aURL,
+                                               bool aRunInGlobalScope) {
+  if (auto* browserParent = GetBrowserParent()) {
+    return browserParent->SendLoadRemoteScript(aURL, aRunInGlobalScope);
+  }
+  RefPtr<InProcessBrowserChildMessageManager> browserChild =
+      GetBrowserChildMessageManager();
+  if (browserChild) {
+    browserChild->LoadFrameScript(aURL, aRunInGlobalScope);
+  }
+  return true;
+}
+
+class nsAsyncMessageToChild : public nsSameProcessAsyncMessageBase,
+                              public Runnable {
+ public:
+  explicit nsAsyncMessageToChild(nsFrameLoader* aFrameLoader)
+      : nsSameProcessAsyncMessageBase(),
+        mozilla::Runnable("nsAsyncMessageToChild"),
+        mFrameLoader(aFrameLoader) {}
+
+  NS_IMETHOD Run() override {
+    InProcessBrowserChildMessageManager* browserChild =
+        mFrameLoader->mChildMessageManager;
+    // Since bug 1126089, messages can arrive even when the docShell is
+    // destroyed. Here we make sure that those messages are not delivered.
+    if (browserChild && browserChild->GetInnerManager() &&
+        mFrameLoader->GetExistingDocShell()) {
+      JS::Rooted<JSObject*> kungFuDeathGrip(dom::RootingCx(),
+                                            browserChild->GetWrapper());
+      ReceiveMessage(static_cast<EventTarget*>(browserChild), mFrameLoader,
+                     browserChild->GetInnerManager());
+    }
+    return NS_OK;
+  }
+  RefPtr<nsFrameLoader> mFrameLoader;
+};
+
+nsresult nsFrameLoader::DoSendAsyncMessage(const nsAString& aMessage,
+                                           StructuredCloneData& aData) {
+  auto* browserParent = GetBrowserParent();
+  if (browserParent) {
+    ClonedMessageData data;
+    if (!BuildClonedMessageData(aData, data)) {
+      MOZ_CRASH();
+      return NS_ERROR_DOM_DATA_CLONE_ERR;
+    }
+    if (browserParent->SendAsyncMessage(aMessage, data)) {
+      return NS_OK;
+    } else {
+      return NS_ERROR_UNEXPECTED;
+    }
+  }
+
+  if (mChildMessageManager) {
+    RefPtr<nsAsyncMessageToChild> ev = new nsAsyncMessageToChild(this);
+    nsresult rv = ev->Init(aMessage, aData);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+    rv = NS_DispatchToCurrentThread(ev);
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+    return rv;
+  }
+
+  // We don't have any targets to send our asynchronous message to.
+  return NS_ERROR_UNEXPECTED;
+}
+
+already_AddRefed<MessageSender> nsFrameLoader::GetMessageManager() {
+  EnsureMessageManager();
+  return do_AddRef(mMessageManager);
+}
+
+nsresult nsFrameLoader::EnsureMessageManager() {
+  NS_ENSURE_STATE(mOwnerContent);
+
+  if (mMessageManager) {
+    return NS_OK;
+  }
+
+  if (!mIsTopLevelContent && !OwnerIsMozBrowserFrame() && !IsRemoteFrame() &&
+      !(mOwnerContent->IsXULElement() &&
+        mOwnerContent->AttrValueIs(kNameSpaceID_None,
+                                   nsGkAtoms::forcemessagemanager,
+                                   nsGkAtoms::_true, eCaseMatters))) {
+    return NS_OK;
+  }
+
+  RefPtr<nsGlobalWindowOuter> window =
+      nsGlobalWindowOuter::Cast(GetOwnerDoc()->GetWindow());
+  RefPtr<ChromeMessageBroadcaster> parentManager;
+
+  if (window && window->IsChromeWindow()) {
+    nsAutoString messagemanagergroup;
+    if (mOwnerContent->IsXULElement() &&
+        mOwnerContent->GetAttr(kNameSpaceID_None,
+                               nsGkAtoms::messagemanagergroup,
+                               messagemanagergroup)) {
+      parentManager = window->GetGroupMessageManager(messagemanagergroup);
+    }
+
+    if (!parentManager) {
+      parentManager = window->GetMessageManager();
+    }
+  } else {
+    parentManager = nsFrameMessageManager::GetGlobalMessageManager();
+  }
+
+  mMessageManager = new ChromeMessageSender(parentManager);
+  if (!IsRemoteFrame()) {
+    nsresult rv = MaybeCreateDocShell();
+    if (NS_FAILED(rv)) {
+      return rv;
+    }
+    MOZ_ASSERT(GetDocShell(),
+               "MaybeCreateDocShell succeeded, but null docShell");
+    if (!GetDocShell()) {
+      return NS_ERROR_FAILURE;
+    }
+    mChildMessageManager = InProcessBrowserChildMessageManager::Create(
+        GetDocShell(), mOwnerContent, mMessageManager);
+    NS_ENSURE_TRUE(mChildMessageManager, NS_ERROR_UNEXPECTED);
+
+    // Set up session store
+    if (StaticPrefs::browser_sessionstore_platform_collection_AtStartup()) {
+      if (XRE_IsParentProcess() && mIsTopLevelContent) {
+        mSessionStoreChild = SessionStoreChild::GetOrCreate(
+            GetExtantBrowsingContext(), mOwnerContent);
+      }
+    }
+  }
+  return NS_OK;
+}
+
+nsresult nsFrameLoader::ReallyLoadFrameScripts() {
+  nsresult rv = EnsureMessageManager();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  if (mMessageManager) {
+    mMessageManager->InitWithCallback(this);
+  }
+  return NS_OK;
+}
+
+already_AddRefed<Element> nsFrameLoader::GetOwnerElement() {
+  return do_AddRef(mOwnerContent);
+}
+
+void nsFrameLoader::SetDetachedSubdocFrame(nsIFrame* aDetachedFrame,
+                                           Document* aContainerDoc) {
+  mDetachedSubdocFrame = aDetachedFrame;
+  mContainerDocWhileDetached = aContainerDoc;
+}
+
+nsIFrame* nsFrameLoader::GetDetachedSubdocFrame(
+    Document** aContainerDoc) const {
+  NS_IF_ADDREF(*aContainerDoc = mContainerDocWhileDetached);
+  return mDetachedSubdocFrame.GetFrame();
+}
+
+void nsFrameLoader::ApplySandboxFlags(uint32_t sandboxFlags) {
+  // If our BrowsingContext doesn't exist yet, it means we haven't been
+  // initialized yet. This method will be called again once we're initialized
+  // from MaybeCreateDocShell. <iframe> BrowsingContexts are never created as
+  // initially remote, so we don't need to worry about updating sandbox flags
+  // for an uninitialized initially-remote iframe.
+  BrowsingContext* context = GetExtantBrowsingContext();
+  if (!context) {
+    MOZ_ASSERT(!IsRemoteFrame(),
+               "cannot apply sandbox flags to an uninitialized "
+               "initially-remote frame");
+    return;
+  }
+
+  uint32_t parentSandboxFlags = mOwnerContent->OwnerDoc()->GetSandboxFlags();
+
+  // The child can only add restrictions, never remove them.
+  sandboxFlags |= parentSandboxFlags;
+
+  MOZ_ALWAYS_SUCCEEDS(context->SetSandboxFlags(sandboxFlags));
+}
+
+/* virtual */
+void nsFrameLoader::AttributeChanged(mozilla::dom::Element* aElement,
+                                     int32_t aNameSpaceID, nsAtom* aAttribute,
+                                     int32_t aModType,
+                                     const nsAttrValue* aOldValue) {
+  MOZ_ASSERT(mObservingOwnerContent);
+
+  if (aElement != mOwnerContent) {
+    return;
+  }
+
+  if (aNameSpaceID != kNameSpaceID_None ||
+      (aAttribute != TypeAttrName(aElement) &&
+       aAttribute != nsGkAtoms::primary)) {
+    return;
+  }
+
+  // Note: This logic duplicates a lot of logic in
+  // MaybeCreateDocshell.  We should fix that.
+
+  // Notify our enclosing chrome that our type has changed.  We only do this
+  // if our parent is chrome, since in all other cases we're random content
+  // subframes and the treeowner shouldn't worry about us.
+  if (!GetDocShell()) {
+    MaybeUpdatePrimaryBrowserParent(eBrowserParentChanged);
+    return;
+  }
+
+  nsCOMPtr<nsIDocShellTreeItem> parentItem;
+  GetDocShell()->GetInProcessParent(getter_AddRefs(parentItem));
+  if (!parentItem) {
+    return;
+  }
+
+  if (parentItem->ItemType() != nsIDocShellTreeItem::typeChrome) {
+    return;
+  }
+
+  nsCOMPtr<nsIDocShellTreeOwner> parentTreeOwner;
+  parentItem->GetTreeOwner(getter_AddRefs(parentTreeOwner));
+  if (!parentTreeOwner) {
+    return;
+  }
+
+  bool is_primary = aElement->AttrValueIs(kNameSpaceID_None, nsGkAtoms::primary,
+                                          nsGkAtoms::_true, eIgnoreCase);
+
+  // when a content panel is no longer primary, hide any open popups it may have
+  if (!is_primary) {
+    nsXULPopupManager* pm = nsXULPopupManager::GetInstance();
+    if (pm) {
+      pm->HidePopupsInDocShell(GetDocShell());
+    }
+  }
+
+  parentTreeOwner->ContentShellRemoved(GetDocShell());
+  if (aElement->AttrValueIs(kNameSpaceID_None, TypeAttrName(aElement),
+                            nsGkAtoms::content, eIgnoreCase)) {
+    parentTreeOwner->ContentShellAdded(GetDocShell(), is_primary);
+  }
+}
+
+void nsFrameLoader::RequestUpdatePosition(ErrorResult& aRv) {
+  if (auto* browserParent = GetBrowserParent()) {
+    nsresult rv = browserParent->UpdatePosition();
+
+    if (NS_FAILED(rv)) {
+      aRv.Throw(rv);
+    }
+  }
+}
+
+SessionStoreParent* nsFrameLoader::GetSessionStoreParent() {
+  MOZ_DIAGNOSTIC_ASSERT(XRE_IsParentProcess());
+  if (mSessionStoreChild) {
+    return static_cast<SessionStoreParent*>(
+        InProcessChild::ParentActorFor(mSessionStoreChild));
+  }
+
+  if (BrowserParent* browserParent = GetBrowserParent()) {
+    return static_cast<SessionStoreParent*>(
+        SingleManagedOrNull(browserParent->ManagedPSessionStoreParent()));
+  }
+
+  return nullptr;
+}
+
+already_AddRefed<Promise> nsFrameLoader::RequestTabStateFlush(
+    ErrorResult& aRv) {
+  MOZ_DIAGNOSTIC_ASSERT(XRE_IsParentProcess());
+  Document* ownerDoc = GetOwnerDoc();
+  if (!ownerDoc) {
+    aRv.ThrowNotSupportedError("No owner document");
+    return nullptr;
+  }
+
+  RefPtr<Promise> promise = Promise::Create(ownerDoc->GetOwnerGlobal(), aRv);
+  if (aRv.Failed()) {
+    return nullptr;
+  }
+
+  BrowsingContext* browsingContext = GetExtantBrowsingContext();
+  if (!browsingContext) {
+    promise->MaybeResolveWithUndefined();
+    return promise.forget();
+  }
+
+  SessionStoreParent* sessionStoreParent = GetSessionStoreParent();
+  if (!sessionStoreParent) {
+    promise->MaybeResolveWithUndefined();
+    return promise.forget();
+  }
+
+  sessionStoreParent->FlushAllSessionStoreChildren(
+      [promise]() { promise->MaybeResolveWithUndefined(); });
+
+  return promise.forget();
+}
+
+void nsFrameLoader::RequestFinalTabStateFlush() {
+  BrowsingContext* context = GetExtantBrowsingContext();
+  if (!context || !context->IsTop() || context->Canonical()->IsReplaced()) {
+    return;
+  }
+
+  RefPtr<CanonicalBrowsingContext> canonical = context->Canonical();
+  RefPtr<WindowGlobalParent> wgp = canonical->GetCurrentWindowGlobal();
+  RefPtr<Element> embedder = context->GetEmbedderElement();
+
+  RefPtr<SessionStoreParent> sessionStoreParent = GetSessionStoreParent();
+  if (!sessionStoreParent) {
+    canonical->ClearPermanentKey();
+    if (wgp) {
+      wgp->NotifySessionStoreUpdatesComplete(embedder);
+    }
+
+    return;
+  }
+
+  sessionStoreParent->FinalFlushAllSessionStoreChildren(
+      [canonical, wgp, embedder]() {
+        if (canonical) {
+          canonical->ClearPermanentKey();
+        }
+        if (wgp) {
+          wgp->NotifySessionStoreUpdatesComplete(embedder);
+        }
+      });
+}
+
+void nsFrameLoader::RequestEpochUpdate(uint32_t aEpoch) {
+  BrowsingContext* context = GetExtantBrowsingContext();
+  if (context) {
+    BrowsingContext* top = context->Top();
+    Unused << top->SetSessionStoreEpoch(aEpoch);
+  }
+}
+
+void nsFrameLoader::RequestSHistoryUpdate() {
+  if (mSessionStoreChild) {
+    mSessionStoreChild->UpdateSHistoryChanges();
+    return;
+  }
+
+  // If remote browsing (e10s), handle this with the BrowserParent.
+  if (auto* browserParent = GetBrowserParent()) {
+    Unused << browserParent->SendUpdateSHistory();
+  }
+}
+
+already_AddRefed<Promise> nsFrameLoader::PrintPreview(
+    nsIPrintSettings* aPrintSettings, BrowsingContext* aSourceBrowsingContext,
+    ErrorResult& aRv) {
+  auto* ownerDoc = GetOwnerDoc();
+  if (!ownerDoc) {
+    aRv.ThrowNotSupportedError("No owner document");
+    return nullptr;
+  }
+  RefPtr<Promise> promise = Promise::Create(ownerDoc->GetOwnerGlobal(), aRv);
+  if (!promise) {
+    return nullptr;
+  }
+
+#ifndef NS_PRINTING
+  promise->MaybeRejectWithNotSupportedError("Build does not support printing");
+  return promise.forget();
+#else
+  auto resolve = [promise](PrintPreviewResultInfo aInfo) {
+    using Orientation = dom::PrintPreviewOrientation;
+    if (aInfo.sheetCount() > 0) {
+      PrintPreviewSuccessInfo info;
+      info.mSheetCount = aInfo.sheetCount();
+      info.mTotalPageCount = aInfo.totalPageCount();
+      info.mHasSelection = aInfo.hasSelection();
+      info.mHasSelfSelection = aInfo.hasSelfSelection();
+      info.mIsEmpty = aInfo.isEmpty();
+      if (aInfo.printLandscape()) {
+        info.mOrientation = aInfo.printLandscape().value()
+                                ? Orientation::Landscape
+                                : Orientation::Portrait;
+      } else {
+        MOZ_ASSERT(info.mOrientation == Orientation::Unspecified);
+      }
+      if (aInfo.pageWidth()) {
+        info.mPageWidth = aInfo.pageWidth().value();
+      }
+      if (aInfo.pageHeight()) {
+        info.mPageHeight = aInfo.pageHeight().value();
+      }
+
+      promise->MaybeResolve(info);
+    } else {
+      promise->MaybeRejectWithUnknownError("Print preview failed");
+    }
+  };
+
+  if (auto* browserParent = GetBrowserParent()) {
+    nsCOMPtr<nsIPrintSettingsService> printSettingsSvc =
+        do_GetService("@mozilla.org/gfx/printsettings-service;1");
+    if (!printSettingsSvc) {
+      promise->MaybeRejectWithNotSupportedError("No nsIPrintSettingsService");
+      return promise.forget();
+    }
+
+    embedding::PrintData printData;
+    nsresult rv =
+        printSettingsSvc->SerializeToPrintData(aPrintSettings, &printData);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      promise->MaybeReject(ErrorResult(rv));
+      return promise.forget();
+    }
+
+    browserParent->SendPrintPreview(printData, aSourceBrowsingContext)
+        ->Then(
+            GetMainThreadSerialEventTarget(), __func__, std::move(resolve),
+            [promise](const mozilla::ipc::ResponseRejectReason) {
+              promise->MaybeRejectWithUnknownError("Print preview IPC failed");
+            });
+
+    return promise.forget();
+  }
+
+  RefPtr<nsGlobalWindowOuter> sourceWindow;
+  if (aSourceBrowsingContext) {
+    sourceWindow =
+        nsGlobalWindowOuter::Cast(aSourceBrowsingContext->GetDOMWindow());
+  } else {
+    nsDocShell* ourDocshell = GetExistingDocShell();
+    if (NS_WARN_IF(!ourDocshell)) {
+      promise->MaybeRejectWithNotSupportedError("No print preview docShell");
+      return promise.forget();
+    }
+    sourceWindow = nsGlobalWindowOuter::Cast(ourDocshell->GetWindow());
+  }
+  if (NS_WARN_IF(!sourceWindow)) {
+    promise->MaybeRejectWithNotSupportedError("No print preview source window");
+    return promise.forget();
+  }
+
+  nsCOMPtr<nsIDocShell> docShellToCloneInto = nullptr;
+  if (aSourceBrowsingContext) {
+    // We're going to call `Print()` below on a window that is not our own,
+    // which happens when we are creating a new print preview document instead
+    // of just applying a settings change to the existing PP document.  In this
+    // case we need to explicitly pass our docShell as the docShell to clone
+    // into.
+    docShellToCloneInto = GetExistingDocShell();
+    if (NS_WARN_IF(!docShellToCloneInto)) {
+      promise->MaybeRejectWithNotSupportedError("No print preview docShell");
+      return promise.forget();
+    }
+
+    // We need to make sure we're displayed so that the view tree ends up right.
+    RefPtr<BrowsingContext> bc = docShellToCloneInto->GetBrowsingContext();
+    if (NS_WARN_IF(!bc)) {
+      promise->MaybeRejectWithNotSupportedError(
+          "No print preview browsing context");
+      return promise.forget();
+    }
+
+    RefPtr<Element> embedder = bc->GetEmbedderElement();
+    if (NS_WARN_IF(!embedder)) {
+      promise->MaybeRejectWithNotSupportedError(
+          "Trying to clone into a frameloader with no element?");
+      return promise.forget();
+    }
+
+    nsIFrame* frame = embedder->GetPrimaryFrame(FlushType::Frames);
+    if (NS_WARN_IF(!frame)) {
+      promise->MaybeRejectWithNotSupportedError("Frame is not being displayed");
+      return promise.forget();
+    }
+  }
+
+  // Unfortunately we can't pass `resolve` directly here because IPDL, for now,
+  // unfortunately generates slightly different parameter types for functions
+  // taking PrintPreviewResultInfo in PBrowserParent vs. PBrowserChild.
+  ErrorResult rv;
+  sourceWindow->Print(
+      aPrintSettings,
+      /* aRemotePrintJob = */ nullptr,
+      /* aListener = */ nullptr, docShellToCloneInto,
+      nsGlobalWindowOuter::IsPreview::Yes,
+      nsGlobalWindowOuter::IsForWindowDotPrint::No,
+      [resolve](const PrintPreviewResultInfo& aInfo) { resolve(aInfo); }, rv);
+  if (NS_WARN_IF(rv.Failed())) {
+    promise->MaybeReject(std::move(rv));
+  }
+
+  return promise.forget();
+#endif
+}
+
+void nsFrameLoader::ExitPrintPreview() {
+#ifdef NS_PRINTING
+  if (auto* browserParent = GetBrowserParent()) {
+    Unused << browserParent->SendExitPrintPreview();
+    return;
+  }
+  if (NS_WARN_IF(!GetExistingDocShell())) {
+    return;
+  }
+  nsCOMPtr<nsIWebBrowserPrint> webBrowserPrint =
+      do_GetInterface(ToSupports(GetExistingDocShell()->GetWindow()));
+  if (NS_WARN_IF(!webBrowserPrint)) {
+    return;
+  }
+  webBrowserPrint->ExitPrintPreview();
+#endif
+}
+
+already_AddRefed<nsIRemoteTab> nsFrameLoader::GetRemoteTab() {
+  if (!mRemoteBrowser) {
+    return nullptr;
+  }
+  if (auto* browserHost = mRemoteBrowser->AsBrowserHost()) {
+    return do_AddRef(browserHost);
+  }
+  return nullptr;
+}
+
+already_AddRefed<nsILoadContext> nsFrameLoader::GetLoadContext() {
+  return do_AddRef(GetBrowsingContext());
+}
+
+BrowsingContext* nsFrameLoader::GetBrowsingContext() {
+  if (!mInitialized) {
+    if (IsRemoteFrame()) {
+      Unused << EnsureRemoteBrowser();
+    } else if (mOwnerContent) {
+      Unused << MaybeCreateDocShell();
+    }
+  }
+  MOZ_ASSERT(mInitialized);
+  return GetExtantBrowsingContext();
+}
+
+BrowsingContext* nsFrameLoader::GetExtantBrowsingContext() {
+  if (!mPendingBrowsingContext) {
+    // If mPendingBrowsingContext is null then the frame loader is being
+    // destroyed (nsFrameLoader::DestroyDocShell was called), so return null
+    // here in that case.
+    return nullptr;
+  }
+
+  if (!mInitialized || !mPendingBrowsingContext->EverAttached()) {
+    // Don't return the pending BrowsingContext until this nsFrameLoader has
+    // been initialized, and the BC was attached.
+    return nullptr;
+  }
+
+  return mPendingBrowsingContext;
+}
+
+void nsFrameLoader::InitializeBrowserAPI() {
+  if (!OwnerIsMozBrowserFrame()) {
+    return;
+  }
+
+  nsresult rv = EnsureMessageManager();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return;
+  }
+  mMessageManager->LoadFrameScript(
+      u"chrome://global/content/BrowserElementChild.js"_ns,
+      /* allowDelayedLoad = */ true,
+      /* aRunInGlobalScope */ true, IgnoreErrors());
+
+  nsCOMPtr<nsIMozBrowserFrame> browserFrame = do_QueryInterface(mOwnerContent);
+  if (browserFrame) {
+    browserFrame->InitializeBrowserAPI();
+  }
+}
+
+void nsFrameLoader::DestroyBrowserFrameScripts() {
+  if (!OwnerIsMozBrowserFrame()) {
+    return;
+  }
+  nsCOMPtr<nsIMozBrowserFrame> browserFrame = do_QueryInterface(mOwnerContent);
+  if (browserFrame) {
+    browserFrame->DestroyBrowserFrameScripts();
+  }
+}
+
+void nsFrameLoader::StartPersistence(
+    BrowsingContext* aContext, nsIWebBrowserPersistDocumentReceiver* aRecv,
+    ErrorResult& aRv) {
+  MOZ_ASSERT(aRecv);
+  RefPtr<BrowsingContext> context = aContext ? aContext : GetBrowsingContext();
+
+  if (!context || !context->IsInSubtreeOf(GetBrowsingContext())) {
+    aRecv->OnError(NS_ERROR_NO_CONTENT);
+    return;
+  }
+
+  if (!context->GetDocShell() && XRE_IsParentProcess()) {
+    CanonicalBrowsingContext* canonical =
+        CanonicalBrowsingContext::Cast(context);
+    if (!canonical->GetCurrentWindowGlobal()) {
+      aRecv->OnError(NS_ERROR_NO_CONTENT);
+      return;
+    }
+    RefPtr<BrowserParent> browserParent =
+        canonical->GetCurrentWindowGlobal()->GetBrowserParent();
+    browserParent->StartPersistence(canonical, aRecv, aRv);
+    return;
+  }
+
+  nsCOMPtr<Document> foundDoc = context->GetDocument();
+
+  if (!foundDoc) {
+    aRecv->OnError(NS_ERROR_NO_CONTENT);
+  } else {
+    nsCOMPtr<nsIWebBrowserPersistDocument> pdoc =
+        new mozilla::WebBrowserPersistLocalDocument(foundDoc);
+    aRecv->OnDocumentReady(pdoc);
+  }
+}
+
+void nsFrameLoader::MaybeUpdatePrimaryBrowserParent(
+    BrowserParentChange aChange) {
+  if (!mOwnerContent || !mRemoteBrowser) {
+    return;
+  }
+
+  RefPtr<BrowserHost> browserHost = mRemoteBrowser->AsBrowserHost();
+  if (!browserHost) {
+    return;
+  }
+
+  nsCOMPtr<nsIDocShell> docShell = mOwnerContent->OwnerDoc()->GetDocShell();
+  if (!docShell) {
+    return;
+  }
+
+  BrowsingContext* browsingContext = docShell->GetBrowsingContext();
+  if (!browsingContext->IsChrome()) {
+    return;
+  }
+
+  nsCOMPtr<nsIDocShellTreeOwner> parentTreeOwner;
+  docShell->GetTreeOwner(getter_AddRefs(parentTreeOwner));
+  if (!parentTreeOwner) {
+    return;
+  }
+
+  if (!mObservingOwnerContent) {
+    mOwnerContent->AddMutationObserver(this);
+    mObservingOwnerContent = true;
+  }
+
+  parentTreeOwner->RemoteTabRemoved(browserHost);
+  if (aChange == eBrowserParentChanged) {
+    bool isPrimary = mOwnerContent->AttrValueIs(
+        kNameSpaceID_None, nsGkAtoms::primary, nsGkAtoms::_true, eIgnoreCase);
+    parentTreeOwner->RemoteTabAdded(browserHost, isPrimary);
+  }
+}
+
+nsresult nsFrameLoader::GetNewTabContext(MutableTabContext* aTabContext,
+                                         nsIURI* aURI) {
+  nsCOMPtr<nsIDocShell> docShell = mOwnerContent->OwnerDoc()->GetDocShell();
+  nsCOMPtr<nsILoadContext> parentContext = do_QueryInterface(docShell);
+  NS_ENSURE_STATE(parentContext);
+
+  MOZ_ASSERT(mPendingBrowsingContext->EverAttached());
+
+  uint64_t chromeOuterWindowID = 0;
+
+  nsCOMPtr<nsPIWindowRoot> root =
+      nsContentUtils::GetWindowRoot(mOwnerContent->OwnerDoc());
+  if (root) {
+    nsPIDOMWindowOuter* outerWin = root->GetWindow();
+    if (outerWin) {
+      chromeOuterWindowID = outerWin->WindowID();
+    }
+  }
+
+  uint32_t maxTouchPoints = BrowserParent::GetMaxTouchPoints(mOwnerContent);
+
+  bool tabContextUpdated =
+      aTabContext->SetTabContext(chromeOuterWindowID, maxTouchPoints);
+  NS_ENSURE_STATE(tabContextUpdated);
+
+  return NS_OK;
+}
+
+nsresult nsFrameLoader::PopulateOriginContextIdsFromAttributes(
+    OriginAttributes& aAttr) {
+  // Only XUL or mozbrowser frames are allowed to set context IDs
+  uint32_t namespaceID = mOwnerContent->GetNameSpaceID();
+  if (namespaceID != kNameSpaceID_XUL && !OwnerIsMozBrowserFrame()) {
+    return NS_OK;
+  }
+
+  nsAutoString attributeValue;
+  if (aAttr.mUserContextId ==
+          nsIScriptSecurityManager::DEFAULT_USER_CONTEXT_ID &&
+      mOwnerContent->GetAttr(kNameSpaceID_None, nsGkAtoms::usercontextid,
+                             attributeValue) &&
+      !attributeValue.IsEmpty()) {
+    nsresult rv;
+    aAttr.mUserContextId = attributeValue.ToInteger(&rv);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  if (aAttr.mGeckoViewSessionContextId.IsEmpty() &&
+      mOwnerContent->GetAttr(kNameSpaceID_None,
+                             nsGkAtoms::geckoViewSessionContextId,
+                             attributeValue) &&
+      !attributeValue.IsEmpty()) {
+    // XXX: Should we check the format from `GeckoViewNavigation.jsm` here?
+    aAttr.mGeckoViewSessionContextId = attributeValue;
+  }
+
+  return NS_OK;
+}
+
+ProcessMessageManager* nsFrameLoader::GetProcessMessageManager() const {
+  if (auto* browserParent = GetBrowserParent()) {
+    return browserParent->Manager()->GetMessageManager();
+  }
+  return nullptr;
+};
+
+JSObject* nsFrameLoader::WrapObject(JSContext* cx,
+                                    JS::Handle<JSObject*> aGivenProto) {
+  JS::Rooted<JSObject*> result(cx);
+  FrameLoader_Binding::Wrap(cx, this, this, aGivenProto, &result);
+  return result;
+}
+
+void nsFrameLoader::SetWillChangeProcess() {
+  mWillChangeProcess = true;
+
+  if (IsRemoteFrame()) {
+    if (auto* browserParent = GetBrowserParent()) {
+      if (auto* bc = CanonicalBrowsingContext::Cast(mPendingBrowsingContext);
+          bc && bc->EverAttached()) {
+        bc->StartUnloadingHost(browserParent->Manager()->ChildID());
+        bc->SetCurrentBrowserParent(nullptr);
+      }
+      // OOP Browser - Go directly over Browser Parent
+      Unused << browserParent->SendWillChangeProcess();
+    } else if (auto* browserBridgeChild = GetBrowserBridgeChild()) {
+      // OOP IFrame - Through Browser Bridge Parent, set on browser child
+      Unused << browserBridgeChild->SendWillChangeProcess();
+    }
+    return;
+  }
+
+  // In process
+  RefPtr<nsDocShell> docshell = GetDocShell();
+  MOZ_ASSERT(docshell);
+  docshell->SetWillChangeProcess();
+}
+
+static mozilla::Result<bool, nsresult> DidBuildIDChange() {
+  nsresult rv;
+  nsCOMPtr<nsIFile> file;
+
+  rv = NS_GetSpecialDirectory(NS_GRE_DIR, getter_AddRefs(file));
+  MOZ_TRY(rv);
+
+  rv = file->AppendNative("platform.ini"_ns);
+  MOZ_TRY(rv);
+
+  nsCOMPtr<nsIINIParserFactory> iniFactory =
+      do_GetService("@mozilla.org/xpcom/ini-parser-factory;1", &rv);
+  MOZ_TRY(rv);
+
+  nsCOMPtr<nsIINIParser> parser;
+  rv = iniFactory->CreateINIParser(file, getter_AddRefs(parser));
+  MOZ_TRY(rv);
+
+  nsAutoCString installedBuildID;
+  rv = parser->GetString("Build"_ns, "BuildID"_ns, installedBuildID);
+  MOZ_TRY(rv);
+
+  nsDependentCString runningBuildID(PlatformBuildID());
+  return (installedBuildID != runningBuildID);
+}
+
+void nsFrameLoader::MaybeNotifyCrashed(BrowsingContext* aBrowsingContext,
+                                       ContentParentId aChildID,
+                                       mozilla::ipc::MessageChannel* aChannel) {
+  if (mTabProcessCrashFired) {
+    return;
+  }
+
+  if (mPendingBrowsingContext == aBrowsingContext) {
+    mTabProcessCrashFired = true;
+  }
+
+  // Fire the crashed observer notification.
+  nsCOMPtr<nsIObserverService> os = services::GetObserverService();
+  if (!os) {
+    return;
+  }
+
+  os->NotifyObservers(ToSupports(this), "oop-frameloader-crashed", nullptr);
+
+  // Check our owner element still references us. If it's moved, on, events
+  // don't need to be fired.
+  RefPtr<nsFrameLoaderOwner> owner = do_QueryObject(mOwnerContent);
+  if (!owner) {
+    return;
+  }
+
+  RefPtr<nsFrameLoader> currentFrameLoader = owner->GetFrameLoader();
+  if (currentFrameLoader != this) {
+    return;
+  }
+
+#if defined(MOZ_TELEMETRY_REPORTING)
+  bool sendTelemetry = false;
+#endif  // defined(MOZ_TELEMETRY_REPORTING)
+
+  // Fire the actual crashed event.
+  nsString eventName;
+  if (aChannel && !aChannel->DoBuildIDsMatch()) {
+    auto changedOrError = DidBuildIDChange();
+    if (changedOrError.isErr()) {
+      NS_WARNING("Error while checking buildid mismatch");
+      eventName = u"oop-browser-buildid-mismatch"_ns;
+    } else {
+      bool aChanged = changedOrError.unwrap();
+      if (aChanged) {
+        NS_WARNING("True build ID mismatch");
+        eventName = u"oop-browser-buildid-mismatch"_ns;
+      } else {
+        NS_WARNING("build ID mismatch false alarm");
+        eventName = u"oop-browser-crashed"_ns;
+#if defined(MOZ_TELEMETRY_REPORTING)
+        sendTelemetry = true;
+#endif  // defined(MOZ_TELEMETRY_REPORTING)
+      }
+    }
+  } else {
+    NS_WARNING("No build ID mismatch");
+    eventName = u"oop-browser-crashed"_ns;
+  }
+
+#if defined(MOZ_TELEMETRY_REPORTING)
+  if (sendTelemetry) {
+    Telemetry::ScalarAdd(
+        Telemetry::ScalarID::DOM_CONTENTPROCESS_BUILDID_MISMATCH_FALSE_POSITIVE,
+        1);
+  }
+#endif  // defined(MOZ_TELEMETRY_REPORTING)
+
+  FrameCrashedEventInit init;
+  init.mBubbles = true;
+  init.mCancelable = true;
+  if (aBrowsingContext) {
+    init.mBrowsingContextId = aBrowsingContext->Id();
+    init.mIsTopFrame = aBrowsingContext->IsTop();
+    init.mChildID = aChildID;
+  }
+
+  RefPtr<FrameCrashedEvent> event = FrameCrashedEvent::Constructor(
+      mOwnerContent->OwnerDoc(), eventName, init);
+  event->SetTrusted(true);
+
+  RefPtr<Element> ownerContent = mOwnerContent;
+  EventDispatcher::DispatchDOMEvent(ownerContent, nullptr, event, nullptr,
+                                    nullptr);
+}
+
+bool nsFrameLoader::EnsureBrowsingContextAttached() {
+  nsresult rv;
+
+  Document* parentDoc = mOwnerContent->OwnerDoc();
+  MOZ_ASSERT(parentDoc);
+  BrowsingContext* parentContext = parentDoc->GetBrowsingContext();
+  MOZ_ASSERT(parentContext);
+
+  // Inherit the `use` flags from our parent BrowsingContext.
+  bool usePrivateBrowsing = parentContext->UsePrivateBrowsing();
+  bool useRemoteSubframes = parentContext->UseRemoteSubframes();
+  bool useRemoteTabs = parentContext->UseRemoteTabs();
+
+  // Determine the exact OriginAttributes which should be used for our
+  // BrowsingContext. This will be used to initialize OriginAttributes if the
+  // BrowsingContext has not already been created.
+  OriginAttributes attrs;
+  if (mPendingBrowsingContext->IsContent()) {
+    if (mPendingBrowsingContext->GetParent()) {
+      MOZ_ASSERT(mPendingBrowsingContext->GetParent() == parentContext);
+      parentContext->GetOriginAttributes(attrs);
+    }
+
+    // Inherit the `mFirstPartyDomain` flag from our parent document's result
+    // principal, if it was set.
+    if (parentContext->IsContent() &&
+        !parentDoc->NodePrincipal()->IsSystemPrincipal() &&
+        !OwnerIsMozBrowserFrame()) {
+      OriginAttributes docAttrs =
+          parentDoc->NodePrincipal()->OriginAttributesRef();
+      // We only want to inherit firstPartyDomain here, other attributes should
+      // be constant.
+      MOZ_ASSERT(attrs.EqualsIgnoringFPD(docAttrs));
+      attrs.mFirstPartyDomain = docAttrs.mFirstPartyDomain;
+    }
+
+    // Inherit the PrivateBrowsing flag across content/chrome boundaries.
+    attrs.SyncAttributesWithPrivateBrowsing(usePrivateBrowsing);
+
+    // A <browser> element may have overridden userContextId or
+    // geckoViewUserContextId.
+    rv = PopulateOriginContextIdsFromAttributes(attrs);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return false;
+    }
+
+    // <iframe mozbrowser> is allowed to set `mozprivatebrowsing` to
+    // force-enable private browsing.
+    if (OwnerIsMozBrowserFrame()) {
+      if (mOwnerContent->HasAttr(kNameSpaceID_None,
+                                 nsGkAtoms::mozprivatebrowsing)) {
+        attrs.SyncAttributesWithPrivateBrowsing(true);
+        usePrivateBrowsing = true;
+      }
+    }
+  }
+
+  // If we've already been attached, return.
+  if (mPendingBrowsingContext->EverAttached()) {
+    MOZ_DIAGNOSTIC_ASSERT(mPendingBrowsingContext->UsePrivateBrowsing() ==
+                          usePrivateBrowsing);
+    MOZ_DIAGNOSTIC_ASSERT(mPendingBrowsingContext->UseRemoteTabs() ==
+                          useRemoteTabs);
+    MOZ_DIAGNOSTIC_ASSERT(mPendingBrowsingContext->UseRemoteSubframes() ==
+                          useRemoteSubframes);
+    // Don't assert that our OriginAttributes match, as we could have different
+    // OriginAttributes in the case where we were opened using window.open.
+    return true;
+  }
+
+  // Initialize non-synced OriginAttributes and related fields.
+  rv = mPendingBrowsingContext->SetOriginAttributes(attrs);
+  NS_ENSURE_SUCCESS(rv, false);
+  rv = mPendingBrowsingContext->SetUsePrivateBrowsing(usePrivateBrowsing);
+  NS_ENSURE_SUCCESS(rv, false);
+  rv = mPendingBrowsingContext->SetRemoteTabs(useRemoteTabs);
+  NS_ENSURE_SUCCESS(rv, false);
+  rv = mPendingBrowsingContext->SetRemoteSubframes(useRemoteSubframes);
+  NS_ENSURE_SUCCESS(rv, false);
+
+  // Finish attaching.
+  mPendingBrowsingContext->EnsureAttached();
+  return true;
+}
+
+void nsFrameLoader::InvokeBrowsingContextReadyCallback() {
+  if (mOpenWindowInfo) {
+    if (RefPtr<nsIBrowsingContextReadyCallback> callback =
+            mOpenWindowInfo->BrowsingContextReadyCallback()) {
+      callback->BrowsingContextReady(mPendingBrowsingContext);
+    }
+  }
+}