Adding upstream version 86.0.1.upstream/86.0.1upstream

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

28 files changed, 2502 insertions, 0 deletions

diff --git a/widget/headless/HeadlessClipboard.cpp b/widget/headless/HeadlessClipboard.cpp
new file mode 100644
index 0000000000..0d8c7fe572
--- /dev/null
+++ b/widget/headless/HeadlessClipboard.cpp
@@ -0,0 +1,112 @@
+/* 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 "HeadlessClipboard.h"
+
+#include "nsISupportsPrimitives.h"
+#include "nsComponentManagerUtils.h"
+#include "nsCOMPtr.h"
+
+namespace mozilla {
+namespace widget {
+
+NS_IMPL_ISUPPORTS(HeadlessClipboard, nsIClipboard)
+
+HeadlessClipboard::HeadlessClipboard()
+    : mClipboard(MakeUnique<HeadlessClipboardData>()) {}
+
+NS_IMETHODIMP
+HeadlessClipboard::SetData(nsITransferable* aTransferable,
+                           nsIClipboardOwner* anOwner,
+                           int32_t aWhichClipboard) {
+  if (aWhichClipboard != kGlobalClipboard) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  // Clear out the clipboard in order to set the new data.
+  EmptyClipboard(aWhichClipboard);
+
+  // Only support plain text for now.
+  nsCOMPtr<nsISupports> clip;
+  nsresult rv =
+      aTransferable->GetTransferData(kUnicodeMime, getter_AddRefs(clip));
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  nsCOMPtr<nsISupportsString> wideString = do_QueryInterface(clip);
+  if (!wideString) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  nsAutoString utf16string;
+  wideString->GetData(utf16string);
+  mClipboard->SetText(utf16string);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+HeadlessClipboard::GetData(nsITransferable* aTransferable,
+                           int32_t aWhichClipboard) {
+  if (aWhichClipboard != kGlobalClipboard) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+
+  nsresult rv;
+  nsCOMPtr<nsISupportsString> dataWrapper =
+      do_CreateInstance(NS_SUPPORTS_STRING_CONTRACTID, &rv);
+  rv = dataWrapper->SetData(mClipboard->GetText());
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  nsCOMPtr<nsISupports> genericDataWrapper = do_QueryInterface(dataWrapper);
+  rv = aTransferable->SetTransferData(kUnicodeMime, genericDataWrapper);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+HeadlessClipboard::EmptyClipboard(int32_t aWhichClipboard) {
+  if (aWhichClipboard != kGlobalClipboard) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  mClipboard->Clear();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+HeadlessClipboard::HasDataMatchingFlavors(
+    const nsTArray<nsCString>& aFlavorList, int32_t aWhichClipboard,
+    bool* aHasType) {
+  *aHasType = false;
+  if (aWhichClipboard != kGlobalClipboard) {
+    return NS_ERROR_NOT_IMPLEMENTED;
+  }
+  // Retrieve the union of all aHasType in aFlavorList
+  for (auto& flavor : aFlavorList) {
+    if (flavor.EqualsLiteral(kUnicodeMime) && mClipboard->HasText()) {
+      *aHasType = true;
+      break;
+    }
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+HeadlessClipboard::SupportsSelectionClipboard(bool* aIsSupported) {
+  *aIsSupported = false;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+HeadlessClipboard::SupportsFindClipboard(bool* _retval) {
+  NS_ENSURE_ARG_POINTER(_retval);
+
+  *_retval = false;
+  return NS_OK;
+}
+
+}  // namespace widget
+}  // namespace mozilla
diff --git a/widget/headless/HeadlessClipboard.h b/widget/headless/HeadlessClipboard.h
new file mode 100644
index 0000000000..da7819e195
--- /dev/null
+++ b/widget/headless/HeadlessClipboard.h
@@ -0,0 +1,33 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_widget_HeadlessClipboard_h
+#define mozilla_widget_HeadlessClipboard_h
+
+#include "nsIClipboard.h"
+#include "mozilla/UniquePtr.h"
+#include "HeadlessClipboardData.h"
+
+namespace mozilla {
+namespace widget {
+
+class HeadlessClipboard final : public nsIClipboard {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSICLIPBOARD
+
+  HeadlessClipboard();
+
+ protected:
+  ~HeadlessClipboard() = default;
+
+ private:
+  UniquePtr<HeadlessClipboardData> mClipboard;
+};
+
+}  // namespace widget
+}  // namespace mozilla
+
+#endif
diff --git a/widget/headless/HeadlessClipboardData.cpp b/widget/headless/HeadlessClipboardData.cpp
new file mode 100644
index 0000000000..3722605854
--- /dev/null
+++ b/widget/headless/HeadlessClipboardData.cpp
@@ -0,0 +1,19 @@
+/* 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 "HeadlessClipboardData.h"
+
+namespace mozilla {
+namespace widget {
+
+void HeadlessClipboardData::SetText(const nsAString& aText) { mPlain = aText; }
+
+bool HeadlessClipboardData::HasText() const { return !mPlain.IsEmpty(); }
+
+const nsAString& HeadlessClipboardData::GetText() const { return mPlain; }
+
+void HeadlessClipboardData::Clear() { mPlain.Truncate(0); }
+
+}  // namespace widget
+}  // namespace mozilla
diff --git a/widget/headless/HeadlessClipboardData.h b/widget/headless/HeadlessClipboardData.h
new file mode 100644
index 0000000000..14cb84820a
--- /dev/null
+++ b/widget/headless/HeadlessClipboardData.h
@@ -0,0 +1,34 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_widget_HeadlessClipboardData_h
+#define mozilla_widget_HeadlessClipboardData_h
+
+#include "mozilla/RefPtr.h"
+#include "nsString.h"
+
+namespace mozilla {
+namespace widget {
+
+class HeadlessClipboardData final {
+ public:
+  explicit HeadlessClipboardData() = default;
+  ~HeadlessClipboardData() = default;
+
+  // For text/plain
+  void SetText(const nsAString& aText);
+  bool HasText() const;
+  const nsAString& GetText() const;
+
+  // For other APIs
+  void Clear();
+
+ private:
+  nsAutoString mPlain;
+};
+
+}  // namespace widget
+}  // namespace mozilla
+
+#endif  // mozilla_widget_HeadlessClipboardData_h
diff --git a/widget/headless/HeadlessCompositorWidget.cpp b/widget/headless/HeadlessCompositorWidget.cpp
new file mode 100644
index 0000000000..b31a969b7a
--- /dev/null
+++ b/widget/headless/HeadlessCompositorWidget.cpp
@@ -0,0 +1,43 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/widget/PlatformWidgetTypes.h"
+#include "HeadlessCompositorWidget.h"
+#include "VsyncDispatcher.h"
+
+namespace mozilla {
+namespace widget {
+
+HeadlessCompositorWidget::HeadlessCompositorWidget(
+    const HeadlessCompositorWidgetInitData& aInitData,
+    const layers::CompositorOptions& aOptions, HeadlessWidget* aWindow)
+    : CompositorWidget(aOptions), mWidget(aWindow) {
+  mClientSize = aInitData.InitialClientSize();
+}
+
+void HeadlessCompositorWidget::ObserveVsync(VsyncObserver* aObserver) {
+  if (RefPtr<CompositorVsyncDispatcher> cvd =
+          mWidget->GetCompositorVsyncDispatcher()) {
+    cvd->SetCompositorVsyncObserver(aObserver);
+  }
+}
+
+nsIWidget* HeadlessCompositorWidget::RealWidget() { return mWidget; }
+
+void HeadlessCompositorWidget::NotifyClientSizeChanged(
+    const LayoutDeviceIntSize& aClientSize) {
+  mClientSize = aClientSize;
+}
+
+LayoutDeviceIntSize HeadlessCompositorWidget::GetClientSize() {
+  return mClientSize;
+}
+
+uintptr_t HeadlessCompositorWidget::GetWidgetKey() {
+  return reinterpret_cast<uintptr_t>(mWidget);
+}
+
+}  // namespace widget
+}  // namespace mozilla
diff --git a/widget/headless/HeadlessCompositorWidget.h b/widget/headless/HeadlessCompositorWidget.h
new file mode 100644
index 0000000000..7f91de9e67
--- /dev/null
+++ b/widget/headless/HeadlessCompositorWidget.h
@@ -0,0 +1,53 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef widget_headless_HeadlessCompositorWidget_h
+#define widget_headless_HeadlessCompositorWidget_h
+
+#include "mozilla/widget/CompositorWidget.h"
+
+#include "HeadlessWidget.h"
+
+namespace mozilla {
+namespace widget {
+
+class HeadlessCompositorWidgetInitData;
+
+class HeadlessCompositorWidget final : public CompositorWidget,
+                                       public CompositorWidgetDelegate {
+ public:
+  HeadlessCompositorWidget(const HeadlessCompositorWidgetInitData& aInitData,
+                           const layers::CompositorOptions& aOptions,
+                           HeadlessWidget* aWindow);
+
+  void NotifyClientSizeChanged(const LayoutDeviceIntSize& aClientSize);
+
+  // CompositorWidget Overrides
+
+  uintptr_t GetWidgetKey() override;
+
+  LayoutDeviceIntSize GetClientSize() override;
+
+  nsIWidget* RealWidget() override;
+  CompositorWidgetDelegate* AsDelegate() override { return this; }
+
+  void ObserveVsync(VsyncObserver* aObserver) override;
+
+  // CompositorWidgetDelegate Overrides
+
+  HeadlessCompositorWidget* AsHeadlessCompositorWidget() override {
+    return this;
+  }
+
+ private:
+  HeadlessWidget* mWidget;
+
+  LayoutDeviceIntSize mClientSize;
+};
+
+}  // namespace widget
+}  // namespace mozilla
+
+#endif  // widget_headless_HeadlessCompositor_h
diff --git a/widget/headless/HeadlessKeyBindings.cpp b/widget/headless/HeadlessKeyBindings.cpp
new file mode 100644
index 0000000000..1704612426
--- /dev/null
+++ b/widget/headless/HeadlessKeyBindings.cpp
@@ -0,0 +1,34 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "HeadlessKeyBindings.h"
+#include "mozilla/ClearOnShutdown.h"
+
+namespace mozilla {
+namespace widget {
+
+HeadlessKeyBindings& HeadlessKeyBindings::GetInstance() {
+  static UniquePtr<HeadlessKeyBindings> sInstance;
+  if (!sInstance) {
+    sInstance.reset(new HeadlessKeyBindings());
+    ClearOnShutdown(&sInstance);
+  }
+  return *sInstance;
+}
+
+nsresult HeadlessKeyBindings::AttachNativeKeyEvent(
+    WidgetKeyboardEvent& aEvent) {
+  // Stub for non-mac platforms.
+  return NS_OK;
+}
+
+void HeadlessKeyBindings::GetEditCommands(
+    nsIWidget::NativeKeyBindingsType aType, const WidgetKeyboardEvent& aEvent,
+    nsTArray<CommandInt>& aCommands) {
+  // Stub for non-mac platforms.
+}
+
+}  // namespace widget
+}  // namespace mozilla
diff --git a/widget/headless/HeadlessKeyBindings.h b/widget/headless/HeadlessKeyBindings.h
new file mode 100644
index 0000000000..c658360cf8
--- /dev/null
+++ b/widget/headless/HeadlessKeyBindings.h
@@ -0,0 +1,35 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_widget_HeadlessKeyBindings_h
+#define mozilla_widget_HeadlessKeyBindings_h
+
+#include "mozilla/TextEvents.h"
+#include "nsIWidget.h"
+#include "nsTArray.h"
+
+namespace mozilla {
+namespace widget {
+
+/**
+ * Helper to emulate native key bindings. Currently only MacOS is supported.
+ */
+
+class HeadlessKeyBindings final {
+ public:
+  HeadlessKeyBindings() = default;
+
+  static HeadlessKeyBindings& GetInstance();
+
+  void GetEditCommands(nsIWidget::NativeKeyBindingsType aType,
+                       const WidgetKeyboardEvent& aEvent,
+                       nsTArray<CommandInt>& aCommands);
+  [[nodiscard]] nsresult AttachNativeKeyEvent(WidgetKeyboardEvent& aEvent);
+};
+
+}  // namespace widget
+}  // namespace mozilla
+
+#endif  // mozilla_widget_HeadlessKeyBindings_h
diff --git a/widget/headless/HeadlessKeyBindingsCocoa.mm b/widget/headless/HeadlessKeyBindingsCocoa.mm
new file mode 100644
index 0000000000..356eec0e56
--- /dev/null
+++ b/widget/headless/HeadlessKeyBindingsCocoa.mm
@@ -0,0 +1,47 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "HeadlessKeyBindings.h"
+#import <Cocoa/Cocoa.h>
+#include "nsCocoaUtils.h"
+#include "NativeKeyBindings.h"
+#include "mozilla/ClearOnShutdown.h"
+
+namespace mozilla {
+namespace widget {
+
+HeadlessKeyBindings& HeadlessKeyBindings::GetInstance() {
+  static UniquePtr<HeadlessKeyBindings> sInstance;
+  if (!sInstance) {
+    sInstance.reset(new HeadlessKeyBindings());
+    ClearOnShutdown(&sInstance);
+  }
+  return *sInstance;
+}
+
+nsresult HeadlessKeyBindings::AttachNativeKeyEvent(WidgetKeyboardEvent& aEvent) {
+  NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NSRESULT;
+
+  aEvent.mNativeKeyEvent = nsCocoaUtils::MakeNewCococaEventFromWidgetEvent(aEvent, 0, nil);
+
+  return NS_OK;
+
+  NS_OBJC_END_TRY_ABORT_BLOCK_NSRESULT;
+}
+
+void HeadlessKeyBindings::GetEditCommands(nsIWidget::NativeKeyBindingsType aType,
+                                          const WidgetKeyboardEvent& aEvent,
+                                          nsTArray<CommandInt>& aCommands) {
+  // Convert the widget keyboard into a cocoa event so it can be translated
+  // into commands in the NativeKeyBindings.
+  WidgetKeyboardEvent modifiedEvent(aEvent);
+  modifiedEvent.mNativeKeyEvent = nsCocoaUtils::MakeNewCococaEventFromWidgetEvent(aEvent, 0, nil);
+
+  NativeKeyBindings* keyBindings = NativeKeyBindings::GetInstance(aType);
+  keyBindings->GetEditCommands(modifiedEvent, aCommands);
+}
+
+}  // namespace widget
+}  // namespace mozilla
diff --git a/widget/headless/HeadlessLookAndFeel.h b/widget/headless/HeadlessLookAndFeel.h
new file mode 100644
index 0000000000..8b6cf033fd
--- /dev/null
+++ b/widget/headless/HeadlessLookAndFeel.h
@@ -0,0 +1,65 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_widget_HeadlessLookAndFeel_h
+#define mozilla_widget_HeadlessLookAndFeel_h
+
+#include "nsXPLookAndFeel.h"
+#include "nsLookAndFeel.h"
+
+namespace mozilla {
+namespace widget {
+
+#if defined(MOZ_WIDGET_GTK)
+
+// Our nsLookAndFeel for Gtk relies on APIs that aren't available in headless
+// mode, so for processes that are unable to connect to a display server, we use
+// an implementation with hardcoded values.
+//
+// HeadlessLookAndFeel is used:
+//
+//   * in the parent process, when full headless mode (MOZ_HEADLESS=1) is
+//     enabled
+//   * in content processes, when full headless mode or headless content
+//     mode (security.sandbox.content.headless) is enabled, unless
+//     widget.remote-look-and-feel is also enabled, in which case
+//     RemoteLookAndFeel is used instead.
+//
+// The result of this is that when headless content mode is enabled, content
+// processes use values derived from the parent's nsLookAndFeel (i.e., values
+// derived from Gtk APIs) while still refraining from making any display server
+// connections.
+
+class HeadlessLookAndFeel : public nsXPLookAndFeel {
+ public:
+  explicit HeadlessLookAndFeel(const LookAndFeelCache* aCache);
+  virtual ~HeadlessLookAndFeel();
+
+  void NativeInit() final{};
+  virtual nsresult NativeGetInt(IntID aID, int32_t& aResult) override;
+  virtual nsresult NativeGetFloat(FloatID aID, float& aResult) override;
+  virtual nsresult NativeGetColor(ColorID aID, nscolor& aResult) override;
+  virtual bool NativeGetFont(FontID aID, nsString& aFontName,
+                             gfxFontStyle& aFontStyle) override;
+
+  virtual void RefreshImpl() override;
+  virtual char16_t GetPasswordCharacterImpl() override;
+  virtual bool GetEchoPasswordImpl() override;
+};
+
+#else
+
+// When possible, we simply reuse the platform's existing nsLookAndFeel
+// implementation in headless mode.
+
+typedef nsLookAndFeel HeadlessLookAndFeel;
+
+#endif
+
+}  // namespace widget
+}  // namespace mozilla
+
+#endif
diff --git a/widget/headless/HeadlessLookAndFeelGTK.cpp b/widget/headless/HeadlessLookAndFeelGTK.cpp
new file mode 100644
index 0000000000..3d4a135ee1
--- /dev/null
+++ b/widget/headless/HeadlessLookAndFeelGTK.cpp
@@ -0,0 +1,359 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "HeadlessLookAndFeel.h"
+#include "mozilla/FontPropertyTypes.h"
+#include "nsIContent.h"
+
+using mozilla::LookAndFeel;
+
+namespace mozilla {
+namespace widget {
+
+static const char16_t UNICODE_BULLET = 0x2022;
+
+HeadlessLookAndFeel::HeadlessLookAndFeel(const LookAndFeelCache* aCache) {}
+
+HeadlessLookAndFeel::~HeadlessLookAndFeel() = default;
+
+nsresult HeadlessLookAndFeel::NativeGetColor(ColorID aID, nscolor& aColor) {
+  // For headless mode, we use GetStandinForNativeColor for everything we can,
+  // and hardcoded values for everything else.
+
+  nsresult res = NS_OK;
+
+  switch (aID) {
+    // Override the solid black that GetStandinForNativeColor provides for
+    // FieldText, to match our behavior under the real GTK.
+    case ColorID::Fieldtext:
+      aColor = NS_RGB(0x21, 0x21, 0x21);
+      break;
+
+    // The rest are not provided by GetStandinForNativeColor.
+    case ColorID::IMESelectedRawTextBackground:
+    case ColorID::IMESelectedConvertedTextBackground:
+    case ColorID::IMERawInputBackground:
+    case ColorID::IMEConvertedTextBackground:
+      aColor = NS_TRANSPARENT;
+      break;
+    case ColorID::IMESelectedRawTextForeground:
+    case ColorID::IMESelectedConvertedTextForeground:
+    case ColorID::IMERawInputForeground:
+    case ColorID::IMEConvertedTextForeground:
+      aColor = NS_SAME_AS_FOREGROUND_COLOR;
+      break;
+    case ColorID::IMERawInputUnderline:
+    case ColorID::IMEConvertedTextUnderline:
+      aColor = NS_40PERCENT_FOREGROUND_COLOR;
+      break;
+    case ColorID::IMESelectedRawTextUnderline:
+    case ColorID::IMESelectedConvertedTextUnderline:
+      aColor = NS_SAME_AS_FOREGROUND_COLOR;
+      break;
+    case ColorID::MozEventreerow:
+      aColor = NS_RGB(0xff, 0xff, 0xff);
+      break;
+    case ColorID::MozGtkInfoBarText:
+      aColor = NS_RGB(0x00, 0x00, 0x00);
+      break;
+    case ColorID::MozMacButtonactivetext:
+    case ColorID::MozMacDefaultbuttontext:
+      aColor = NS_RGB(0xff, 0xff, 0xff);
+      break;
+    case ColorID::SpellCheckerUnderline:
+      aColor = NS_RGB(0xff, 0x00, 0x00);
+      break;
+    case ColorID::TextBackground:
+      aColor = NS_RGB(0xff, 0xff, 0xff);
+      break;
+    case ColorID::TextForeground:
+      aColor = NS_RGB(0x00, 0x00, 0x00);
+      break;
+    case ColorID::TextHighlightBackground:
+      aColor = NS_RGB(0xef, 0x0f, 0xff);
+      break;
+    case ColorID::TextHighlightForeground:
+      aColor = NS_RGB(0xff, 0xff, 0xff);
+      break;
+    case ColorID::TextSelectBackground:
+      aColor = NS_RGB(0xaa, 0xaa, 0xaa);
+      break;
+    case ColorID::TextSelectBackgroundAttention:
+      aColor = NS_TRANSPARENT;
+      break;
+    case ColorID::TextSelectBackgroundDisabled:
+      aColor = NS_RGB(0xaa, 0xaa, 0xaa);
+      break;
+    case ColorID::TextSelectForeground:
+      GetColor(ColorID::TextSelectBackground, aColor);
+      if (aColor == 0x000000)
+        aColor = NS_RGB(0xff, 0xff, 0xff);
+      else
+        aColor = NS_DONT_CHANGE_COLOR;
+      break;
+    case ColorID::Widget3DHighlight:
+      aColor = NS_RGB(0xa0, 0xa0, 0xa0);
+      break;
+    case ColorID::Widget3DShadow:
+      aColor = NS_RGB(0x40, 0x40, 0x40);
+      break;
+    case ColorID::WidgetBackground:
+      aColor = NS_RGB(0xdd, 0xdd, 0xdd);
+      break;
+    case ColorID::WidgetForeground:
+      aColor = NS_RGB(0x00, 0x00, 0x00);
+      break;
+    case ColorID::WidgetSelectBackground:
+      aColor = NS_RGB(0x80, 0x80, 0x80);
+      break;
+    case ColorID::WidgetSelectForeground:
+      aColor = NS_RGB(0x00, 0x00, 0x80);
+      break;
+    case ColorID::WindowBackground:
+      aColor = NS_RGB(0xff, 0xff, 0xff);
+      break;
+    case ColorID::WindowForeground:
+      aColor = NS_RGB(0x00, 0x00, 0x00);
+      break;
+    default:
+      aColor = GetStandinForNativeColor(aID);
+      break;
+  }
+
+  return res;
+}
+
+nsresult HeadlessLookAndFeel::NativeGetInt(IntID aID, int32_t& aResult) {
+  nsresult res = NS_OK;
+  // These values should be sane defaults for headless mode under GTK.
+  switch (aID) {
+    case IntID::CaretBlinkTime:
+      aResult = 567;
+      break;
+    case IntID::CaretWidth:
+      aResult = 1;
+      break;
+    case IntID::ShowCaretDuringSelection:
+      aResult = 0;
+      break;
+    case IntID::SelectTextfieldsOnKeyFocus:
+      aResult = 1;
+      break;
+    case IntID::SubmenuDelay:
+      aResult = 200;
+      break;
+    case IntID::MenusCanOverlapOSBar:
+      aResult = 0;
+      break;
+    case IntID::UseOverlayScrollbars:
+      aResult = 0;
+      break;
+    case IntID::AllowOverlayScrollbarsOverlap:
+      aResult = 0;
+      break;
+    case IntID::ShowHideScrollbars:
+      aResult = 0;
+      break;
+    case IntID::SkipNavigatingDisabledMenuItem:
+      aResult = 1;
+      break;
+    case IntID::DragThresholdX:
+    case IntID::DragThresholdY:
+      aResult = 4;
+      break;
+    case IntID::UseAccessibilityTheme:
+      aResult = 0;
+      break;
+    case IntID::ScrollArrowStyle:
+      aResult = eScrollArrow_None;
+      break;
+    case IntID::ScrollSliderStyle:
+      aResult = eScrollThumbStyle_Proportional;
+      break;
+    case IntID::ScrollButtonLeftMouseButtonAction:
+      aResult = 0;
+      return NS_OK;
+    case IntID::ScrollButtonMiddleMouseButtonAction:
+      aResult = 3;
+      return NS_OK;
+    case IntID::ScrollButtonRightMouseButtonAction:
+      aResult = 3;
+      return NS_OK;
+    case IntID::TreeOpenDelay:
+      aResult = 1000;
+      break;
+    case IntID::TreeCloseDelay:
+      aResult = 1000;
+      break;
+    case IntID::TreeLazyScrollDelay:
+      aResult = 150;
+      break;
+    case IntID::TreeScrollDelay:
+      aResult = 100;
+      break;
+    case IntID::TreeScrollLinesMax:
+      aResult = 3;
+      break;
+    case IntID::TabFocusModel:
+      aResult = nsIContent::eTabFocus_textControlsMask;
+      break;
+    case IntID::ChosenMenuItemsShouldBlink:
+      aResult = 1;
+      break;
+    case IntID::WindowsAccentColorInTitlebar:
+    case IntID::WindowsDefaultTheme:
+    case IntID::DWMCompositor:
+      aResult = 0;
+      res = NS_ERROR_NOT_IMPLEMENTED;
+      break;
+    case IntID::WindowsClassic:
+    case IntID::WindowsGlass:
+      aResult = 0;
+      res = NS_ERROR_FAILURE;
+      break;
+    case IntID::TouchEnabled:
+    case IntID::MacGraphiteTheme:
+    case IntID::MacBigSurTheme:
+      aResult = 0;
+      res = NS_ERROR_NOT_IMPLEMENTED;
+      break;
+    case IntID::AlertNotificationOrigin:
+      aResult = NS_ALERT_TOP;
+      break;
+    case IntID::ScrollToClick:
+      aResult = 0;
+      break;
+    case IntID::IMERawInputUnderlineStyle:
+    case IntID::IMESelectedRawTextUnderlineStyle:
+    case IntID::IMEConvertedTextUnderlineStyle:
+    case IntID::IMESelectedConvertedTextUnderline:
+      aResult = NS_STYLE_TEXT_DECORATION_STYLE_SOLID;
+      break;
+    case IntID::SpellCheckerUnderlineStyle:
+      aResult = NS_STYLE_TEXT_DECORATION_STYLE_DOTTED;
+      break;
+    case IntID::MenuBarDrag:
+      aResult = 0;
+      break;
+    case IntID::WindowsThemeIdentifier:
+    case IntID::OperatingSystemVersionIdentifier:
+      aResult = 0;
+      res = NS_ERROR_NOT_IMPLEMENTED;
+      break;
+    case IntID::ScrollbarButtonAutoRepeatBehavior:
+      aResult = 0;
+      break;
+    case IntID::TooltipDelay:
+      aResult = 500;
+      break;
+    case IntID::SwipeAnimationEnabled:
+      aResult = 0;
+      break;
+    case IntID::ScrollbarDisplayOnMouseMove:
+      aResult = 0;
+      break;
+    case IntID::ScrollbarFadeBeginDelay:
+      aResult = 0;
+      break;
+    case IntID::ScrollbarFadeDuration:
+      aResult = 0;
+      break;
+    case IntID::ContextMenuOffsetVertical:
+      aResult = -6;
+      break;
+    case IntID::ContextMenuOffsetHorizontal:
+      aResult = 1;
+      break;
+    case IntID::GTKCSDAvailable:
+    case IntID::GTKCSDHideTitlebarByDefault:
+    case IntID::GTKCSDTransparentBackground:
+      aResult = 0;
+      break;
+    case IntID::GTKCSDMinimizeButton:
+      aResult = 0;
+      break;
+    case IntID::GTKCSDMaximizeButton:
+      aResult = 0;
+      break;
+    case IntID::GTKCSDCloseButton:
+      aResult = 1;
+      break;
+    case IntID::GTKCSDReversedPlacement:
+      aResult = 0;
+      break;
+    case IntID::SystemUsesDarkTheme:
+      aResult = 0;
+      break;
+    case IntID::PrefersReducedMotion:
+      aResult = 0;
+      break;
+    case IntID::PrimaryPointerCapabilities:
+      aResult = 0;
+      break;
+    case IntID::AllPointerCapabilities:
+      aResult = 0;
+      break;
+    default:
+      NS_WARNING(
+          "HeadlessLookAndFeel::NativeGetInt called with an unrecognized aID");
+      aResult = 0;
+      res = NS_ERROR_FAILURE;
+      break;
+  }
+  return res;
+}
+
+nsresult HeadlessLookAndFeel::NativeGetFloat(FloatID aID, float& aResult) {
+  nsresult res = NS_OK;
+
+  // Hardcoded values for GTK.
+  switch (aID) {
+    case FloatID::IMEUnderlineRelativeSize:
+      aResult = 1.0f;
+      break;
+    case FloatID::SpellCheckerUnderlineRelativeSize:
+      aResult = 1.0f;
+      break;
+    case FloatID::CaretAspectRatio:
+      // Intentionally failing to quietly indicate lack of support.
+      aResult = -1.0;
+      res = NS_ERROR_FAILURE;
+      break;
+    default:
+      NS_WARNING(
+          "HeadlessLookAndFeel::NativeGetFloat called with an unrecognized "
+          "aID");
+      aResult = -1.0;
+      res = NS_ERROR_FAILURE;
+      break;
+  }
+
+  return res;
+}
+
+bool HeadlessLookAndFeel::NativeGetFont(FontID aID, nsString& aFontName,
+                                        gfxFontStyle& aFontStyle) {
+  // Default to san-serif for everything.
+  aFontStyle.style = FontSlantStyle::Normal();
+  aFontStyle.weight = FontWeight::Normal();
+  aFontStyle.stretch = FontStretch::Normal();
+  aFontStyle.size = 14;
+  aFontStyle.systemFont = true;
+
+  aFontName.AssignLiteral("sans-serif");
+  return true;
+}
+
+char16_t HeadlessLookAndFeel::GetPasswordCharacterImpl() {
+  return UNICODE_BULLET;
+}
+
+void HeadlessLookAndFeel::RefreshImpl() { nsXPLookAndFeel::RefreshImpl(); }
+
+bool HeadlessLookAndFeel::GetEchoPasswordImpl() { return false; }
+
+}  // namespace widget
+}  // namespace mozilla
diff --git a/widget/headless/HeadlessScreenHelper.cpp b/widget/headless/HeadlessScreenHelper.cpp
new file mode 100644
index 0000000000..3800c9c73a
--- /dev/null
+++ b/widget/headless/HeadlessScreenHelper.cpp
@@ -0,0 +1,44 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "HeadlessScreenHelper.h"
+
+#include "prenv.h"
+#include "mozilla/dom/DOMTypes.h"
+#include "mozilla/RefPtr.h"
+#include "nsTArray.h"
+
+namespace mozilla {
+namespace widget {
+
+/* static */
+LayoutDeviceIntRect HeadlessScreenHelper::GetScreenRect() {
+  char* ev = PR_GetEnv("MOZ_HEADLESS_WIDTH");
+  int width = 1366;
+  if (ev) {
+    width = atoi(ev);
+  }
+  ev = PR_GetEnv("MOZ_HEADLESS_HEIGHT");
+  int height = 768;
+  if (ev) {
+    height = atoi(ev);
+  }
+  return LayoutDeviceIntRect(0, 0, width, height);
+}
+
+HeadlessScreenHelper::HeadlessScreenHelper() {
+  AutoTArray<RefPtr<Screen>, 1> screenList;
+  LayoutDeviceIntRect rect = GetScreenRect();
+  RefPtr<Screen> ret =
+      new Screen(rect, rect, 24, 24, DesktopToLayoutDeviceScale(),
+                 CSSToLayoutDeviceScale(), 96.0f);
+  screenList.AppendElement(ret.forget());
+  ScreenManager& screenManager = ScreenManager::GetSingleton();
+  screenManager.Refresh(std::move(screenList));
+}
+
+}  // namespace widget
+}  // namespace mozilla
diff --git a/widget/headless/HeadlessScreenHelper.h b/widget/headless/HeadlessScreenHelper.h
new file mode 100644
index 0000000000..f86677af52
--- /dev/null
+++ b/widget/headless/HeadlessScreenHelper.h
@@ -0,0 +1,27 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_widget_HeadlessScreenHelper_h
+#define mozilla_widget_HeadlessScreenHelper_h
+
+#include "mozilla/widget/ScreenManager.h"
+
+namespace mozilla {
+namespace widget {
+
+class HeadlessScreenHelper final : public ScreenManager::Helper {
+ public:
+  HeadlessScreenHelper();
+  ~HeadlessScreenHelper() override = default;
+
+ private:
+  static LayoutDeviceIntRect GetScreenRect();
+};
+
+}  // namespace widget
+}  // namespace mozilla
+
+#endif  // mozilla_widget_HeadlessScreenHelper_h
diff --git a/widget/headless/HeadlessSound.cpp b/widget/headless/HeadlessSound.cpp
new file mode 100644
index 0000000000..278d31b355
--- /dev/null
+++ b/widget/headless/HeadlessSound.cpp
@@ -0,0 +1,36 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "HeadlessSound.h"
+
+namespace mozilla {
+namespace widget {
+
+NS_IMPL_ISUPPORTS(HeadlessSound, nsISound, nsIStreamLoaderObserver)
+
+HeadlessSound::HeadlessSound() = default;
+
+HeadlessSound::~HeadlessSound() = default;
+
+NS_IMETHODIMP
+HeadlessSound::Init() { return NS_OK; }
+
+NS_IMETHODIMP HeadlessSound::OnStreamComplete(nsIStreamLoader* aLoader,
+                                              nsISupports* context,
+                                              nsresult aStatus,
+                                              uint32_t dataLen,
+                                              const uint8_t* data) {
+  return NS_OK;
+}
+
+NS_IMETHODIMP HeadlessSound::Beep() { return NS_OK; }
+
+NS_IMETHODIMP HeadlessSound::Play(nsIURL* aURL) { return NS_OK; }
+
+NS_IMETHODIMP HeadlessSound::PlayEventSound(uint32_t aEventId) { return NS_OK; }
+
+}  // namespace widget
+}  // namespace mozilla
diff --git a/widget/headless/HeadlessSound.h b/widget/headless/HeadlessSound.h
new file mode 100644
index 0000000000..a481acc61e
--- /dev/null
+++ b/widget/headless/HeadlessSound.h
@@ -0,0 +1,31 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_widget_HeadlessSound_h
+#define mozilla_widget_HeadlessSound_h
+
+#include "nsISound.h"
+#include "nsIStreamLoader.h"
+
+namespace mozilla {
+namespace widget {
+
+class HeadlessSound : public nsISound, public nsIStreamLoaderObserver {
+ public:
+  HeadlessSound();
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSISOUND
+  NS_DECL_NSISTREAMLOADEROBSERVER
+
+ private:
+  virtual ~HeadlessSound();
+};
+
+}  // namespace widget
+}  // namespace mozilla
+
+#endif  // mozilla_widget_HeadlessSound_h
diff --git a/widget/headless/HeadlessThemeGTK.cpp b/widget/headless/HeadlessThemeGTK.cpp
new file mode 100644
index 0000000000..64135202e4
--- /dev/null
+++ b/widget/headless/HeadlessThemeGTK.cpp
@@ -0,0 +1,417 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "HeadlessThemeGTK.h"
+
+#include "mozilla/StaticPrefs_layout.h"
+#include "nsStyleConsts.h"
+#include "nsIFrame.h"
+
+namespace mozilla {
+namespace widget {
+
+NS_IMPL_ISUPPORTS_INHERITED(HeadlessThemeGTK, nsNativeTheme, nsITheme)
+
+NS_IMETHODIMP
+HeadlessThemeGTK::DrawWidgetBackground(gfxContext* aContext, nsIFrame* aFrame,
+                                       StyleAppearance aAppearance,
+                                       const nsRect& aRect,
+                                       const nsRect& aDirtyRect) {
+  return NS_OK;
+}
+
+LayoutDeviceIntMargin HeadlessThemeGTK::GetWidgetBorder(
+    nsDeviceContext* aContext, nsIFrame* aFrame, StyleAppearance aAppearance) {
+  LayoutDeviceIntMargin result;
+  // The following values are generated from the Ubuntu GTK theme.
+  switch (aAppearance) {
+    case StyleAppearance::Button:
+    case StyleAppearance::Toolbarbutton:
+      result.top = 6;
+      result.right = 7;
+      result.bottom = 6;
+      result.left = 7;
+      break;
+    case StyleAppearance::FocusOutline:
+    case StyleAppearance::NumberInput:
+    case StyleAppearance::Textfield:
+      result.top = 5;
+      result.right = 7;
+      result.bottom = 5;
+      result.left = 7;
+      break;
+    case StyleAppearance::Statusbarpanel:
+    case StyleAppearance::Resizerpanel:
+    case StyleAppearance::Listbox:
+    case StyleAppearance::Treeview:
+    case StyleAppearance::Treeheadersortarrow:
+    case StyleAppearance::ProgressBar:
+    case StyleAppearance::SpinnerUpbutton:
+    case StyleAppearance::SpinnerDownbutton:
+    case StyleAppearance::SpinnerTextfield:
+    case StyleAppearance::Textarea:
+    case StyleAppearance::Menupopup:
+    case StyleAppearance::MozGtkInfoBar:
+      result.top = 1;
+      result.right = 1;
+      result.bottom = 1;
+      result.left = 1;
+      break;
+    case StyleAppearance::Treeheadercell:
+      result.top = 5;
+      result.right = 7;
+      result.bottom = 6;
+      result.left = 6;
+      break;
+    case StyleAppearance::Tab:
+      result.top = 4;
+      result.right = 7;
+      result.bottom = 2;
+      result.left = 7;
+      break;
+    case StyleAppearance::Tooltip:
+      result.top = 6;
+      result.right = 6;
+      result.bottom = 6;
+      result.left = 6;
+      break;
+    case StyleAppearance::MenulistButton:
+    case StyleAppearance::Menulist:
+      result.top = 6;
+      result.right = 22;
+      result.bottom = 6;
+      result.left = 7;
+      break;
+    case StyleAppearance::MozMenulistArrowButton:
+      result.top = 1;
+      result.right = 1;
+      result.bottom = 1;
+      result.left = 0;
+      break;
+    case StyleAppearance::Menuitem:
+    case StyleAppearance::Checkmenuitem:
+    case StyleAppearance::Radiomenuitem:
+      if (IsRegularMenuItem(aFrame)) {
+        break;
+      }
+      result.top = 3;
+      result.right = 5;
+      result.bottom = 3;
+      result.left = 5;
+      break;
+    default:
+      break;
+  }
+  return result;
+}
+
+bool HeadlessThemeGTK::GetWidgetPadding(nsDeviceContext* aContext,
+                                        nsIFrame* aFrame,
+                                        StyleAppearance aAppearance,
+                                        LayoutDeviceIntMargin* aResult) {
+  // The following values are generated from the Ubuntu GTK theme.
+  switch (aAppearance) {
+    case StyleAppearance::Radio:
+    case StyleAppearance::Checkbox:
+    case StyleAppearance::Toolbarbutton:
+    case StyleAppearance::Dualbutton:
+    case StyleAppearance::ToolbarbuttonDropdown:
+    case StyleAppearance::ButtonArrowUp:
+    case StyleAppearance::ButtonArrowDown:
+    case StyleAppearance::ButtonArrowNext:
+    case StyleAppearance::ButtonArrowPrevious:
+    case StyleAppearance::TabScrollArrowBack:
+    case StyleAppearance::TabScrollArrowForward:
+    case StyleAppearance::MozMenulistArrowButton:
+    case StyleAppearance::RangeThumb:
+    case StyleAppearance::ButtonFocus:
+      aResult->top = 0;
+      aResult->right = 0;
+      aResult->bottom = 0;
+      aResult->left = 0;
+      return true;
+    case StyleAppearance::Menuitem:
+    case StyleAppearance::Checkmenuitem:
+    case StyleAppearance::Radiomenuitem:
+      if (!IsRegularMenuItem(aFrame)) {
+        return false;
+      }
+      aResult->top = 3;
+      aResult->right = 5;
+      aResult->bottom = 3;
+      aResult->left = 5;
+      return true;
+    default:
+      break;
+  }
+  return false;
+}
+
+NS_IMETHODIMP
+HeadlessThemeGTK::GetMinimumWidgetSize(nsPresContext* aPresContext,
+                                       nsIFrame* aFrame,
+                                       StyleAppearance aAppearance,
+                                       LayoutDeviceIntSize* aResult,
+                                       bool* aIsOverridable) {
+  aResult->width = aResult->height = 0;
+  *aIsOverridable = true;
+
+  // The following values are generated from the Ubuntu GTK theme.
+  switch (aAppearance) {
+    case StyleAppearance::Splitter:
+      if (IsHorizontal(aFrame)) {
+        aResult->width = 6;
+        aResult->height = 0;
+      } else {
+        aResult->width = 0;
+        aResult->height = 6;
+      }
+      *aIsOverridable = false;
+      break;
+    case StyleAppearance::Button:
+    case StyleAppearance::Toolbarbutton:
+      aResult->width = 14;
+      aResult->height = 12;
+      break;
+    case StyleAppearance::Radio:
+    case StyleAppearance::Checkbox:
+      aResult->width = 18;
+      aResult->height = 18;
+      break;
+    case StyleAppearance::ToolbarbuttonDropdown:
+    case StyleAppearance::ButtonArrowUp:
+    case StyleAppearance::ButtonArrowDown:
+    case StyleAppearance::ButtonArrowNext:
+    case StyleAppearance::ButtonArrowPrevious:
+    case StyleAppearance::Resizer:
+      aResult->width = 15;
+      aResult->height = 15;
+      *aIsOverridable = false;
+      break;
+    case StyleAppearance::Separator:
+      aResult->width = 12;
+      aResult->height = 0;
+      break;
+    case StyleAppearance::Treetwisty:
+    case StyleAppearance::Treetwistyopen:
+      aResult->width = 8;
+      aResult->height = 8;
+      *aIsOverridable = false;
+      break;
+    case StyleAppearance::Treeheadercell:
+      aResult->width = 13;
+      aResult->height = 11;
+      break;
+    case StyleAppearance::Treeheadersortarrow:
+    case StyleAppearance::SpinnerUpbutton:
+    case StyleAppearance::SpinnerDownbutton:
+      aResult->width = 14;
+      aResult->height = 13;
+      break;
+    case StyleAppearance::TabScrollArrowBack:
+    case StyleAppearance::TabScrollArrowForward:
+      aResult->width = 16;
+      aResult->height = 16;
+      *aIsOverridable = false;
+      break;
+    case StyleAppearance::Spinner:
+      aResult->width = 14;
+      aResult->height = 26;
+      break;
+    case StyleAppearance::NumberInput:
+    case StyleAppearance::Textfield:
+      aResult->width = 0;
+      aResult->height = 12;
+      break;
+    case StyleAppearance::ScrollbarHorizontal:
+      aResult->width = 31;
+      aResult->height = 10;
+      break;
+    case StyleAppearance::ScrollbarVertical:
+      aResult->width = 10;
+      aResult->height = 31;
+      break;
+    case StyleAppearance::ScrollbarbuttonUp:
+    case StyleAppearance::ScrollbarbuttonDown:
+      aResult->width = 10;
+      aResult->height = 13;
+      *aIsOverridable = false;
+      break;
+    case StyleAppearance::ScrollbarbuttonLeft:
+    case StyleAppearance::ScrollbarbuttonRight:
+      aResult->width = 13;
+      aResult->height = 10;
+      *aIsOverridable = false;
+      break;
+    case StyleAppearance::ScrollbarthumbHorizontal:
+      aResult->width = 31;
+      aResult->height = 10;
+      *aIsOverridable = false;
+      break;
+    case StyleAppearance::ScrollbarthumbVertical:
+      aResult->width = 10;
+      aResult->height = 31;
+      *aIsOverridable = false;
+      break;
+    case StyleAppearance::MenulistButton:
+    case StyleAppearance::Menulist:
+      aResult->width = 44;
+      aResult->height = 27;
+      break;
+    case StyleAppearance::MozMenulistArrowButton:
+      aResult->width = 29;
+      aResult->height = 28;
+      *aIsOverridable = false;
+      break;
+    case StyleAppearance::RangeThumb:
+      aResult->width = 14;
+      aResult->height = 18;
+      *aIsOverridable = false;
+      break;
+    case StyleAppearance::Menuseparator:
+      aResult->width = 0;
+      aResult->height = 8;
+      *aIsOverridable = false;
+      break;
+    default:
+      break;
+  }
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+HeadlessThemeGTK::WidgetStateChanged(nsIFrame* aFrame,
+                                     StyleAppearance aAppearance,
+                                     nsAtom* aAttribute, bool* aShouldRepaint,
+                                     const nsAttrValue* aOldValue) {
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+HeadlessThemeGTK::ThemeChanged() { return NS_OK; }
+
+static bool IsFrameContentNodeInNamespace(nsIFrame* aFrame,
+                                          uint32_t aNamespace) {
+  nsIContent* content = aFrame ? aFrame->GetContent() : nullptr;
+  if (!content) return false;
+  return content->IsInNamespace(aNamespace);
+}
+
+NS_IMETHODIMP_(bool)
+HeadlessThemeGTK::ThemeSupportsWidget(nsPresContext* aPresContext,
+                                      nsIFrame* aFrame,
+                                      StyleAppearance aAppearance) {
+  switch (aAppearance) {
+    case StyleAppearance::Button:
+    case StyleAppearance::Radio:
+    case StyleAppearance::Checkbox:
+    case StyleAppearance::FocusOutline:
+    case StyleAppearance::Toolbox:
+    case StyleAppearance::Toolbar:
+    case StyleAppearance::Toolbarbutton:
+    case StyleAppearance::Dualbutton:
+    case StyleAppearance::ToolbarbuttonDropdown:
+    case StyleAppearance::ButtonArrowUp:
+    case StyleAppearance::ButtonArrowDown:
+    case StyleAppearance::ButtonArrowNext:
+    case StyleAppearance::ButtonArrowPrevious:
+    case StyleAppearance::Separator:
+    case StyleAppearance::Toolbargripper:
+    case StyleAppearance::Splitter:
+    case StyleAppearance::Statusbar:
+    case StyleAppearance::Statusbarpanel:
+    case StyleAppearance::Resizerpanel:
+    case StyleAppearance::Resizer:
+    case StyleAppearance::Listbox:
+    case StyleAppearance::Treeview:
+    case StyleAppearance::Treetwisty:
+    case StyleAppearance::Treeheadercell:
+    case StyleAppearance::Treeheadersortarrow:
+    case StyleAppearance::Treetwistyopen:
+    case StyleAppearance::ProgressBar:
+    case StyleAppearance::Progresschunk:
+    case StyleAppearance::Tab:
+    case StyleAppearance::Tabpanels:
+    case StyleAppearance::TabScrollArrowBack:
+    case StyleAppearance::TabScrollArrowForward:
+    case StyleAppearance::Tooltip:
+    case StyleAppearance::Spinner:
+    case StyleAppearance::SpinnerUpbutton:
+    case StyleAppearance::SpinnerDownbutton:
+    case StyleAppearance::SpinnerTextfield:
+    case StyleAppearance::NumberInput:
+    case StyleAppearance::ScrollbarHorizontal:
+    case StyleAppearance::ScrollbarVertical:
+    case StyleAppearance::ScrollbarbuttonUp:
+    case StyleAppearance::ScrollbarbuttonDown:
+    case StyleAppearance::ScrollbarbuttonLeft:
+    case StyleAppearance::ScrollbarbuttonRight:
+    case StyleAppearance::ScrollbartrackHorizontal:
+    case StyleAppearance::ScrollbartrackVertical:
+    case StyleAppearance::ScrollbarthumbHorizontal:
+    case StyleAppearance::ScrollbarthumbVertical:
+    case StyleAppearance::Textfield:
+    case StyleAppearance::Textarea:
+    case StyleAppearance::Menulist:
+    case StyleAppearance::MenulistButton:
+    case StyleAppearance::MenulistText:
+    case StyleAppearance::Range:
+    case StyleAppearance::RangeThumb:
+    case StyleAppearance::CheckboxContainer:
+    case StyleAppearance::RadioContainer:
+    case StyleAppearance::CheckboxLabel:
+    case StyleAppearance::RadioLabel:
+    case StyleAppearance::ButtonFocus:
+    case StyleAppearance::Window:
+    case StyleAppearance::Dialog:
+    case StyleAppearance::Menubar:
+    case StyleAppearance::Menupopup:
+    case StyleAppearance::Menuitem:
+    case StyleAppearance::Checkmenuitem:
+    case StyleAppearance::Radiomenuitem:
+    case StyleAppearance::Menuseparator:
+    case StyleAppearance::Menuarrow:
+    case StyleAppearance::MozGtkInfoBar:
+      return !IsWidgetStyled(aPresContext, aFrame, aAppearance);
+    case StyleAppearance::MozMenulistArrowButton:
+      return (!aFrame ||
+              IsFrameContentNodeInNamespace(aFrame, kNameSpaceID_XUL)) &&
+             !IsWidgetStyled(aPresContext, aFrame, aAppearance);
+    default:
+      break;
+  }
+  return false;
+}
+
+NS_IMETHODIMP_(bool)
+HeadlessThemeGTK::WidgetIsContainer(StyleAppearance aAppearance) {
+  if (aAppearance == StyleAppearance::MozMenulistArrowButton ||
+      aAppearance == StyleAppearance::Radio ||
+      aAppearance == StyleAppearance::RangeThumb ||
+      aAppearance == StyleAppearance::Checkbox ||
+      aAppearance == StyleAppearance::TabScrollArrowBack ||
+      aAppearance == StyleAppearance::TabScrollArrowForward ||
+      aAppearance == StyleAppearance::ButtonArrowUp ||
+      aAppearance == StyleAppearance::ButtonArrowDown ||
+      aAppearance == StyleAppearance::ButtonArrowNext ||
+      aAppearance == StyleAppearance::ButtonArrowPrevious) {
+    return false;
+  }
+  return true;
+}
+
+bool HeadlessThemeGTK::ThemeDrawsFocusForWidget(StyleAppearance aAppearance) {
+  if (aAppearance == StyleAppearance::Menulist ||
+      aAppearance == StyleAppearance::Button ||
+      aAppearance == StyleAppearance::Treeheadercell) {
+    return true;
+  }
+  return false;
+}
+
+bool HeadlessThemeGTK::ThemeNeedsComboboxDropmarker() { return false; }
+
+}  // namespace widget
+}  // namespace mozilla
diff --git a/widget/headless/HeadlessThemeGTK.h b/widget/headless/HeadlessThemeGTK.h
new file mode 100644
index 0000000000..11ca0a1f92
--- /dev/null
+++ b/widget/headless/HeadlessThemeGTK.h
@@ -0,0 +1,61 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_widget_HeadlessThemeGTK_h
+#define mozilla_widget_HeadlessThemeGTK_h
+
+#include "nsITheme.h"
+#include "nsNativeTheme.h"
+
+namespace mozilla {
+namespace widget {
+
+class HeadlessThemeGTK final : private nsNativeTheme, public nsITheme {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+
+  HeadlessThemeGTK() = default;
+  NS_IMETHOD DrawWidgetBackground(gfxContext* aContext, nsIFrame* aFrame,
+                                  StyleAppearance aAppearance,
+                                  const nsRect& aRect,
+                                  const nsRect& aDirtyRect) override;
+
+  [[nodiscard]] LayoutDeviceIntMargin GetWidgetBorder(
+      nsDeviceContext* aContext, nsIFrame* aFrame,
+      StyleAppearance aAppearance) override;
+
+  bool GetWidgetPadding(nsDeviceContext* aContext, nsIFrame* aFrame,
+                        StyleAppearance aAppearance,
+                        LayoutDeviceIntMargin* aResult) override;
+  NS_IMETHOD GetMinimumWidgetSize(nsPresContext* aPresContext, nsIFrame* aFrame,
+                                  StyleAppearance aAppearance,
+                                  mozilla::LayoutDeviceIntSize* aResult,
+                                  bool* aIsOverridable) override;
+
+  NS_IMETHOD WidgetStateChanged(nsIFrame* aFrame, StyleAppearance aAppearance,
+                                nsAtom* aAttribute, bool* aShouldRepaint,
+                                const nsAttrValue* aOldValue) override;
+
+  NS_IMETHOD ThemeChanged() override;
+
+  NS_IMETHOD_(bool)
+  ThemeSupportsWidget(nsPresContext* aPresContext, nsIFrame* aFrame,
+                      StyleAppearance aAppearance) override;
+
+  NS_IMETHOD_(bool) WidgetIsContainer(StyleAppearance aAppearance) override;
+
+  NS_IMETHOD_(bool)
+  ThemeDrawsFocusForWidget(StyleAppearance aAppearance) override;
+
+  virtual bool ThemeNeedsComboboxDropmarker() override;
+
+ protected:
+  virtual ~HeadlessThemeGTK() = default;
+};
+
+}  // namespace widget
+}  // namespace mozilla
+
+#endif  // mozilla_widget_HeadlessThemeGTK_h
diff --git a/widget/headless/HeadlessWidget.cpp b/widget/headless/HeadlessWidget.cpp
new file mode 100644
index 0000000000..f4f3acda7e
--- /dev/null
+++ b/widget/headless/HeadlessWidget.cpp
@@ -0,0 +1,503 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#include "HeadlessWidget.h"
+#include "HeadlessCompositorWidget.h"
+#include "Layers.h"
+#include "BasicLayers.h"
+#include "BasicEvents.h"
+#include "MouseEvents.h"
+#include "mozilla/gfx/gfxVars.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/TextEvents.h"
+#include "mozilla/widget/HeadlessWidgetTypes.h"
+#include "mozilla/widget/PlatformWidgetTypes.h"
+#include "nsIScreen.h"
+#include "HeadlessKeyBindings.h"
+
+using namespace mozilla;
+using namespace mozilla::gfx;
+using namespace mozilla::layers;
+
+using mozilla::LogLevel;
+
+#ifdef MOZ_LOGGING
+
+#  include "mozilla/Logging.h"
+static mozilla::LazyLogModule sWidgetLog("Widget");
+static mozilla::LazyLogModule sWidgetFocusLog("WidgetFocus");
+#  define LOG(args) MOZ_LOG(sWidgetLog, mozilla::LogLevel::Debug, args)
+#  define LOGFOCUS(args) \
+    MOZ_LOG(sWidgetFocusLog, mozilla::LogLevel::Debug, args)
+
+#else
+
+#  define LOG(args)
+#  define LOGFOCUS(args)
+
+#endif /* MOZ_LOGGING */
+
+/*static*/
+already_AddRefed<nsIWidget> nsIWidget::CreateHeadlessWidget() {
+  nsCOMPtr<nsIWidget> widget = new mozilla::widget::HeadlessWidget();
+  return widget.forget();
+}
+
+namespace mozilla {
+namespace widget {
+
+StaticAutoPtr<nsTArray<HeadlessWidget*>> HeadlessWidget::sActiveWindows;
+
+already_AddRefed<HeadlessWidget> HeadlessWidget::GetActiveWindow() {
+  if (!sActiveWindows) {
+    return nullptr;
+  }
+  auto length = sActiveWindows->Length();
+  if (length == 0) {
+    return nullptr;
+  }
+  RefPtr<HeadlessWidget> widget = sActiveWindows->ElementAt(length - 1);
+  return widget.forget();
+}
+
+HeadlessWidget::HeadlessWidget()
+    : mEnabled(true),
+      mVisible(false),
+      mDestroyed(false),
+      mTopLevel(nullptr),
+      mCompositorWidget(nullptr),
+      mLastSizeMode(nsSizeMode_Normal),
+      mEffectiveSizeMode(nsSizeMode_Normal),
+      mRestoreBounds(0, 0, 0, 0) {
+  if (!sActiveWindows) {
+    sActiveWindows = new nsTArray<HeadlessWidget*>();
+    ClearOnShutdown(&sActiveWindows);
+  }
+}
+
+HeadlessWidget::~HeadlessWidget() {
+  LOG(("HeadlessWidget::~HeadlessWidget() [%p]\n", (void*)this));
+
+  Destroy();
+}
+
+void HeadlessWidget::Destroy() {
+  if (mDestroyed) {
+    return;
+  }
+  LOG(("HeadlessWidget::Destroy [%p]\n", (void*)this));
+  mDestroyed = true;
+
+  if (sActiveWindows) {
+    int32_t index = sActiveWindows->IndexOf(this);
+    if (index != -1) {
+      RefPtr<HeadlessWidget> activeWindow = GetActiveWindow();
+      sActiveWindows->RemoveElementAt(index);
+      // If this is the currently active widget and there's a previously active
+      // widget, activate the previous widget.
+      RefPtr<HeadlessWidget> previousActiveWindow = GetActiveWindow();
+      if (this == activeWindow && previousActiveWindow &&
+          previousActiveWindow->mWidgetListener) {
+        previousActiveWindow->mWidgetListener->WindowActivated();
+      }
+    }
+  }
+
+  nsBaseWidget::OnDestroy();
+
+  nsBaseWidget::Destroy();
+}
+
+nsresult HeadlessWidget::Create(nsIWidget* aParent,
+                                nsNativeWidget aNativeParent,
+                                const LayoutDeviceIntRect& aRect,
+                                nsWidgetInitData* aInitData) {
+  MOZ_ASSERT(!aNativeParent, "No native parents for headless widgets.");
+
+  BaseCreate(nullptr, aInitData);
+
+  mBounds = aRect;
+  mRestoreBounds = aRect;
+
+  if (aParent) {
+    mTopLevel = aParent->GetTopLevelWidget();
+  } else {
+    mTopLevel = this;
+  }
+
+  return NS_OK;
+}
+
+already_AddRefed<nsIWidget> HeadlessWidget::CreateChild(
+    const LayoutDeviceIntRect& aRect, nsWidgetInitData* aInitData,
+    bool aForceUseIWidgetParent) {
+  nsCOMPtr<nsIWidget> widget = nsIWidget::CreateHeadlessWidget();
+  if (!widget) {
+    return nullptr;
+  }
+  if (NS_FAILED(widget->Create(this, nullptr, aRect, aInitData))) {
+    return nullptr;
+  }
+  return widget.forget();
+}
+
+void HeadlessWidget::GetCompositorWidgetInitData(
+    mozilla::widget::CompositorWidgetInitData* aInitData) {
+  *aInitData =
+      mozilla::widget::HeadlessCompositorWidgetInitData(GetClientSize());
+}
+
+nsIWidget* HeadlessWidget::GetTopLevelWidget() { return mTopLevel; }
+
+void HeadlessWidget::RaiseWindow() {
+  MOZ_ASSERT(mTopLevel == this || mWindowType == eWindowType_dialog ||
+                 mWindowType == eWindowType_sheet,
+             "Raising a non-toplevel window.");
+
+  // Do nothing if this is the currently active window.
+  RefPtr<HeadlessWidget> activeWindow = GetActiveWindow();
+  if (activeWindow == this) {
+    return;
+  }
+
+  // Raise the window to the top of the stack.
+  nsWindowZ placement = nsWindowZTop;
+  nsCOMPtr<nsIWidget> actualBelow;
+  if (mWidgetListener)
+    mWidgetListener->ZLevelChanged(true, &placement, nullptr,
+                                   getter_AddRefs(actualBelow));
+
+  // Deactivate the last active window.
+  if (activeWindow && activeWindow->mWidgetListener) {
+    activeWindow->mWidgetListener->WindowDeactivated();
+  }
+
+  // Remove this window if it's already tracked.
+  int32_t index = sActiveWindows->IndexOf(this);
+  if (index != -1) {
+    sActiveWindows->RemoveElementAt(index);
+  }
+
+  // Activate this window.
+  sActiveWindows->AppendElement(this);
+  if (mWidgetListener) mWidgetListener->WindowActivated();
+}
+
+void HeadlessWidget::Show(bool aState) {
+  mVisible = aState;
+
+  LOG(("HeadlessWidget::Show [%p] state %d\n", (void*)this, aState));
+
+  // Top-level window and dialogs are activated/raised when shown.
+  if (aState && (mTopLevel == this || mWindowType == eWindowType_dialog ||
+                 mWindowType == eWindowType_sheet)) {
+    RaiseWindow();
+  }
+
+  ApplySizeModeSideEffects();
+}
+
+bool HeadlessWidget::IsVisible() const { return mVisible; }
+
+void HeadlessWidget::SetFocus(Raise aRaise,
+                              mozilla::dom::CallerType aCallerType) {
+  LOGFOCUS(("  SetFocus %d [%p]\n", aRaise == Raise::Yes, (void*)this));
+
+  // This means we request activation of our toplevel window.
+  if (aRaise == Raise::Yes) {
+    HeadlessWidget* topLevel = (HeadlessWidget*)GetTopLevelWidget();
+
+    // The toplevel only becomes active if it's currently visible; otherwise, it
+    // will be activated anyway when it's shown.
+    if (topLevel->IsVisible()) topLevel->RaiseWindow();
+  }
+}
+
+void HeadlessWidget::Enable(bool aState) { mEnabled = aState; }
+
+bool HeadlessWidget::IsEnabled() const { return mEnabled; }
+
+void HeadlessWidget::Move(double aX, double aY) {
+  LOG(("HeadlessWidget::Move [%p] %f %f\n", (void*)this, aX, aY));
+
+  double scale =
+      BoundsUseDesktopPixels() ? GetDesktopToDeviceScale().scale : 1.0;
+  int32_t x = NSToIntRound(aX * scale);
+  int32_t y = NSToIntRound(aY * scale);
+
+  if (mWindowType == eWindowType_toplevel ||
+      mWindowType == eWindowType_dialog) {
+    SetSizeMode(nsSizeMode_Normal);
+  }
+
+  // Since a popup window's x/y coordinates are in relation to
+  // the parent, the parent might have moved so we always move a
+  // popup window.
+  if (mBounds.IsEqualXY(x, y) && mWindowType != eWindowType_popup) {
+    return;
+  }
+
+  mBounds.MoveTo(x, y);
+  NotifyRollupGeometryChange();
+}
+
+LayoutDeviceIntPoint HeadlessWidget::WidgetToScreenOffset() {
+  return mTopLevel->GetBounds().TopLeft();
+}
+
+LayerManager* HeadlessWidget::GetLayerManager(
+    PLayerTransactionChild* aShadowManager, LayersBackend aBackendHint,
+    LayerManagerPersistence aPersistence) {
+  return nsBaseWidget::GetLayerManager(aShadowManager, aBackendHint,
+                                       aPersistence);
+}
+
+void HeadlessWidget::SetCompositorWidgetDelegate(
+    CompositorWidgetDelegate* delegate) {
+  if (delegate) {
+    mCompositorWidget = delegate->AsHeadlessCompositorWidget();
+    MOZ_ASSERT(mCompositorWidget,
+               "HeadlessWidget::SetCompositorWidgetDelegate called with a "
+               "non-HeadlessCompositorWidget");
+  } else {
+    mCompositorWidget = nullptr;
+  }
+}
+
+void HeadlessWidget::Resize(double aWidth, double aHeight, bool aRepaint) {
+  int32_t width = NSToIntRound(aWidth);
+  int32_t height = NSToIntRound(aHeight);
+  ConstrainSize(&width, &height);
+  mBounds.SizeTo(LayoutDeviceIntSize(width, height));
+
+  if (mCompositorWidget) {
+    mCompositorWidget->NotifyClientSizeChanged(
+        LayoutDeviceIntSize(mBounds.Width(), mBounds.Height()));
+  }
+  if (mWidgetListener) {
+    mWidgetListener->WindowResized(this, mBounds.Width(), mBounds.Height());
+  }
+  if (mAttachedWidgetListener) {
+    mAttachedWidgetListener->WindowResized(this, mBounds.Width(),
+                                           mBounds.Height());
+  }
+}
+
+void HeadlessWidget::Resize(double aX, double aY, double aWidth, double aHeight,
+                            bool aRepaint) {
+  if (!mBounds.IsEqualXY(aX, aY)) {
+    NotifyWindowMoved(aX, aY);
+  }
+  return Resize(aWidth, aHeight, aRepaint);
+}
+
+void HeadlessWidget::SetSizeMode(nsSizeMode aMode) {
+  LOG(("HeadlessWidget::SetSizeMode [%p] %d\n", (void*)this, aMode));
+
+  if (aMode == mSizeMode) {
+    return;
+  }
+
+  nsBaseWidget::SetSizeMode(aMode);
+
+  // Normally in real widget backends a window event would be triggered that
+  // would cause the window manager to handle resizing the window. In headless
+  // the window must manually be resized.
+  ApplySizeModeSideEffects();
+}
+
+void HeadlessWidget::ApplySizeModeSideEffects() {
+  if (!mVisible || mEffectiveSizeMode == mSizeMode) {
+    return;
+  }
+
+  if (mEffectiveSizeMode == nsSizeMode_Normal) {
+    // Store the last normal size bounds so it can be restored when entering
+    // normal mode again.
+    mRestoreBounds = mBounds;
+  }
+
+  switch (mSizeMode) {
+    case nsSizeMode_Normal: {
+      Resize(mRestoreBounds.X(), mRestoreBounds.Y(), mRestoreBounds.Width(),
+             mRestoreBounds.Height(), false);
+      break;
+    }
+    case nsSizeMode_Minimized:
+      break;
+    case nsSizeMode_Maximized: {
+      nsCOMPtr<nsIScreen> screen = GetWidgetScreen();
+      if (screen) {
+        int32_t left, top, width, height;
+        if (NS_SUCCEEDED(
+                screen->GetRectDisplayPix(&left, &top, &width, &height))) {
+          Resize(0, 0, width, height, true);
+        }
+      }
+      break;
+    }
+    case nsSizeMode_Fullscreen:
+      // This will take care of resizing the window.
+      nsBaseWidget::InfallibleMakeFullScreen(true);
+      break;
+    default:
+      break;
+  }
+
+  mEffectiveSizeMode = mSizeMode;
+  if (mWidgetListener) {
+    mWidgetListener->SizeModeChanged(mSizeMode);
+  }
+}
+
+nsresult HeadlessWidget::MakeFullScreen(bool aFullScreen,
+                                        nsIScreen* aTargetScreen) {
+  // Directly update the size mode here so a later call SetSizeMode does
+  // nothing.
+  if (aFullScreen) {
+    if (mSizeMode != nsSizeMode_Fullscreen) {
+      mLastSizeMode = mSizeMode;
+    }
+    mSizeMode = nsSizeMode_Fullscreen;
+  } else {
+    mSizeMode = mLastSizeMode;
+  }
+
+  // Notify the listener first so size mode change events are triggered before
+  // resize events.
+  if (mWidgetListener) {
+    mWidgetListener->SizeModeChanged(mSizeMode);
+    mWidgetListener->FullscreenChanged(aFullScreen);
+  }
+
+  // Real widget backends don't seem to follow a common approach for
+  // when and how many resize events are triggered during fullscreen
+  // transitions. InfallibleMakeFullScreen will trigger a resize, but it
+  // will be ignored if still transitioning to fullscreen, so it must be
+  // triggered on the next tick.
+  RefPtr<HeadlessWidget> self(this);
+  nsCOMPtr<nsIScreen> targetScreen(aTargetScreen);
+  NS_DispatchToCurrentThread(NS_NewRunnableFunction(
+      "HeadlessWidget::MakeFullScreen",
+      [self, targetScreen, aFullScreen]() -> void {
+        self->InfallibleMakeFullScreen(aFullScreen, targetScreen);
+      }));
+
+  return NS_OK;
+}
+
+nsresult HeadlessWidget::AttachNativeKeyEvent(WidgetKeyboardEvent& aEvent) {
+  HeadlessKeyBindings& bindings = HeadlessKeyBindings::GetInstance();
+  return bindings.AttachNativeKeyEvent(aEvent);
+}
+
+bool HeadlessWidget::GetEditCommands(NativeKeyBindingsType aType,
+                                     const WidgetKeyboardEvent& aEvent,
+                                     nsTArray<CommandInt>& aCommands) {
+  // Validate the arguments.
+  if (NS_WARN_IF(!nsIWidget::GetEditCommands(aType, aEvent, aCommands))) {
+    return false;
+  }
+
+  HeadlessKeyBindings& bindings = HeadlessKeyBindings::GetInstance();
+  bindings.GetEditCommands(aType, aEvent, aCommands);
+  return true;
+}
+
+nsresult HeadlessWidget::DispatchEvent(WidgetGUIEvent* aEvent,
+                                       nsEventStatus& aStatus) {
+#ifdef DEBUG
+  debug_DumpEvent(stdout, aEvent->mWidget, aEvent, "HeadlessWidget", 0);
+#endif
+
+  aStatus = nsEventStatus_eIgnore;
+
+  if (mAttachedWidgetListener) {
+    aStatus = mAttachedWidgetListener->HandleEvent(aEvent, mUseAttachedEvents);
+  } else if (mWidgetListener) {
+    aStatus = mWidgetListener->HandleEvent(aEvent, mUseAttachedEvents);
+  }
+
+  return NS_OK;
+}
+
+nsresult HeadlessWidget::SynthesizeNativeMouseEvent(LayoutDeviceIntPoint aPoint,
+                                                    uint32_t aNativeMessage,
+                                                    uint32_t aModifierFlags,
+                                                    nsIObserver* aObserver) {
+  AutoObserverNotifier notifier(aObserver, "mouseevent");
+  EventMessage msg;
+  switch (aNativeMessage) {
+    case MOZ_HEADLESS_MOUSE_MOVE:
+      msg = eMouseMove;
+      break;
+    case MOZ_HEADLESS_MOUSE_DOWN:
+      msg = eMouseDown;
+      break;
+    case MOZ_HEADLESS_MOUSE_UP:
+      msg = eMouseUp;
+      break;
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unsupported synthesized mouse event");
+      return NS_ERROR_UNEXPECTED;
+  }
+  WidgetMouseEvent event(true, msg, this, WidgetMouseEvent::eReal);
+  event.mRefPoint = aPoint - WidgetToScreenOffset();
+  if (msg == eMouseDown || msg == eMouseUp) {
+    event.mButton = MouseButton::ePrimary;
+  }
+  if (msg == eMouseDown) {
+    event.mClickCount = 1;
+  }
+  event.AssignEventTime(WidgetEventTime());
+  DispatchInputEvent(&event);
+  return NS_OK;
+}
+
+nsresult HeadlessWidget::SynthesizeNativeMouseScrollEvent(
+    mozilla::LayoutDeviceIntPoint aPoint, uint32_t aNativeMessage,
+    double aDeltaX, double aDeltaY, double aDeltaZ, uint32_t aModifierFlags,
+    uint32_t aAdditionalFlags, nsIObserver* aObserver) {
+  AutoObserverNotifier notifier(aObserver, "mousescrollevent");
+  printf(">>> DEBUG_ME: Synth: aDeltaY=%f\n", aDeltaY);
+  // The various platforms seem to handle scrolling deltas differently,
+  // but the following seems to emulate it well enough.
+  WidgetWheelEvent event(true, eWheel, this);
+  event.mDeltaMode = MOZ_HEADLESS_SCROLL_DELTA_MODE;
+  event.mIsNoLineOrPageDelta = true;
+  event.mDeltaX = -aDeltaX * MOZ_HEADLESS_SCROLL_MULTIPLIER;
+  event.mDeltaY = -aDeltaY * MOZ_HEADLESS_SCROLL_MULTIPLIER;
+  event.mDeltaZ = -aDeltaZ * MOZ_HEADLESS_SCROLL_MULTIPLIER;
+  event.mRefPoint = aPoint - WidgetToScreenOffset();
+  event.AssignEventTime(WidgetEventTime());
+  DispatchInputEvent(&event);
+  return NS_OK;
+}
+
+nsresult HeadlessWidget::SynthesizeNativeTouchPoint(
+    uint32_t aPointerId, TouchPointerState aPointerState,
+    LayoutDeviceIntPoint aPoint, double aPointerPressure,
+    uint32_t aPointerOrientation, nsIObserver* aObserver) {
+  AutoObserverNotifier notifier(aObserver, "touchpoint");
+
+  MOZ_ASSERT(NS_IsMainThread());
+  if (aPointerState == TOUCH_HOVER) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  if (!mSynthesizedTouchInput) {
+    mSynthesizedTouchInput = MakeUnique<MultiTouchInput>();
+  }
+
+  LayoutDeviceIntPoint pointInWindow = aPoint - WidgetToScreenOffset();
+  MultiTouchInput inputToDispatch = UpdateSynthesizedTouchState(
+      mSynthesizedTouchInput.get(), PR_IntervalNow(), TimeStamp::Now(),
+      aPointerId, aPointerState, pointInWindow, aPointerPressure,
+      aPointerOrientation);
+  DispatchTouchInput(inputToDispatch);
+  return NS_OK;
+}
+
+}  // namespace widget
+}  // namespace mozilla
diff --git a/widget/headless/HeadlessWidget.h b/widget/headless/HeadlessWidget.h
new file mode 100644
index 0000000000..25cb1623ba
--- /dev/null
+++ b/widget/headless/HeadlessWidget.h
@@ -0,0 +1,187 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef HEADLESSWIDGET_H
+#define HEADLESSWIDGET_H
+
+#include "mozilla/widget/InProcessCompositorWidget.h"
+#include "nsBaseWidget.h"
+#include "CompositorWidget.h"
+#include "mozilla/dom/WheelEventBinding.h"
+
+// The various synthesized event values are hardcoded to avoid pulling
+// in the platform specific widget code.
+#if defined(MOZ_WIDGET_GTK)
+#  define MOZ_HEADLESS_MOUSE_MOVE 3  // GDK_MOTION_NOTIFY
+#  define MOZ_HEADLESS_MOUSE_DOWN 4  // GDK_BUTTON_PRESS
+#  define MOZ_HEADLESS_MOUSE_UP 7    // GDK_BUTTON_RELEASE
+#  define MOZ_HEADLESS_SCROLL_MULTIPLIER 3
+#  define MOZ_HEADLESS_SCROLL_DELTA_MODE \
+    mozilla::dom::WheelEvent_Binding::DOM_DELTA_LINE
+#elif defined(XP_WIN)
+#  define MOZ_HEADLESS_MOUSE_MOVE 1  // MOUSEEVENTF_MOVE
+#  define MOZ_HEADLESS_MOUSE_DOWN 2  // MOUSEEVENTF_LEFTDOWN
+#  define MOZ_HEADLESS_MOUSE_UP 4    // MOUSEEVENTF_LEFTUP
+#  define MOZ_HEADLESS_SCROLL_MULTIPLIER \
+    .025  // default scroll lines (3) / WHEEL_DELTA (120)
+#  define MOZ_HEADLESS_SCROLL_DELTA_MODE \
+    mozilla::dom::WheelEvent_Binding::DOM_DELTA_LINE
+#elif defined(XP_MACOSX)
+#  define MOZ_HEADLESS_MOUSE_MOVE 5  // NSEventTypeMouseMoved
+#  define MOZ_HEADLESS_MOUSE_DOWN 1  // NSEventTypeLeftMouseDown
+#  define MOZ_HEADLESS_MOUSE_UP 2    // NSEventTypeLeftMouseUp
+#  define MOZ_HEADLESS_SCROLL_MULTIPLIER 1
+#  define MOZ_HEADLESS_SCROLL_DELTA_MODE \
+    mozilla::dom::WheelEvent_Binding::DOM_DELTA_PIXEL
+#elif defined(ANDROID)
+#  define MOZ_HEADLESS_MOUSE_MOVE 7  // ACTION_HOVER_MOVE
+#  define MOZ_HEADLESS_MOUSE_DOWN 5  // ACTION_POINTER_DOWN
+#  define MOZ_HEADLESS_MOUSE_UP 6    // ACTION_POINTER_UP
+#  define MOZ_HEADLESS_SCROLL_MULTIPLIER 1
+#  define MOZ_HEADLESS_SCROLL_DELTA_MODE \
+    mozilla::dom::WheelEvent_Binding::DOM_DELTA_LINE
+#else
+#  define MOZ_HEADLESS_MOUSE_MOVE -1
+#  define MOZ_HEADLESS_MOUSE_DOWN -1
+#  define MOZ_HEADLESS_MOUSE_UP -1
+#  define MOZ_HEADLESS_SCROLL_MULTIPLIER -1
+#  define MOZ_HEADLESS_SCROLL_DELTA_MODE -1
+#endif
+
+namespace mozilla {
+namespace widget {
+
+class HeadlessWidget : public nsBaseWidget {
+ public:
+  HeadlessWidget();
+
+  NS_INLINE_DECL_REFCOUNTING_INHERITED(HeadlessWidget, nsBaseWidget)
+
+  void* GetNativeData(uint32_t aDataType) override {
+    // Headless widgets have no native data.
+    return nullptr;
+  }
+
+  virtual nsresult Create(nsIWidget* aParent, nsNativeWidget aNativeParent,
+                          const LayoutDeviceIntRect& aRect,
+                          nsWidgetInitData* aInitData = nullptr) override;
+  using nsBaseWidget::Create;  // for Create signature not overridden here
+  virtual already_AddRefed<nsIWidget> CreateChild(
+      const LayoutDeviceIntRect& aRect, nsWidgetInitData* aInitData = nullptr,
+      bool aForceUseIWidgetParent = false) override;
+
+  virtual nsIWidget* GetTopLevelWidget() override;
+
+  virtual void GetCompositorWidgetInitData(
+      mozilla::widget::CompositorWidgetInitData* aInitData) override;
+
+  virtual void Destroy() override;
+  virtual void Show(bool aState) override;
+  virtual bool IsVisible() const override;
+  virtual void Move(double aX, double aY) override;
+  virtual void Resize(double aWidth, double aHeight, bool aRepaint) override;
+  virtual void Resize(double aX, double aY, double aWidth, double aHeight,
+                      bool aRepaint) override;
+  virtual void SetSizeMode(nsSizeMode aMode) override;
+  virtual nsresult MakeFullScreen(bool aFullScreen,
+                                  nsIScreen* aTargetScreen = nullptr) override;
+  virtual void Enable(bool aState) override;
+  virtual bool IsEnabled() const override;
+  virtual void SetFocus(Raise, mozilla::dom::CallerType aCallerType) override;
+  virtual nsresult ConfigureChildren(
+      const nsTArray<Configuration>& aConfigurations) override {
+    MOZ_ASSERT_UNREACHABLE(
+        "Headless widgets do not support configuring children.");
+    return NS_ERROR_FAILURE;
+  }
+  virtual void Invalidate(const LayoutDeviceIntRect& aRect) override {
+    // TODO: see if we need to do anything here.
+  }
+  virtual nsresult SetTitle(const nsAString& title) override {
+    // Headless widgets have no title, so just ignore it.
+    return NS_OK;
+  }
+  virtual nsresult SetNonClientMargins(
+      LayoutDeviceIntMargin& margins) override {
+    // Headless widgets have no chrome margins, so just ignore the call.
+    return NS_OK;
+  }
+  virtual LayoutDeviceIntPoint WidgetToScreenOffset() override;
+  virtual void SetInputContext(const InputContext& aContext,
+                               const InputContextAction& aAction) override {
+    mInputContext = aContext;
+  }
+  virtual InputContext GetInputContext() override { return mInputContext; }
+
+  virtual LayerManager* GetLayerManager(
+      PLayerTransactionChild* aShadowManager = nullptr,
+      LayersBackend aBackendHint = mozilla::layers::LayersBackend::LAYERS_NONE,
+      LayerManagerPersistence aPersistence = LAYER_MANAGER_CURRENT) override;
+
+  void SetCompositorWidgetDelegate(CompositorWidgetDelegate* delegate) override;
+
+  [[nodiscard]] virtual nsresult AttachNativeKeyEvent(
+      WidgetKeyboardEvent& aEvent) override;
+  virtual bool GetEditCommands(NativeKeyBindingsType aType,
+                               const WidgetKeyboardEvent& aEvent,
+                               nsTArray<CommandInt>& aCommands) override;
+
+  virtual nsresult DispatchEvent(WidgetGUIEvent* aEvent,
+                                 nsEventStatus& aStatus) override;
+
+  virtual nsresult SynthesizeNativeMouseEvent(LayoutDeviceIntPoint aPoint,
+                                              uint32_t aNativeMessage,
+                                              uint32_t aModifierFlags,
+                                              nsIObserver* aObserver) override;
+  virtual nsresult SynthesizeNativeMouseMove(LayoutDeviceIntPoint aPoint,
+                                             nsIObserver* aObserver) override {
+    return SynthesizeNativeMouseEvent(aPoint, MOZ_HEADLESS_MOUSE_MOVE, 0,
+                                      aObserver);
+  };
+
+  virtual nsresult SynthesizeNativeMouseScrollEvent(
+      LayoutDeviceIntPoint aPoint, uint32_t aNativeMessage, double aDeltaX,
+      double aDeltaY, double aDeltaZ, uint32_t aModifierFlags,
+      uint32_t aAdditionalFlags, nsIObserver* aObserver) override;
+
+  virtual nsresult SynthesizeNativeTouchPoint(uint32_t aPointerId,
+                                              TouchPointerState aPointerState,
+                                              LayoutDeviceIntPoint aPoint,
+                                              double aPointerPressure,
+                                              uint32_t aPointerOrientation,
+                                              nsIObserver* aObserver) override;
+
+ private:
+  ~HeadlessWidget();
+  bool mEnabled;
+  bool mVisible;
+  bool mDestroyed;
+  nsIWidget* mTopLevel;
+  HeadlessCompositorWidget* mCompositorWidget;
+  // The size mode before entering fullscreen mode.
+  nsSizeMode mLastSizeMode;
+  // The last size mode set while the window was visible.
+  nsSizeMode mEffectiveSizeMode;
+  InputContext mInputContext;
+  mozilla::UniquePtr<mozilla::MultiTouchInput> mSynthesizedTouchInput;
+  // In headless there is no window manager to track window bounds
+  // across size mode changes, so we must track it to emulate.
+  LayoutDeviceIntRect mRestoreBounds;
+  void ApplySizeModeSideEffects();
+  // Similarly, we must track the active window ourselves in order
+  // to dispatch (de)activation events properly.
+  void RaiseWindow();
+  // The top level widgets are tracked for window ordering. They are
+  // stored in order of activation where the last element is always the
+  // currently active widget.
+  static StaticAutoPtr<nsTArray<HeadlessWidget*>> sActiveWindows;
+  // Get the most recently activated widget or null if there are none.
+  static already_AddRefed<HeadlessWidget> GetActiveWindow();
+};
+
+}  // namespace widget
+}  // namespace mozilla
+
+#endif
diff --git a/widget/headless/HeadlessWidgetTypes.ipdlh b/widget/headless/HeadlessWidgetTypes.ipdlh
new file mode 100644
index 0000000000..3dba0a2ddd
--- /dev/null
+++ b/widget/headless/HeadlessWidgetTypes.ipdlh
@@ -0,0 +1,18 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=99: */
+/* 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/. */
+
+using mozilla::LayoutDeviceIntSize from "Units.h";
+
+namespace mozilla {
+namespace widget {
+
+struct HeadlessCompositorWidgetInitData
+{
+  LayoutDeviceIntSize InitialClientSize;
+};
+
+} // namespace widget
+} // namespace mozilla
diff --git a/widget/headless/moz.build b/widget/headless/moz.build
new file mode 100644
index 0000000000..ea9a69c11b
--- /dev/null
+++ b/widget/headless/moz.build
@@ -0,0 +1,49 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+with Files("**"):
+    BUG_COMPONENT = ("Firefox", "Headless")
+
+DIRS += ["tests"]
+
+LOCAL_INCLUDES += [
+    "/widget",
+    "/widget/headless",
+]
+
+widget_dir = CONFIG["MOZ_WIDGET_TOOLKIT"]
+
+LOCAL_INCLUDES += [
+    "/widget/%s" % widget_dir,
+]
+
+UNIFIED_SOURCES += [
+    "HeadlessClipboard.cpp",
+    "HeadlessClipboardData.cpp",
+    "HeadlessCompositorWidget.cpp",
+    "HeadlessScreenHelper.cpp",
+    "HeadlessSound.cpp",
+    "HeadlessWidget.cpp",
+]
+
+if widget_dir == "gtk":
+    UNIFIED_SOURCES += [
+        "HeadlessLookAndFeelGTK.cpp",
+        "HeadlessThemeGTK.cpp",
+    ]
+
+if CONFIG["MOZ_WIDGET_TOOLKIT"] == "cocoa":
+    UNIFIED_SOURCES += [
+        "HeadlessKeyBindingsCocoa.mm",
+    ]
+else:
+    UNIFIED_SOURCES += [
+        "HeadlessKeyBindings.cpp",
+    ]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+FINAL_LIBRARY = "xul"
diff --git a/widget/headless/tests/.eslintrc.js b/widget/headless/tests/.eslintrc.js
new file mode 100644
index 0000000000..69e89d0054
--- /dev/null
+++ b/widget/headless/tests/.eslintrc.js
@@ -0,0 +1,5 @@
+"use strict";
+
+module.exports = {
+  extends: ["plugin:mozilla/xpcshell-test"],
+};
diff --git a/widget/headless/tests/headless.html b/widget/headless/tests/headless.html
new file mode 100644
index 0000000000..bbde895077
--- /dev/null
+++ b/widget/headless/tests/headless.html
@@ -0,0 +1,6 @@
+<html>
+<head><meta content="text/html; charset=utf-8" http-equiv="Content-Type"></head>
+<body style="background-color: rgb(0, 255, 0); color: rgb(0, 0, 255)">
+Hi
+</body>
+</html>
diff --git a/widget/headless/tests/headless_button.html b/widget/headless/tests/headless_button.html
new file mode 100644
index 0000000000..5641066bfe
--- /dev/null
+++ b/widget/headless/tests/headless_button.html
@@ -0,0 +1,6 @@
+<html>
+<head><meta content="text/html; charset=utf-8" http-equiv="Content-Type"></head>
+<body>
+<button id="btn">button</button>
+</body>
+</html>
diff --git a/widget/headless/tests/moz.build b/widget/headless/tests/moz.build
new file mode 100644
index 0000000000..e48fa734e0
--- /dev/null
+++ b/widget/headless/tests/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/.
+
+XPCSHELL_TESTS_MANIFESTS += ["xpcshell.ini"]
diff --git a/widget/headless/tests/test_headless.js b/widget/headless/tests/test_headless.js
new file mode 100644
index 0000000000..79486a9d8c
--- /dev/null
+++ b/widget/headless/tests/test_headless.js
@@ -0,0 +1,215 @@
+/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set sts=2 sw=2 et tw=80: */
+"use strict";
+const { Services } = ChromeUtils.import("resource://gre/modules/Services.jsm");
+const { HttpServer } = ChromeUtils.import("resource://testing-common/httpd.js");
+
+const gProfDir = do_get_profile();
+const server = new HttpServer();
+server.registerDirectory("/", do_get_cwd());
+server.start(-1);
+const ROOT = `http://localhost:${server.identity.primaryPort}`;
+const BASE = `${ROOT}/`;
+const HEADLESS_URL = `${BASE}/headless.html`;
+const HEADLESS_BUTTON_URL = `${BASE}/headless_button.html`;
+registerCleanupFunction(() => {
+  server.stop(() => {});
+});
+
+// Refrences to the progress listeners to keep them from being gc'ed
+// before they are called.
+const progressListeners = new Map();
+
+function loadContentWindow(windowlessBrowser, uri) {
+  return new Promise((resolve, reject) => {
+    let loadURIOptions = {
+      triggeringPrincipal: Services.scriptSecurityManager.getSystemPrincipal(),
+    };
+    windowlessBrowser.loadURI(uri, loadURIOptions);
+    let docShell = windowlessBrowser.docShell;
+    let webProgress = docShell
+      .QueryInterface(Ci.nsIInterfaceRequestor)
+      .getInterface(Ci.nsIWebProgress);
+    let progressListener = {
+      onLocationChange(progress, request, location, flags) {
+        // Ignore inner-frame events
+        if (progress != webProgress) {
+          return;
+        }
+        // Ignore events that don't change the document
+        if (flags & Ci.nsIWebProgressListener.LOCATION_CHANGE_SAME_DOCUMENT) {
+          return;
+        }
+        let contentWindow = docShell.domWindow;
+        webProgress.removeProgressListener(progressListener);
+        progressListeners.delete(progressListener);
+        contentWindow.addEventListener(
+          "load",
+          event => {
+            resolve(contentWindow);
+          },
+          { once: true }
+        );
+      },
+      QueryInterface: ChromeUtils.generateQI([
+        "nsIWebProgressListener",
+        "nsISupportsWeakReference",
+      ]),
+    };
+    progressListeners.set(progressListener, progressListener);
+    webProgress.addProgressListener(
+      progressListener,
+      Ci.nsIWebProgress.NOTIFY_LOCATION
+    );
+  });
+}
+
+add_task(async function test_snapshot() {
+  let windowlessBrowser = Services.appShell.createWindowlessBrowser(false);
+  let contentWindow = await loadContentWindow(windowlessBrowser, HEADLESS_URL);
+  const contentWidth = 400;
+  const contentHeight = 300;
+  // Verify dimensions.
+  contentWindow.resizeTo(contentWidth, contentHeight);
+  equal(contentWindow.innerWidth, contentWidth);
+  equal(contentWindow.innerHeight, contentHeight);
+
+  // Snapshot the test page.
+  let canvas = contentWindow.document.createElementNS(
+    "http://www.w3.org/1999/xhtml",
+    "html:canvas"
+  );
+  let context = canvas.getContext("2d");
+  let width = contentWindow.innerWidth;
+  let height = contentWindow.innerHeight;
+  canvas.width = width;
+  canvas.height = height;
+  context.drawWindow(contentWindow, 0, 0, width, height, "rgb(255, 255, 255)");
+  let imageData = context.getImageData(0, 0, width, height).data;
+  ok(
+    imageData[0] === 0 &&
+      imageData[1] === 255 &&
+      imageData[2] === 0 &&
+      imageData[3] === 255,
+    "Page is green."
+  );
+
+  // Search for a blue pixel (a quick and dirty check to see if the blue text is
+  // on the page)
+  let found = false;
+  for (let i = 0; i < imageData.length; i += 4) {
+    if (imageData[i + 2] === 255) {
+      found = true;
+      break;
+    }
+  }
+  ok(found, "Found blue text on page.");
+
+  windowlessBrowser.close();
+});
+
+add_task(async function test_snapshot_widget_layers() {
+  let windowlessBrowser = Services.appShell.createWindowlessBrowser(false);
+  // nsIWindowlessBrowser inherits from nsIWebNavigation.
+  let contentWindow = await loadContentWindow(windowlessBrowser, HEADLESS_URL);
+  const contentWidth = 1;
+  const contentHeight = 2;
+  // Verify dimensions.
+  contentWindow.resizeTo(contentWidth, contentHeight);
+  equal(contentWindow.innerWidth, contentWidth);
+  equal(contentWindow.innerHeight, contentHeight);
+
+  // Snapshot the test page.
+  let canvas = contentWindow.document.createElementNS(
+    "http://www.w3.org/1999/xhtml",
+    "html:canvas"
+  );
+  let context = canvas.getContext("2d");
+  let width = contentWindow.innerWidth;
+  let height = contentWindow.innerHeight;
+  canvas.width = width;
+  canvas.height = height;
+  context.drawWindow(
+    contentWindow,
+    0,
+    0,
+    width,
+    height,
+    "rgb(255, 255, 255)",
+    context.DRAWWINDOW_DRAW_CARET |
+      context.DRAWWINDOW_DRAW_VIEW |
+      context.DRAWWINDOW_USE_WIDGET_LAYERS
+  );
+  ok(true, "Snapshot with widget layers didn't crash.");
+
+  windowlessBrowser.close();
+});
+
+// Ensure keydown events are triggered on the windowless browser.
+add_task(async function test_keydown() {
+  let windowlessBrowser = Services.appShell.createWindowlessBrowser(false);
+  // nsIWindowlessBrowser inherits from nsIWebNavigation.
+  let contentWindow = await loadContentWindow(windowlessBrowser, HEADLESS_URL);
+
+  let keydown = new Promise(resolve => {
+    contentWindow.addEventListener(
+      "keydown",
+      () => {
+        resolve();
+      },
+      { once: true }
+    );
+  });
+
+  let tip = Cc["@mozilla.org/text-input-processor;1"].createInstance(
+    Ci.nsITextInputProcessor
+  );
+  let begun = tip.beginInputTransactionForTests(contentWindow);
+  ok(
+    begun,
+    "nsITextInputProcessor.beginInputTransactionForTests() should succeed"
+  );
+  tip.keydown(
+    new contentWindow.KeyboardEvent("", {
+      key: "a",
+      code: "KeyA",
+      keyCode: contentWindow.KeyboardEvent.DOM_VK_A,
+    })
+  );
+
+  await keydown;
+  ok(true, "Send keydown didn't crash");
+
+  windowlessBrowser.close();
+});
+
+// Test dragging the mouse on a button to ensure the creation of the drag
+// service doesn't crash in headless.
+add_task(async function test_mouse_drag() {
+  let windowlessBrowser = Services.appShell.createWindowlessBrowser(false);
+  // nsIWindowlessBrowser inherits from nsIWebNavigation.
+  let contentWindow = await loadContentWindow(
+    windowlessBrowser,
+    HEADLESS_BUTTON_URL
+  );
+  contentWindow.resizeTo(400, 400);
+
+  let target = contentWindow.document.getElementById("btn");
+  let rect = target.getBoundingClientRect();
+  let left = rect.left;
+  let top = rect.top;
+
+  let utils = contentWindow.windowUtils;
+  utils.sendMouseEvent("mousedown", left, top, 0, 1, 0, false, 0, 0);
+  utils.sendMouseEvent("mousemove", left, top, 0, 1, 0, false, 0, 0);
+  // Wait for a turn of the event loop since the synthetic mouse event
+  // that creates the drag service is processed during the refresh driver.
+  await new Promise(r => {
+    executeSoon(r);
+  });
+  utils.sendMouseEvent("mouseup", left, top, 0, 1, 0, false, 0, 0);
+
+  ok(true, "Send mouse event didn't crash");
+
+  windowlessBrowser.close();
+});
diff --git a/widget/headless/tests/test_headless_clipboard.js b/widget/headless/tests/test_headless_clipboard.js
new file mode 100644
index 0000000000..6c0ffcd5a1
--- /dev/null
+++ b/widget/headless/tests/test_headless_clipboard.js
@@ -0,0 +1,46 @@
+/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set sts=2 sw=2 et tw=80: */
+"use strict";
+const { Services } = ChromeUtils.import("resource://gre/modules/Services.jsm");
+
+function getString(clipboard) {
+  var str = "";
+
+  // Create transferable that will transfer the text.
+  var trans = Cc["@mozilla.org/widget/transferable;1"].createInstance(
+    Ci.nsITransferable
+  );
+  trans.init(null);
+  trans.addDataFlavor("text/unicode");
+
+  clipboard.getData(trans, Ci.nsIClipboard.kGlobalClipboard);
+
+  try {
+    var data = {};
+    trans.getTransferData("text/unicode", data);
+
+    if (data) {
+      data = data.value.QueryInterface(Ci.nsISupportsString);
+      str = data.data;
+    }
+  } catch (ex) {
+    // If the clipboard is empty getTransferData will throw.
+  }
+
+  return str;
+}
+
+add_task(async function test_clipboard() {
+  let clipboard = Services.clipboard;
+
+  // Test copy.
+  const data = "random number: " + Math.random();
+  let helper = Cc["@mozilla.org/widget/clipboardhelper;1"].getService(
+    Ci.nsIClipboardHelper
+  );
+  helper.copyString(data);
+  equal(getString(clipboard), data, "Data was successfully copied.");
+
+  clipboard.emptyClipboard(Ci.nsIClipboard.kGlobalClipboard);
+  equal(getString(clipboard), "", "Data was successfully cleared.");
+});
diff --git a/widget/headless/tests/xpcshell.ini b/widget/headless/tests/xpcshell.ini
new file mode 100644
index 0000000000..307a12cb0d
--- /dev/null
+++ b/widget/headless/tests/xpcshell.ini
@@ -0,0 +1,10 @@
+[DEFAULT]
+skip-if = toolkit != "gtk" && toolkit != "windows"
+headless = true
+
+[test_headless_clipboard.js]
+[test_headless.js]
+skip-if = appname == "thunderbird"
+support-files =
+  headless.html
+  headless_button.html