Adding upstream version 124.0.1.upstream/124.0.1

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

18 files changed, 1650 insertions, 0 deletions

diff --git a/layout/tools/layout-debug/LayoutDebugChild.sys.mjs b/layout/tools/layout-debug/LayoutDebugChild.sys.mjs
new file mode 100644
index 0000000000..7a15e36cae
--- /dev/null
+++ b/layout/tools/layout-debug/LayoutDebugChild.sys.mjs
@@ -0,0 +1,29 @@
+/* vim: set ts=2 sw=2 sts=2 et tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+const NS_LAYOUT_DEBUGGINGTOOLS_CONTRACTID =
+  "@mozilla.org/layout-debug/layout-debuggingtools;1";
+
+export class LayoutDebugChild extends JSWindowActorChild {
+  receiveMessage(msg) {
+    if (!this._debuggingTools) {
+      this._debuggingTools = Cc[
+        NS_LAYOUT_DEBUGGINGTOOLS_CONTRACTID
+      ].createInstance(Ci.nsILayoutDebuggingTools);
+      this._debuggingTools.init(this.contentWindow);
+    }
+    switch (msg.name) {
+      case "LayoutDebug:Call":
+        let pid = Services.appinfo.processID;
+        dump(`[${pid} ${this.contentWindow.location}]\n`);
+        this._debuggingTools[msg.data.name](msg.data.arg);
+        dump("\n");
+        break;
+      default:
+        throw `unknown message ${msg.name} sent to LayoutDebugChild`;
+    }
+    return Promise.resolve(true);
+  }
+}
diff --git a/layout/tools/layout-debug/moz.build b/layout/tools/layout-debug/moz.build
new file mode 100644
index 0000000000..cc7cf90dd2
--- /dev/null
+++ b/layout/tools/layout-debug/moz.build
@@ -0,0 +1,13 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DIRS += ["src", "ui"]
+
+XPCSHELL_TESTS_MANIFESTS += ["tests/unit/xpcshell.toml"]
+
+BROWSER_CHROME_MANIFESTS += ["tests/browser/browser.toml"]
+
+FINAL_TARGET_FILES.actors += ["LayoutDebugChild.sys.mjs"]
diff --git a/layout/tools/layout-debug/src/components.conf b/layout/tools/layout-debug/src/components.conf
new file mode 100644
index 0000000000..07ad3d155d
--- /dev/null
+++ b/layout/tools/layout-debug/src/components.conf
@@ -0,0 +1,21 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+Classes = [
+    {
+        'cid': '{3f4c3b63-e640-4712-abbf-fff1301ceb60}',
+        'contract_ids': ['@mozilla.org/layout-debug/layout-debuggingtools;1'],
+        'type': 'nsLayoutDebuggingTools',
+        'headers': ['/layout/tools/layout-debug/src/nsLayoutDebuggingTools.h'],
+    },
+    {
+        'cid': '{a8f52633-5ecf-424a-a147-47c322f7bc2e}',
+        'contract_ids': ['@mozilla.org/commandlinehandler/general-startup;1?type=layoutdebug'],
+        'type': 'nsLayoutDebugCLH',
+        'headers': ['/layout/tools/layout-debug/src/nsLayoutDebugCLH.h'],
+        'categories': {'command-line-handler': 'm-layoutdebug'},
+    },
+]
diff --git a/layout/tools/layout-debug/src/moz.build b/layout/tools/layout-debug/src/moz.build
new file mode 100644
index 0000000000..37f9389fa3
--- /dev/null
+++ b/layout/tools/layout-debug/src/moz.build
@@ -0,0 +1,24 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+XPIDL_SOURCES += [
+    "nsILayoutDebuggingTools.idl",
+]
+
+XPIDL_MODULE = "layout_debug"
+
+UNIFIED_SOURCES += [
+    "nsLayoutDebugCLH.cpp",
+    "nsLayoutDebuggingTools.cpp",
+]
+
+XPCOM_MANIFESTS += [
+    "components.conf",
+]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+FINAL_LIBRARY = "xul"
diff --git a/layout/tools/layout-debug/src/nsILayoutDebuggingTools.idl b/layout/tools/layout-debug/src/nsILayoutDebuggingTools.idl
new file mode 100644
index 0000000000..f689734a46
--- /dev/null
+++ b/layout/tools/layout-debug/src/nsILayoutDebuggingTools.idl
@@ -0,0 +1,44 @@
+/* -*- Mode: IDL; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+// vim:cindent:tabstop=4:expandtab:shiftwidth=4:
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+interface mozIDOMWindow;
+
+/**
+ * A series of hooks into non-IDL-ized layout code to allow all the
+ * layout debugging functions to be used from chrome.
+ */
+
+[builtinclass, scriptable, uuid(f336d8d3-9721-4ad3-85d0-a7018c0a3383)]
+interface nsILayoutDebuggingTools : nsISupports
+{
+    /*
+     * Initialize debugger object to act on a docshell.
+     */
+    void init(in mozIDOMWindow win);
+
+    // Repaint the window.
+    void forceRefresh();
+
+    /* Toggle various debugging states */
+    void setReflowCounts(in boolean enabled);
+    void setPagedMode(in boolean enabled);
+
+    /* Run various tests. */
+    void dumpContent();
+    void dumpFrames();
+    void dumpFramesInCSSPixels();
+    void dumpTextRuns();
+    void dumpViews();
+    void dumpCounterManager();
+
+    void dumpStyleSheets();
+    void dumpMatchedRules();
+    void dumpComputedStyles();
+
+    void dumpReflowStats();
+};
diff --git a/layout/tools/layout-debug/src/nsLayoutDebugCLH.cpp b/layout/tools/layout-debug/src/nsLayoutDebugCLH.cpp
new file mode 100644
index 0000000000..c50f3af44a
--- /dev/null
+++ b/layout/tools/layout-debug/src/nsLayoutDebugCLH.cpp
@@ -0,0 +1,187 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+// vim:cindent:tabstop=4:expandtab:shiftwidth=4:
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsLayoutDebugCLH.h"
+#include "mozIDOMWindow.h"
+#include "nsArray.h"
+#include "nsString.h"
+#include "nsComponentManagerUtils.h"
+#include "nsCOMPtr.h"
+#include "nsIWindowWatcher.h"
+#include "nsISupportsPrimitives.h"
+#include "nsICommandLine.h"
+#include "nsIURI.h"
+#include "nsServiceManagerUtils.h"
+
+nsLayoutDebugCLH::nsLayoutDebugCLH() = default;
+
+nsLayoutDebugCLH::~nsLayoutDebugCLH() = default;
+
+NS_IMPL_ISUPPORTS(nsLayoutDebugCLH, ICOMMANDLINEHANDLER)
+
+static nsresult HandleFlagWithOptionalArgument(nsICommandLine* aCmdLine,
+                                               const nsAString& aName,
+                                               const nsAString& aDefaultValue,
+                                               nsAString& aValue,
+                                               bool& aFlagPresent) {
+  aValue.Truncate();
+  aFlagPresent = false;
+
+  nsresult rv;
+  int32_t idx;
+
+  rv = aCmdLine->FindFlag(aName, false, &idx);
+  NS_ENSURE_SUCCESS(rv, rv);
+  if (idx < 0) return NS_OK;
+
+  aFlagPresent = true;
+
+  int32_t length;
+  aCmdLine->GetLength(&length);
+
+  bool argPresent = false;
+
+  if (idx + 1 < length) {
+    rv = aCmdLine->GetArgument(idx + 1, aValue);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    if (!aValue.IsEmpty() && aValue.CharAt(0) == '-') {
+      aValue.Truncate();
+    } else {
+      argPresent = true;
+    }
+  }
+
+  if (!argPresent) {
+    aValue = aDefaultValue;
+  }
+
+  return aCmdLine->RemoveArguments(idx, idx + argPresent);
+}
+
+static nsresult HandleFlagWithOptionalArgument(nsICommandLine* aCmdLine,
+                                               const nsAString& aName,
+                                               double aDefaultValue,
+                                               double& aValue,
+                                               bool& aFlagPresent) {
+  nsresult rv;
+  nsString s;
+
+  rv =
+      HandleFlagWithOptionalArgument(aCmdLine, aName, u"0"_ns, s, aFlagPresent);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (!aFlagPresent) {
+    aValue = 0.0;
+    return NS_OK;
+  }
+
+  aValue = s.ToDouble(&rv);
+  return rv;
+}
+
+static nsresult AppendArg(nsIMutableArray* aArray, const nsAString& aString) {
+  nsCOMPtr<nsISupportsString> s =
+      do_CreateInstance(NS_SUPPORTS_STRING_CONTRACTID);
+  NS_ENSURE_TRUE(s, NS_ERROR_FAILURE);
+  s->SetData(aString);
+  return aArray->AppendElement(s);
+}
+
+NS_IMETHODIMP
+nsLayoutDebugCLH::Handle(nsICommandLine* aCmdLine) {
+  nsresult rv;
+  bool flagPresent;
+
+  nsString url;
+  bool autoclose = false;
+  double delay = 0.0;
+  bool captureProfile = false;
+  nsString profileFilename;
+  bool paged = false;
+
+  rv = HandleFlagWithOptionalArgument(aCmdLine, u"layoutdebug"_ns,
+                                      u"about:blank"_ns, url, flagPresent);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (!flagPresent) {
+    return NS_OK;
+  }
+
+  rv = HandleFlagWithOptionalArgument(aCmdLine, u"autoclose"_ns, 0.0, delay,
+                                      autoclose);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = HandleFlagWithOptionalArgument(aCmdLine, u"capture-profile"_ns,
+                                      u"profile.json"_ns, profileFilename,
+                                      captureProfile);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = aCmdLine->HandleFlag(u"paged"_ns, false, &paged);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsIMutableArray> argsArray = nsArray::Create();
+
+  nsCOMPtr<nsIURI> uri;
+  nsAutoCString resolvedSpec;
+
+  rv = aCmdLine->ResolveURI(url, getter_AddRefs(uri));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = uri->GetSpec(resolvedSpec);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = AppendArg(argsArray, NS_ConvertUTF8toUTF16(resolvedSpec));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (autoclose) {
+    nsString arg;
+    arg.AppendPrintf("autoclose=%f", delay);
+
+    rv = AppendArg(argsArray, arg);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  if (captureProfile) {
+    nsString arg;
+    arg.AppendLiteral("profile=");
+    arg.Append(profileFilename);
+
+    rv = AppendArg(argsArray, arg);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  if (paged) {
+    rv = AppendArg(argsArray, u"paged"_ns);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  nsCOMPtr<nsIWindowWatcher> wwatch =
+      do_GetService(NS_WINDOWWATCHER_CONTRACTID);
+  NS_ENSURE_TRUE(wwatch, NS_ERROR_FAILURE);
+
+  nsCOMPtr<mozIDOMWindowProxy> opened;
+  wwatch->OpenWindow(
+      nullptr, "chrome://layoutdebug/content/layoutdebug.xhtml"_ns, "_blank"_ns,
+      "chrome,dialog=no,all"_ns, argsArray, getter_AddRefs(opened));
+  aCmdLine->SetPreventDefault(true);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLayoutDebugCLH::GetHelpInfo(nsACString& aResult) {
+  aResult.AssignLiteral(
+      "  --layoutdebug [<url>] Start with Layout Debugger\n"
+      "  --autoclose [<seconds>] Automatically close the Layout Debugger once\n"
+      "                     the page has loaded, after delaying the specified\n"
+      "                     number of seconds (which defaults to 0).\n"
+      "  --capture-profile [<filename>] Capture a profile of the Layout\n"
+      "                     Debugger using the Gecko Profiler, and save the\n"
+      "                     profile to the specified file (which defaults to\n"
+      "                     profile.json).\n"
+      "  --paged Layout the page in paginated mode.\n");
+  return NS_OK;
+}
diff --git a/layout/tools/layout-debug/src/nsLayoutDebugCLH.h b/layout/tools/layout-debug/src/nsLayoutDebugCLH.h
new file mode 100644
index 0000000000..aa99bf9eff
--- /dev/null
+++ b/layout/tools/layout-debug/src/nsLayoutDebugCLH.h
@@ -0,0 +1,24 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+// vim:cindent:tabstop=4:expandtab:shiftwidth=4:
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsLayoutDebugCLH_h_
+#define nsLayoutDebugCLH_h_
+
+#include "nsICommandLineHandler.h"
+#define ICOMMANDLINEHANDLER nsICommandLineHandler
+
+class nsLayoutDebugCLH : public ICOMMANDLINEHANDLER {
+ public:
+  nsLayoutDebugCLH();
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSICOMMANDLINEHANDLER
+
+ protected:
+  virtual ~nsLayoutDebugCLH();
+};
+
+#endif /* !defined(nsLayoutDebugCLH_h_) */
diff --git a/layout/tools/layout-debug/src/nsLayoutDebuggingTools.cpp b/layout/tools/layout-debug/src/nsLayoutDebuggingTools.cpp
new file mode 100644
index 0000000000..05ad47356d
--- /dev/null
+++ b/layout/tools/layout-debug/src/nsLayoutDebuggingTools.cpp
@@ -0,0 +1,327 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+// vim:cindent:tabstop=4:expandtab:shiftwidth=4:
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsLayoutDebuggingTools.h"
+
+#include "nsIDocShell.h"
+#include "nsPIDOMWindow.h"
+#include "nsIDocumentViewer.h"
+#include "nsIPrintSettings.h"
+#include "nsIPrintSettingsService.h"
+
+#include "nsAtom.h"
+
+#include "nsIContent.h"
+
+#include "nsCounterManager.h"
+#include "nsCSSFrameConstructor.h"
+#include "nsViewManager.h"
+#include "nsIFrame.h"
+
+#include "nsLayoutCID.h"
+
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/PresShell.h"
+
+using namespace mozilla;
+using mozilla::dom::Document;
+
+static already_AddRefed<nsIDocumentViewer> doc_viewer(nsIDocShell* aDocShell) {
+  if (!aDocShell) return nullptr;
+  nsCOMPtr<nsIDocumentViewer> viewer;
+  aDocShell->GetDocViewer(getter_AddRefs(viewer));
+  return viewer.forget();
+}
+
+static PresShell* GetPresShell(nsIDocShell* aDocShell) {
+  nsCOMPtr<nsIDocumentViewer> viewer = doc_viewer(aDocShell);
+  if (!viewer) return nullptr;
+  return viewer->GetPresShell();
+}
+
+static nsViewManager* view_manager(nsIDocShell* aDocShell) {
+  PresShell* presShell = GetPresShell(aDocShell);
+  if (!presShell) {
+    return nullptr;
+  }
+  return presShell->GetViewManager();
+}
+
+#ifdef DEBUG
+static already_AddRefed<Document> document(nsIDocShell* aDocShell) {
+  nsCOMPtr<nsIDocumentViewer> viewer(doc_viewer(aDocShell));
+  if (!viewer) {
+    return nullptr;
+  }
+  return do_AddRef(viewer->GetDocument());
+}
+#endif
+
+nsLayoutDebuggingTools::nsLayoutDebuggingTools() { ForceRefresh(); }
+
+nsLayoutDebuggingTools::~nsLayoutDebuggingTools() = default;
+
+NS_IMPL_ISUPPORTS(nsLayoutDebuggingTools, nsILayoutDebuggingTools)
+
+NS_IMETHODIMP
+nsLayoutDebuggingTools::Init(mozIDOMWindow* aWin) {
+  if (!Preferences::GetService()) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  {
+    if (!aWin) return NS_ERROR_UNEXPECTED;
+    auto* window = nsPIDOMWindowInner::From(aWin);
+    mDocShell = window->GetDocShell();
+  }
+  NS_ENSURE_TRUE(mDocShell, NS_ERROR_UNEXPECTED);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLayoutDebuggingTools::SetReflowCounts(bool aShow) {
+  NS_ENSURE_TRUE(mDocShell, NS_ERROR_NOT_INITIALIZED);
+  if (PresShell* presShell = GetPresShell(mDocShell)) {
+#ifdef MOZ_REFLOW_PERF
+    presShell->SetPaintFrameCount(aShow);
+#else
+    printf("************************************************\n");
+    printf("Sorry, you have not built with MOZ_REFLOW_PERF=1\n");
+    printf("************************************************\n");
+#endif
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLayoutDebuggingTools::SetPagedMode(bool aPagedMode) {
+  nsCOMPtr<nsIPrintSettingsService> printSettingsService =
+      do_GetService("@mozilla.org/gfx/printsettings-service;1");
+  nsCOMPtr<nsIPrintSettings> printSettings;
+
+  printSettingsService->CreateNewPrintSettings(getter_AddRefs(printSettings));
+
+  // Use the same setup as setupPrintMode() in reftest-content.js.
+  printSettings->SetPaperWidth(5);
+  printSettings->SetPaperHeight(3);
+
+  nsIntMargin unwriteableMargin(0, 0, 0, 0);
+  printSettings->SetUnwriteableMarginInTwips(unwriteableMargin);
+
+  printSettings->SetHeaderStrLeft(u""_ns);
+  printSettings->SetHeaderStrCenter(u""_ns);
+  printSettings->SetHeaderStrRight(u""_ns);
+
+  printSettings->SetFooterStrLeft(u""_ns);
+  printSettings->SetFooterStrCenter(u""_ns);
+  printSettings->SetFooterStrRight(u""_ns);
+
+  printSettings->SetPrintBGColors(true);
+  printSettings->SetPrintBGImages(true);
+
+  nsCOMPtr<nsIDocumentViewer> docViewer(doc_viewer(mDocShell));
+  docViewer->SetPageModeForTesting(aPagedMode, printSettings);
+
+  ForceRefresh();
+  return NS_OK;
+}
+
+static void DumpContentRecur(nsIDocShell* aDocShell, FILE* out) {
+#ifdef DEBUG
+  if (nullptr != aDocShell) {
+    fprintf(out, "docshell=%p \n", static_cast<void*>(aDocShell));
+    RefPtr<Document> doc(document(aDocShell));
+    if (doc) {
+      dom::Element* root = doc->GetRootElement();
+      if (root) {
+        root->List(out);
+      }
+    } else {
+      fputs("no document\n", out);
+    }
+  }
+#endif
+}
+
+NS_IMETHODIMP
+nsLayoutDebuggingTools::DumpContent() {
+  NS_ENSURE_TRUE(mDocShell, NS_ERROR_NOT_INITIALIZED);
+  DumpContentRecur(mDocShell, stdout);
+  return NS_OK;
+}
+
+static void DumpFramesRecur(
+    nsIDocShell* aDocShell, FILE* out,
+    nsIFrame::ListFlags aFlags = nsIFrame::ListFlags()) {
+  if (aFlags.contains(nsIFrame::ListFlag::DisplayInCSSPixels)) {
+    fprintf(out, "Frame tree in CSS pixels:\n");
+  } else {
+    fprintf(out, "Frame tree in app units:\n");
+  }
+
+  fprintf(out, "docshell=%p \n", aDocShell);
+  if (PresShell* presShell = GetPresShell(aDocShell)) {
+    nsIFrame* root = presShell->GetRootFrame();
+    if (root) {
+      root->List(out, "", aFlags);
+    }
+  } else {
+    fputs("null pres shell\n", out);
+  }
+}
+
+static void DumpTextRunsRecur(nsIDocShell* aDocShell, FILE* out) {
+  fprintf(out, "Text runs:\n");
+
+  fprintf(out, "docshell=%p \n", aDocShell);
+  if (PresShell* presShell = GetPresShell(aDocShell)) {
+    nsIFrame* root = presShell->GetRootFrame();
+    if (root) {
+      root->ListTextRuns(out);
+    }
+  } else {
+    fputs("null pres shell\n", out);
+  }
+}
+
+NS_IMETHODIMP
+nsLayoutDebuggingTools::DumpFrames() {
+  NS_ENSURE_TRUE(mDocShell, NS_ERROR_NOT_INITIALIZED);
+  DumpFramesRecur(mDocShell, stdout);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLayoutDebuggingTools::DumpFramesInCSSPixels() {
+  NS_ENSURE_TRUE(mDocShell, NS_ERROR_NOT_INITIALIZED);
+  DumpFramesRecur(mDocShell, stdout, nsIFrame::ListFlag::DisplayInCSSPixels);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLayoutDebuggingTools::DumpTextRuns() {
+  NS_ENSURE_TRUE(mDocShell, NS_ERROR_NOT_INITIALIZED);
+  DumpTextRunsRecur(mDocShell, stdout);
+  return NS_OK;
+}
+
+static void DumpViewsRecur(nsIDocShell* aDocShell, FILE* out) {
+#ifdef DEBUG
+  fprintf(out, "docshell=%p \n", static_cast<void*>(aDocShell));
+  RefPtr<nsViewManager> vm(view_manager(aDocShell));
+  if (vm) {
+    nsView* root = vm->GetRootView();
+    if (root) {
+      root->List(out);
+    }
+  } else {
+    fputs("null view manager\n", out);
+  }
+#endif  // DEBUG
+}
+
+NS_IMETHODIMP
+nsLayoutDebuggingTools::DumpViews() {
+  NS_ENSURE_TRUE(mDocShell, NS_ERROR_NOT_INITIALIZED);
+  DumpViewsRecur(mDocShell, stdout);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLayoutDebuggingTools::DumpCounterManager() {
+  NS_ENSURE_TRUE(mDocShell, NS_ERROR_NOT_INITIALIZED);
+  if (PresShell* presShell = GetPresShell(mDocShell)) {
+    presShell->FrameConstructor()->GetContainStyleScopeManager().DumpCounters();
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLayoutDebuggingTools::DumpStyleSheets() {
+  NS_ENSURE_TRUE(mDocShell, NS_ERROR_NOT_INITIALIZED);
+#if defined(DEBUG) || defined(MOZ_LAYOUT_DEBUGGER)
+  FILE* out = stdout;
+  if (PresShell* presShell = GetPresShell(mDocShell)) {
+    presShell->ListStyleSheets(out);
+  } else {
+    fputs("null pres shell\n", out);
+  }
+#endif
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsLayoutDebuggingTools::DumpMatchedRules() {
+  NS_ENSURE_TRUE(mDocShell, NS_ERROR_NOT_INITIALIZED);
+  FILE* out = stdout;
+  if (PresShell* presShell = GetPresShell(mDocShell)) {
+    nsIFrame* root = presShell->GetRootFrame();
+    if (root) {
+      root->ListWithMatchedRules(out);
+    }
+  } else {
+    fputs("null pres shell\n", out);
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLayoutDebuggingTools::DumpComputedStyles() {
+  NS_ENSURE_TRUE(mDocShell, NS_ERROR_NOT_INITIALIZED);
+#ifdef DEBUG
+  FILE* out = stdout;
+  if (PresShell* presShell = GetPresShell(mDocShell)) {
+    presShell->ListComputedStyles(out);
+  } else {
+    fputs("null pres shell\n", out);
+  }
+#endif
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsLayoutDebuggingTools::DumpReflowStats() {
+  NS_ENSURE_TRUE(mDocShell, NS_ERROR_NOT_INITIALIZED);
+#ifdef DEBUG
+  if (RefPtr<PresShell> presShell = GetPresShell(mDocShell)) {
+#  ifdef MOZ_REFLOW_PERF
+    presShell->DumpReflows();
+#  else
+    printf("************************************************\n");
+    printf("Sorry, you have not built with MOZ_REFLOW_PERF=1\n");
+    printf("************************************************\n");
+#  endif
+  }
+#endif
+  return NS_OK;
+}
+
+nsresult nsLayoutDebuggingTools::ForceRefresh() {
+  RefPtr<nsViewManager> vm(view_manager(mDocShell));
+  if (!vm) return NS_OK;
+  nsView* root = vm->GetRootView();
+  if (root) {
+    vm->InvalidateView(root);
+  }
+  return NS_OK;
+}
+
+nsresult nsLayoutDebuggingTools::SetBoolPrefAndRefresh(const char* aPrefName,
+                                                       bool aNewVal) {
+  NS_ENSURE_TRUE(mDocShell, NS_ERROR_NOT_INITIALIZED);
+
+  nsIPrefService* prefService = Preferences::GetService();
+  NS_ENSURE_TRUE(prefService && aPrefName, NS_OK);
+
+  Preferences::SetBool(aPrefName, aNewVal);
+  prefService->SavePrefFile(nullptr);
+
+  ForceRefresh();
+
+  return NS_OK;
+}
diff --git a/layout/tools/layout-debug/src/nsLayoutDebuggingTools.h b/layout/tools/layout-debug/src/nsLayoutDebuggingTools.h
new file mode 100644
index 0000000000..f6b37fecfb
--- /dev/null
+++ b/layout/tools/layout-debug/src/nsLayoutDebuggingTools.h
@@ -0,0 +1,30 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+// vim:cindent:tabstop=4:expandtab:shiftwidth=4:
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsLayoutDebuggingTools_h
+#define nsLayoutDebuggingTools_h
+
+#include "nsILayoutDebuggingTools.h"
+#include "nsIDocShell.h"
+#include "nsCOMPtr.h"
+
+class nsLayoutDebuggingTools : public nsILayoutDebuggingTools {
+ public:
+  nsLayoutDebuggingTools();
+
+  NS_DECL_ISUPPORTS
+
+  NS_DECL_NSILAYOUTDEBUGGINGTOOLS
+
+ protected:
+  virtual ~nsLayoutDebuggingTools();
+
+  nsresult SetBoolPrefAndRefresh(const char* aPrefName, bool aNewValue);
+
+  nsCOMPtr<nsIDocShell> mDocShell;
+};
+
+#endif
diff --git a/layout/tools/layout-debug/tests/browser/browser.toml b/layout/tools/layout-debug/tests/browser/browser.toml
new file mode 100644
index 0000000000..a5fa83336e
--- /dev/null
+++ b/layout/tools/layout-debug/tests/browser/browser.toml
@@ -0,0 +1,4 @@
+[DEFAULT]
+
+["browser_openLayoutDebug.js"]
+run-if = ["debug"]
diff --git a/layout/tools/layout-debug/tests/browser/browser_openLayoutDebug.js b/layout/tools/layout-debug/tests/browser/browser_openLayoutDebug.js
new file mode 100644
index 0000000000..4402f36a7f
--- /dev/null
+++ b/layout/tools/layout-debug/tests/browser/browser_openLayoutDebug.js
@@ -0,0 +1,41 @@
+"use strict";
+
+/*
+When run locally this won't test whether the files are packaged and available
+in a distributed build unless `./mach mochitest --appname dist` is used
+(after `./mach package`)
+*/
+
+function test() {
+  waitForExplicitFinish();
+
+  const windowListener = {
+    onOpenWindow(win) {
+      info("Observed window open");
+
+      const domWindow = win.docShell.domWindow;
+      waitForFocus(() => {
+        is(
+          domWindow.location.href,
+          "chrome://layoutdebug/content/layoutdebug.xhtml",
+          "Window location is correct"
+        );
+        domWindow.close();
+      }, domWindow);
+    },
+
+    onCloseWindow() {
+      info("Observed window closed");
+      Services.wm.removeListener(this);
+      finish();
+    },
+  };
+  Services.wm.addListener(windowListener);
+
+  const menuitem = document.getElementById("menu_layout_debugger");
+  ok(menuitem, "Menuitem present");
+  if (menuitem) {
+    // open the debugger window
+    menuitem.click();
+  }
+}
diff --git a/layout/tools/layout-debug/tests/unit/test_componentsRegistered.js b/layout/tools/layout-debug/tests/unit/test_componentsRegistered.js
new file mode 100644
index 0000000000..eaf1783cb7
--- /dev/null
+++ b/layout/tools/layout-debug/tests/unit/test_componentsRegistered.js
@@ -0,0 +1,6 @@
+function run_test() {
+  Assert.ok("@mozilla.org/layout-debug/layout-debuggingtools;1" in Cc);
+  Assert.ok(
+    "@mozilla.org/commandlinehandler/general-startup;1?type=layoutdebug" in Cc
+  );
+}
diff --git a/layout/tools/layout-debug/tests/unit/xpcshell.toml b/layout/tools/layout-debug/tests/unit/xpcshell.toml
new file mode 100644
index 0000000000..f6e9021291
--- /dev/null
+++ b/layout/tools/layout-debug/tests/unit/xpcshell.toml
@@ -0,0 +1,4 @@
+[DEFAULT]
+head = ""
+
+["test_componentsRegistered.js"]
diff --git a/layout/tools/layout-debug/ui/content/layoutdebug.ftl b/layout/tools/layout-debug/ui/content/layoutdebug.ftl
new file mode 100644
index 0000000000..98c6fa3b92
--- /dev/null
+++ b/layout/tools/layout-debug/ui/content/layoutdebug.ftl
@@ -0,0 +1,81 @@
+# 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/.
+
+### This file is not in a locales directory to prevent it from being
+### translated as the layout debugger is only available in debug builds.
+
+layoutdebug-main-window =
+    .title = Layout Debugger
+
+layoutdebug-back-button =
+    .label = Back
+layoutdebug-forward-button =
+    .label = Forward
+layoutdebug-reload-button =
+    .label = Reload
+layoutdebug-stop-button =
+    .label = Stop
+
+## Toggle Menu
+
+layoutdebug-toggle-menu =
+    .label = Toggle
+    .accesskey = T
+layoutdebug-paint-dumping =
+    .label = Paint Dumping
+    .accesskey = P
+layoutdebug-invalidate-dumping =
+    .label = Invalidate Dumping
+    .accesskey = I
+layoutdebug-event-dumping =
+    .label = Event Dumping
+    .accesskey = E
+layoutdebug-motion-event-dumping =
+    .label = Motion Event Dumping
+    .accesskey = M
+layoutdebug-crossing-event-dumping =
+    .label = Crossing Event Dumping
+    .accesskey = C
+layoutdebug-reflow-counts =
+    .label = Reflow Counts
+    .accesskey = R
+layoutdebug-paged-mode =
+    .label = Paged Mode
+    .accesskey = g
+
+## Dump Menu
+
+layoutdebug-dump-menu =
+    .label = Dump
+    .accesskey = D
+layoutdebug-dump-content =
+    .label = Content
+    .accesskey = C
+layoutdebug-dump-frames =
+    .label = Frames (app units)
+    .accesskey = F
+layoutdebug-dump-frames-in-css-pixels =
+    .label = Frames (CSS pixels)
+    .accesskey = p
+layoutdebug-dump-text-runs =
+    .label = Text Runs
+    .accesskey = T
+layoutdebug-dump-views =
+    .label = Views and Widgets
+    .accesskey = V
+layoutdebug-dump-counter-manager =
+    .label = CSS Counters
+    .accesskey = n
+layoutdebug-dump-style-sheets =
+    .label = Style Sheets
+    .accesskey = S
+layoutdebug-dump-matched-rules =
+    .label = Matched CSS Rules
+    .accesskey = M
+layoutdebug-dump-computed-styles =
+    .label = Style Contexts
+    .accesskey = x
+layoutdebug-dump-reflow-stats =
+    .label = Reflow Statistics
+    .accesskey = R
diff --git a/layout/tools/layout-debug/ui/content/layoutdebug.js b/layout/tools/layout-debug/ui/content/layoutdebug.js
new file mode 100644
index 0000000000..0c68f0155c
--- /dev/null
+++ b/layout/tools/layout-debug/ui/content/layoutdebug.js
@@ -0,0 +1,520 @@
+/* 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/. */
+
+var gArgs;
+var gBrowser;
+var gURLBar;
+var gDebugger;
+var gMultiProcessBrowser = window.docShell.QueryInterface(
+  Ci.nsILoadContext
+).useRemoteTabs;
+var gFissionBrowser = window.docShell.QueryInterface(
+  Ci.nsILoadContext
+).useRemoteSubframes;
+var gWritingProfile = false;
+var gWrittenProfile = false;
+
+const { E10SUtils } = ChromeUtils.importESModule(
+  "resource://gre/modules/E10SUtils.sys.mjs"
+);
+const lazy = {};
+ChromeUtils.defineESModuleGetters(lazy, {
+  BrowserToolboxLauncher:
+    "resource://devtools/client/framework/browser-toolbox/Launcher.sys.mjs",
+});
+
+const FEATURES = {
+  paintDumping: "nglayout.debug.paint_dumping",
+  invalidateDumping: "nglayout.debug.invalidate_dumping",
+  eventDumping: "nglayout.debug.event_dumping",
+  motionEventDumping: "nglayout.debug.motion_event_dumping",
+  crossingEventDumping: "nglayout.debug.crossing_event_dumping",
+  reflowCounts: "layout.reflow.showframecounts",
+};
+
+const COMMANDS = [
+  "dumpContent",
+  "dumpFrames",
+  "dumpFramesInCSSPixels",
+  "dumpTextRuns",
+  "dumpViews",
+  "dumpCounterManager",
+  "dumpStyleSheets",
+  "dumpMatchedRules",
+  "dumpComputedStyles",
+  "dumpReflowStats",
+];
+
+class Debugger {
+  constructor() {
+    this._flags = new Map();
+    this._pagedMode = false;
+    this._attached = false;
+
+    for (let [name, pref] of Object.entries(FEATURES)) {
+      this._flags.set(name, !!Services.prefs.getBoolPref(pref, false));
+    }
+
+    this.attachBrowser();
+  }
+
+  detachBrowser() {
+    if (!this._attached) {
+      return;
+    }
+    gBrowser.removeProgressListener(this._progressListener);
+    this._progressListener = null;
+    this._attached = false;
+  }
+
+  attachBrowser() {
+    if (this._attached) {
+      throw "already attached";
+    }
+    this._progressListener = new nsLDBBrowserContentListener();
+    gBrowser.addProgressListener(this._progressListener);
+    this._attached = true;
+  }
+
+  dumpProcessIDs() {
+    let parentPid = Services.appinfo.processID;
+    let [contentPid, ...framePids] = E10SUtils.getBrowserPids(
+      gBrowser,
+      gFissionBrowser
+    );
+
+    dump(`Parent pid: ${parentPid}\n`);
+    dump(`Content pid: ${contentPid || "-"}\n`);
+    if (gFissionBrowser) {
+      dump(`Subframe pids: ${framePids.length ? framePids.join(", ") : "-"}\n`);
+    }
+  }
+
+  get pagedMode() {
+    return this._pagedMode;
+  }
+
+  set pagedMode(v) {
+    v = !!v;
+    this._pagedMode = v;
+    this.setPagedMode(this._pagedMode);
+  }
+
+  setPagedMode(v) {
+    this._sendMessage("setPagedMode", v);
+  }
+
+  openDevTools() {
+    lazy.BrowserToolboxLauncher.init();
+  }
+
+  async _sendMessage(name, arg) {
+    await this._sendMessageTo(gBrowser.browsingContext, name, arg);
+  }
+
+  async _sendMessageTo(context, name, arg) {
+    let global = context.currentWindowGlobal;
+    if (global) {
+      await global
+        .getActor("LayoutDebug")
+        .sendQuery("LayoutDebug:Call", { name, arg });
+    }
+
+    for (let c of context.children) {
+      await this._sendMessageTo(c, name, arg);
+    }
+  }
+}
+
+for (let [name, pref] of Object.entries(FEATURES)) {
+  Object.defineProperty(Debugger.prototype, name, {
+    get: function () {
+      return this._flags.get(name);
+    },
+    set: function (v) {
+      v = !!v;
+      Services.prefs.setBoolPref(pref, v);
+      this._flags.set(name, v);
+      // XXX PresShell should watch for this pref change itself.
+      if (name == "reflowCounts") {
+        this._sendMessage("setReflowCounts", v);
+      }
+      this._sendMessage("forceRefresh");
+    },
+  });
+}
+
+for (let name of COMMANDS) {
+  Debugger.prototype[name] = function () {
+    this._sendMessage(name);
+  };
+}
+
+function autoCloseIfNeeded(aCrash) {
+  if (!gArgs.autoclose) {
+    return;
+  }
+  setTimeout(function () {
+    if (aCrash) {
+      let browser = document.createXULElement("browser");
+      // FIXME(emilio): we could use gBrowser if we bothered get the process switches right.
+      //
+      // Doesn't seem worth for this particular case.
+      document.documentElement.appendChild(browser);
+      browser.loadURI(Services.io.newURI("about:crashparent"), {
+        triggeringPrincipal:
+          Services.scriptSecurityManager.getSystemPrincipal(),
+      });
+      return;
+    }
+    if (gArgs.profile && Services.profiler) {
+      dumpProfile();
+    } else {
+      Services.startup.quit(Ci.nsIAppStartup.eAttemptQuit);
+    }
+  }, gArgs.delay * 1000);
+}
+
+function nsLDBBrowserContentListener() {
+  this.init();
+}
+
+nsLDBBrowserContentListener.prototype = {
+  init: function () {
+    this.mStatusText = document.getElementById("status-text");
+    this.mForwardButton = document.getElementById("forward-button");
+    this.mBackButton = document.getElementById("back-button");
+    this.mStopButton = document.getElementById("stop-button");
+  },
+
+  QueryInterface: ChromeUtils.generateQI([
+    "nsIWebProgressListener",
+    "nsISupportsWeakReference",
+  ]),
+
+  // nsIWebProgressListener implementation
+  onStateChange: function (aWebProgress, aRequest, aStateFlags, aStatus) {
+    if (!(aStateFlags & Ci.nsIWebProgressListener.STATE_IS_NETWORK)) {
+      return;
+    }
+
+    if (aStateFlags & Ci.nsIWebProgressListener.STATE_START) {
+      this.setButtonEnabled(this.mStopButton, true);
+      this.setButtonEnabled(this.mForwardButton, gBrowser.canGoForward);
+      this.setButtonEnabled(this.mBackButton, gBrowser.canGoBack);
+      this.mStatusText.value = "loading...";
+      this.mLoading = true;
+    } else if (aStateFlags & Ci.nsIWebProgressListener.STATE_STOP) {
+      this.setButtonEnabled(this.mStopButton, false);
+      this.mStatusText.value = gURLBar.value + " loaded";
+      this.mLoading = false;
+
+      if (gDebugger.pagedMode) {
+        // Change to paged mode after the page is loaded.
+        gDebugger.setPagedMode(true);
+      }
+
+      if (gBrowser.currentURI.spec != "about:blank") {
+        // We check for about:blank just to avoid one or two STATE_STOP
+        // notifications that occur before the loadURI() call completes.
+        // This does mean that --autoclose doesn't work when the URL on
+        // the command line is about:blank (or not specified), but that's
+        // not a big deal.
+        autoCloseIfNeeded(false);
+      }
+    }
+  },
+
+  onProgressChange: function (
+    aWebProgress,
+    aRequest,
+    aCurSelfProgress,
+    aMaxSelfProgress,
+    aCurTotalProgress,
+    aMaxTotalProgress
+  ) {},
+
+  onLocationChange: function (aWebProgress, aRequest, aLocation, aFlags) {
+    gURLBar.value = aLocation.spec;
+    this.setButtonEnabled(this.mForwardButton, gBrowser.canGoForward);
+    this.setButtonEnabled(this.mBackButton, gBrowser.canGoBack);
+  },
+
+  onStatusChange: function (aWebProgress, aRequest, aStatus, aMessage) {
+    this.mStatusText.value = aMessage;
+  },
+
+  onSecurityChange: function (aWebProgress, aRequest, aState) {},
+
+  onContentBlockingEvent: function (aWebProgress, aRequest, aEvent) {},
+
+  // non-interface methods
+  setButtonEnabled: function (aButtonElement, aEnabled) {
+    if (aEnabled) {
+      aButtonElement.removeAttribute("disabled");
+    } else {
+      aButtonElement.setAttribute("disabled", "true");
+    }
+  },
+
+  mStatusText: null,
+  mForwardButton: null,
+  mBackButton: null,
+  mStopButton: null,
+
+  mLoading: false,
+};
+
+function parseArguments() {
+  let args = {
+    url: null,
+    autoclose: false,
+    delay: 0,
+    paged: false,
+  };
+  if (window.arguments) {
+    args.url = window.arguments[0];
+    for (let i = 1; i < window.arguments.length; ++i) {
+      let arg = window.arguments[i];
+      if (/^autoclose=(.*)$/.test(arg)) {
+        args.autoclose = true;
+        args.delay = +RegExp.$1;
+      } else if (/^profile=(.*)$/.test(arg)) {
+        args.profile = true;
+        args.profileFilename = RegExp.$1;
+      } else if (/^paged$/.test(arg)) {
+        args.paged = true;
+      } else {
+        throw `Unknown option ${arg}`;
+      }
+    }
+  }
+  return args;
+}
+
+const TabCrashedObserver = {
+  observe(subject, topic, data) {
+    switch (topic) {
+      case "ipc:content-shutdown":
+        subject.QueryInterface(Ci.nsIPropertyBag2);
+        if (!subject.get("abnormal")) {
+          return;
+        }
+        break;
+      case "oop-frameloader-crashed":
+        break;
+    }
+    autoCloseIfNeeded(true);
+  },
+};
+
+function OnLDBLoad() {
+  gBrowser = document.getElementById("browser");
+  gURLBar = document.getElementById("urlbar");
+
+  try {
+    ChromeUtils.registerWindowActor("LayoutDebug", {
+      child: {
+        esModuleURI: "resource://gre/actors/LayoutDebugChild.sys.mjs",
+      },
+      allFrames: true,
+    });
+  } catch (ex) {
+    // Only register the actor once.
+  }
+
+  gDebugger = new Debugger();
+
+  Services.obs.addObserver(TabCrashedObserver, "ipc:content-shutdown");
+  Services.obs.addObserver(TabCrashedObserver, "oop-frameloader-crashed");
+
+  // Pretend slightly to be like a normal browser, so that SessionStore.sys.mjs
+  // doesn't get too confused.  The effect is that we'll never switch process
+  // type when navigating, and for layout debugging purposes we don't bother
+  // about getting that right.
+  gBrowser.getTabForBrowser = function () {
+    return null;
+  };
+
+  gArgs = parseArguments();
+
+  if (gArgs.profile) {
+    if (Services.profiler) {
+      if (!Services.env.exists("MOZ_PROFILER_SYMBOLICATE")) {
+        dump(
+          "Warning: MOZ_PROFILER_SYMBOLICATE environment variable not set; " +
+            "profile will not be symbolicated.\n"
+        );
+      }
+      Services.profiler.StartProfiler(
+        1 << 20,
+        1,
+        ["default"],
+        ["GeckoMain", "Compositor", "Renderer", "RenderBackend", "StyleThread"]
+      );
+      if (gArgs.url) {
+        // Switch to the right kind of content process, and wait a bit so that
+        // the profiler has had a chance to attach to it.
+        loadStringURI(gArgs.url, { delayLoad: 3000 });
+        return;
+      }
+    } else {
+      dump("Cannot profile Layout Debugger; profiler was not compiled in.\n");
+    }
+  }
+
+  // The URI is not loaded yet. Just set the internal variable.
+  gDebugger._pagedMode = gArgs.paged;
+
+  if (gArgs.url) {
+    loadStringURI(gArgs.url);
+  }
+
+  // Some command line arguments may toggle menu items. Call this after
+  // processing all the arguments.
+  checkPersistentMenus();
+}
+
+function checkPersistentMenu(item) {
+  var menuitem = document.getElementById("menu_" + item);
+  menuitem.setAttribute("checked", gDebugger[item]);
+}
+
+function checkPersistentMenus() {
+  // Restore the toggles that are stored in prefs.
+  checkPersistentMenu("paintDumping");
+  checkPersistentMenu("invalidateDumping");
+  checkPersistentMenu("eventDumping");
+  checkPersistentMenu("motionEventDumping");
+  checkPersistentMenu("crossingEventDumping");
+  checkPersistentMenu("reflowCounts");
+  checkPersistentMenu("pagedMode");
+}
+
+function dumpProfile() {
+  gWritingProfile = true;
+
+  let cwd = Services.dirsvc.get("CurWorkD", Ci.nsIFile).path;
+  let filename = PathUtils.join(cwd, gArgs.profileFilename);
+
+  dump(`Writing profile to ${filename}...\n`);
+
+  Services.profiler.dumpProfileToFileAsync(filename).then(function () {
+    gWritingProfile = false;
+    gWrittenProfile = true;
+    dump(`done\n`);
+    Services.startup.quit(Ci.nsIAppStartup.eAttemptQuit);
+  });
+}
+
+function OnLDBBeforeUnload(event) {
+  if (gArgs.profile && Services.profiler) {
+    if (gWrittenProfile) {
+      // We've finished writing the profile.  Allow the window to close.
+      return;
+    }
+
+    event.preventDefault();
+
+    if (gWritingProfile) {
+      // Wait for the profile to finish being written out.
+      return;
+    }
+
+    // The dumpProfileToFileAsync call can block for a while, so run it off a
+    // timeout to avoid annoying the window manager if we're doing this in
+    // response to clicking the window's close button.
+    setTimeout(dumpProfile, 0);
+  }
+}
+
+function OnLDBUnload() {
+  gDebugger.detachBrowser();
+  Services.obs.removeObserver(TabCrashedObserver, "ipc:content-shutdown");
+  Services.obs.removeObserver(TabCrashedObserver, "oop-frameloader-crashed");
+}
+
+function toggle(menuitem) {
+  // trim the initial "menu_"
+  var feature = menuitem.id.substring(5);
+  gDebugger[feature] = menuitem.getAttribute("checked") == "true";
+}
+
+function openFile() {
+  var fp = Cc["@mozilla.org/filepicker;1"].createInstance(Ci.nsIFilePicker);
+  fp.init(window, "Select a File", Ci.nsIFilePicker.modeOpen);
+  fp.appendFilters(Ci.nsIFilePicker.filterHTML | Ci.nsIFilePicker.filterAll);
+  fp.open(rv => {
+    if (
+      rv == Ci.nsIFilePicker.returnOK &&
+      fp.fileURL.spec &&
+      fp.fileURL.spec.length > 0
+    ) {
+      loadURIObject(fp.fileURL);
+    }
+  });
+}
+
+// A simplified version of the function with the same name in tabbrowser.js.
+function updateBrowserRemotenessByURL(aURL) {
+  let oa = E10SUtils.predictOriginAttributes({ browser: gBrowser });
+  let remoteType = E10SUtils.getRemoteTypeForURIObject(aURL, {
+    multiProcess: gMultiProcessBrowser,
+    remoteSubFrames: gFissionBrowser,
+    preferredRemoteType: gBrowser.remoteType,
+    currentURI: gBrowser.currentURI,
+    originAttributes: oa,
+  });
+  if (gBrowser.remoteType != remoteType) {
+    gDebugger.detachBrowser();
+    if (remoteType == E10SUtils.NOT_REMOTE) {
+      gBrowser.removeAttribute("remote");
+      gBrowser.removeAttribute("remoteType");
+    } else {
+      gBrowser.setAttribute("remote", "true");
+      gBrowser.setAttribute("remoteType", remoteType);
+    }
+    gBrowser.changeRemoteness({ remoteType });
+    gBrowser.construct();
+    gDebugger.attachBrowser();
+  }
+}
+
+function loadStringURI(aURLString, aOptions) {
+  let realURL;
+  try {
+    realURL = Services.uriFixup.getFixupURIInfo(aURLString).preferredURI;
+  } catch (ex) {
+    alert(
+      "Couldn't work out how to create a URL from input: " +
+        aURLString.substring(0, 100)
+    );
+    return;
+  }
+  return loadURIObject(realURL, aOptions);
+}
+
+async function loadURIObject(aURL, { delayLoad } = {}) {
+  // We don't bother trying to handle navigations within the browser to new URLs
+  // that should be loaded in a different process.
+  updateBrowserRemotenessByURL(aURL);
+  // When attaching the profiler we may want to delay the actual load a bit
+  // after switching remoteness.
+  if (delayLoad) {
+    await new Promise(r => setTimeout(r, delayLoad));
+  }
+  gBrowser.loadURI(aURL, {
+    triggeringPrincipal: Services.scriptSecurityManager.getSystemPrincipal(),
+  });
+}
+
+function focusURLBar() {
+  gURLBar.focus();
+  gURLBar.select();
+}
+
+function go() {
+  loadStringURI(gURLBar.value);
+  gBrowser.focus();
+}
diff --git a/layout/tools/layout-debug/ui/content/layoutdebug.xhtml b/layout/tools/layout-debug/ui/content/layoutdebug.xhtml
new file mode 100644
index 0000000000..995a1a4b44
--- /dev/null
+++ b/layout/tools/layout-debug/ui/content/layoutdebug.xhtml
@@ -0,0 +1,280 @@
+<?xml version="1.0"?>
+<!-- vim: set shiftwidth=2 tabstop=8 expandtab :
+   -
+   -
+   - 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/. -->
+
+<!DOCTYPE window>
+
+<!--
+
+  NOTE:  Because this window is used for layout regression tests, the
+  persist attribute should never be used on anything.  Otherwise there
+  is a risk of running baseline and verify runs under different
+  conditions.
+
+-->
+
+<window
+  xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+  xmlns:html="http://www.w3.org/1999/xhtml"
+  id="main-window"
+  align="stretch"
+  data-l10n-id="layoutdebug-main-window"
+  windowtype="mozapp:layoutdebug"
+  onload="OnLDBLoad();"
+  onclose="OnLDBBeforeUnload(event);"
+  onunload="OnLDBUnload();"
+  width="1024"
+  height="768"
+  screenX="4"
+  screenY="4"
+>
+  <linkset>
+    <html:link rel="stylesheet" href="chrome://global/skin/global.css" />
+
+    <html:link rel="localization" href="layoutdebug/layoutdebug.ftl" />
+  </linkset>
+
+  <script src="chrome://layoutdebug/content/layoutdebug.js" />
+
+  <commandset id="tasksCommands">
+    <command id="cmd_open" oncommand="openFile();" />
+    <command id="cmd_close" oncommand="window.close();" />
+    <command id="cmd_focusURLBar" oncommand="focusURLBar();" />
+    <command id="cmd_reload" oncommand="gBrowser.reload();" />
+    <command id="cmd_dumpContent" oncommand="gDebugger.dumpContent();" />
+    <command id="cmd_dumpFrames" oncommand="gDebugger.dumpFrames();" />
+    <command
+      id="cmd_dumpFramesInCSSPixels"
+      oncommand="gDebugger.dumpFramesInCSSPixels();"
+    />
+    <command id="cmd_dumpTextRuns" oncommand="gDebugger.dumpTextRuns();" />
+    <command id="cmd_openDevTools" oncommand="gDebugger.openDevTools();" />
+  </commandset>
+
+  <keyset id="tasksKeys">
+    <key id="key_open" key="O" modifiers="accel" command="cmd_open" />
+    <key id="key_close" key="W" modifiers="accel" command="cmd_close" />
+    <key
+      id="key_focusURLBar"
+      key="L"
+      modifiers="accel"
+      command="cmd_focusURLBar"
+    />
+    <key id="key_reload" key="R" modifiers="accel" command="cmd_reload" />
+    <key
+      id="key_dumpContent"
+      key="D"
+      modifiers="accel"
+      command="cmd_dumpContent"
+    />
+    <!-- "D" means DOM tree -->
+    <key
+      id="key_dumpFrames"
+      key="F"
+      modifiers="accel"
+      command="cmd_dumpFrames"
+    />
+    <key
+      id="key_dumpFramesInCSSPixels"
+      key="P"
+      modifiers="accel"
+      command="cmd_dumpFramesInCSSPixels"
+    />
+    <key
+      id="key_dumpTextRuns"
+      key="T"
+      modifiers="accel"
+      command="cmd_dumpTextRuns"
+    />
+    <key id="key_devTools" keycode="VK_F12" command="cmd_openDevTools" />
+  </keyset>
+
+  <vbox flex="1">
+    <toolbox>
+      <toolbar type="menubar">
+        <menubar id="main-menubar">
+          <menu id="menu_file" label="File" accesskey="F">
+            <menupopup id="menu_FilePopup">
+              <menuitem
+                id="menu_open"
+                label="Open File…"
+                accesskey="O"
+                key="key_open"
+                command="cmd_open"
+              />
+              <menuitem
+                id="menu_close"
+                label="Close"
+                accesskey="C"
+                key="key_close"
+                command="cmd_close"
+              />
+            </menupopup>
+          </menu>
+          <menu data-l10n-id="layoutdebug-toggle-menu">
+            <menupopup>
+              <menuitem
+                type="checkbox"
+                id="menu_paintDumping"
+                data-l10n-id="layoutdebug-paint-dumping"
+                oncommand="toggle(this);"
+              />
+              <menuitem
+                type="checkbox"
+                id="menu_invalidateDumping"
+                data-l10n-id="layoutdebug-invalidate-dumping"
+                oncommand="toggle(this);"
+              />
+              <menuseparator />
+              <menuitem
+                type="checkbox"
+                id="menu_eventDumping"
+                data-l10n-id="layoutdebug-event-dumping"
+                oncommand="toggle(this);"
+              />
+              <menuitem
+                type="checkbox"
+                id="menu_motionEventDumping"
+                data-l10n-id="layoutdebug-motion-event-dumping"
+                oncommand="toggle(this);"
+              />
+              <menuitem
+                type="checkbox"
+                id="menu_crossingEventDumping"
+                data-l10n-id="layoutdebug-crossing-event-dumping"
+                oncommand="toggle(this);"
+              />
+              <menuseparator />
+              <menuitem
+                type="checkbox"
+                id="menu_reflowCounts"
+                data-l10n-id="layoutdebug-reflow-counts"
+                oncommand="toggle(this);"
+              />
+              <menuitem
+                type="checkbox"
+                id="menu_pagedMode"
+                data-l10n-id="layoutdebug-paged-mode"
+                oncommand="toggle(this);"
+              />
+            </menupopup>
+          </menu>
+          <menu data-l10n-id="layoutdebug-dump-menu">
+            <menupopup>
+              <menuitem
+                id="menu_processIDs"
+                label="Process IDs"
+                accesskey="P"
+                oncommand="gDebugger.dumpProcessIDs();"
+              />
+              <menuitem
+                id="menu_dumpContent"
+                data-l10n-id="layoutdebug-dump-content"
+                oncommand="gDebugger.dumpContent();"
+              />
+              <menuitem
+                id="menu_dumpFrames"
+                data-l10n-id="layoutdebug-dump-frames"
+                oncommand="gDebugger.dumpFrames();"
+              />
+              <menuitem
+                id="menu_dumpFramesInCSSPixels"
+                data-l10n-id="layoutdebug-dump-frames-in-css-pixels"
+                oncommand="gDebugger.dumpFramesInCSSPixels();"
+              />
+              <menuitem
+                id="menu_dumpTextRuns"
+                data-l10n-id="layoutdebug-dump-text-runs"
+                oncommand="gDebugger.dumpTextRuns();"
+              />
+              <menuitem
+                id="menu_dumpViews"
+                data-l10n-id="layoutdebug-dump-views"
+                oncommand="gDebugger.dumpViews();"
+              />
+              <menuitem
+                id="menu_dumpCounterManager"
+                data-l10n-id="layoutdebug-dump-counter-manager"
+                oncommand="gDebugger.dumpCounterManager();"
+              />
+              <menuseparator />
+              <menuitem
+                id="menu_dumpStyleSheets"
+                data-l10n-id="layoutdebug-dump-style-sheets"
+                oncommand="gDebugger.dumpStyleSheets();"
+              />
+              <menuitem
+                id="menu_dumpMatchedRules"
+                data-l10n-id="layoutdebug-dump-matched-rules"
+                oncommand="gDebugger.dumpMatchedRules();"
+              />
+              <menuitem
+                id="menu_dumpComputedStyles"
+                data-l10n-id="layoutdebug-dump-computed-styles"
+                oncommand="gDebugger.dumpComputedStyles();"
+              />
+              <menuseparator />
+              <menuitem
+                id="menu_dumpReflowStats"
+                data-l10n-id="layoutdebug-dump-reflow-stats"
+                oncommand="gDebugger.dumpReflowStats();"
+              />
+            </menupopup>
+          </menu>
+          <menu id="tasksMenu" />
+          <menu id="menu_Help" />
+        </menubar>
+      </toolbar>
+
+      <toolbar>
+        <toolbarbutton
+          id="back-button"
+          class="toolbarbutton-1"
+          data-l10n-id="layoutdebug-back-button"
+          oncommand="gBrowser.goBack();"
+        />
+        <toolbarbutton
+          id="forward-button"
+          class="toolbarbutton-1"
+          data-l10n-id="layoutdebug-forward-button"
+          oncommand="gBrowser.goForward();"
+        />
+        <toolbarbutton
+          id="reload-button"
+          class="toolbarbutton-1"
+          data-l10n-id="layoutdebug-reload-button"
+          command="cmd_reload"
+        />
+        <toolbarbutton
+          id="stop-button"
+          class="toolbarbutton-1"
+          data-l10n-id="layoutdebug-stop-button"
+          oncommand="gBrowser.stop();"
+        />
+
+        <html:input
+          id="urlbar"
+          style="flex: 1"
+          onkeypress="if (event.keyCode == 13) go();"
+        />
+      </toolbar>
+    </toolbox>
+
+    <browser
+      flex="1"
+      id="browser"
+      type="content"
+      primary="true"
+      remote="true"
+      remoteType="web"
+    />
+
+    <hbox>
+      <description id="status-text" value="" />
+    </hbox>
+  </vbox>
+</window>
diff --git a/layout/tools/layout-debug/ui/jar.mn b/layout/tools/layout-debug/ui/jar.mn
new file mode 100644
index 0000000000..01d6b08012
--- /dev/null
+++ b/layout/tools/layout-debug/ui/jar.mn
@@ -0,0 +1,8 @@
+# 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/.
+
+layoutdebug.jar:
+% content layoutdebug %content/layoutdebug/
+  content/layoutdebug/layoutdebug.xhtml              (content/layoutdebug.xhtml)
+  content/layoutdebug/layoutdebug.js               (content/layoutdebug.js)
diff --git a/layout/tools/layout-debug/ui/moz.build b/layout/tools/layout-debug/ui/moz.build
new file mode 100644
index 0000000000..d988c0ff9b
--- /dev/null
+++ b/layout/tools/layout-debug/ui/moz.build
@@ -0,0 +1,7 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+JAR_MANIFESTS += ["jar.mn"]