diff --git a/gfx/layers/apz/test/mochitest/test_group_scroll_snap.html b/gfx/layers/apz/test/mochitest/test_group_scroll_snap.html
index ea288ebf7e47..9a1341c503ef 100644
--- a/gfx/layers/apz/test/mochitest/test_group_scroll_snap.html
+++ b/gfx/layers/apz/test/mochitest/test_group_scroll_snap.html
@@ -44,6 +44,8 @@ const subtests = [
    "prefs": [["layout.css.scroll-behavior.spring-constant", 1000],
              // Avoid fling at the end of pan.
              ["apz.fling_min_velocity_threshold", "10000"],
+             // This test needs mSimilateMomentum flag on headless mode.
+             ["apz.test.headless.simulate_momentum", true],
              ["apz.gtk.kinetic_scroll.enabled", true],
              // Use the pixel mode to make the test predictable easily.
              ["apz.gtk.kinetic_scroll.delta_mode", 2],
diff --git a/widget/headless/HeadlessWidget.cpp b/widget/headless/HeadlessWidget.cpp
index c1fbcccc93d9..340cb723bd4d 100644
--- a/widget/headless/HeadlessWidget.cpp
+++ b/widget/headless/HeadlessWidget.cpp
@@ -12,6 +12,7 @@
 #include "mozilla/ClearOnShutdown.h"
 #include "mozilla/Maybe.h"
 #include "mozilla/NativeKeyBindingsType.h"
+#include "mozilla/Preferences.h"
 #include "mozilla/TextEventDispatcher.h"
 #include "mozilla/TextEvents.h"
 #include "mozilla/WritingModes.h"
@@ -545,13 +546,14 @@ nsresult HeadlessWidget::SynthesizeNativeTouchPadPinch(
       return NS_ERROR_INVALID_ARG;
   }
 
-  LayoutDeviceIntPoint touchpadPoint = aPoint - WidgetToScreenOffset();
+  ScreenPoint touchpadPoint = ViewAs<ScreenPixel>(
+      aPoint - WidgetToScreenOffset(),
+      PixelCastJustification::LayoutDeviceIsScreenForUntransformedEvent);
   // The headless widget does not support modifiers.
   // Do not pass `aModifierFlags` because it contains native modifier values.
   PinchGestureInput inputToDispatch(
       pinchGestureType, PinchGestureInput::TRACKPAD, PR_IntervalNow(),
-      TimeStamp::Now(), ExternalPoint(0, 0),
-      ScreenPoint(touchpadPoint.x, touchpadPoint.y),
+      TimeStamp::Now(), ExternalPoint(0, 0), touchpadPoint,
       100.0 * ((aEventPhase == PHASE_END) ? ScreenCoord(1.f) : CurrentSpan),
       100.0 * ((aEventPhase == PHASE_END) ? ScreenCoord(1.f) : PreviousSpan),
       0);
@@ -564,5 +566,47 @@ nsresult HeadlessWidget::SynthesizeNativeTouchPadPinch(
   DispatchPinchGestureInput(inputToDispatch);
   return NS_OK;
 }
+
+nsresult HeadlessWidget::SynthesizeNativeTouchpadPan(
+    TouchpadGesturePhase aEventPhase, LayoutDeviceIntPoint aPoint,
+    double aDeltaX, double aDeltaY, int32_t aModifierFlags,
+    nsIObserver* aObserver) {
+  AutoObserverNotifier notifier(aObserver, "touchpadpanevent");
+
+  MOZ_ASSERT(NS_IsMainThread());
+
+  PanGestureInput::PanGestureType eventType = PanGestureInput::PANGESTURE_PAN;
+  switch (aEventPhase) {
+    case PHASE_BEGIN:
+      eventType = PanGestureInput::PANGESTURE_START;
+      break;
+    case PHASE_UPDATE:
+      eventType = PanGestureInput::PANGESTURE_PAN;
+      break;
+    case PHASE_END:
+      eventType = PanGestureInput::PANGESTURE_END;
+      break;
+    default:
+      return NS_ERROR_INVALID_ARG;
+  }
+
+  ScreenPoint touchpadPoint = ViewAs<ScreenPixel>(
+      aPoint - WidgetToScreenOffset(),
+      PixelCastJustification::LayoutDeviceIsScreenForUntransformedEvent);
+  PanGestureInput input(eventType, PR_IntervalNow(), TimeStamp::Now(),
+                        touchpadPoint,
+                        ScreenPoint(float(aDeltaX), float(aDeltaY)),
+                        // Same as SynthesizeNativeTouchPadPinch case we ignore
+                        // aModifierFlags.
+                        0);
+
+  input.mSimulateMomentum =
+      Preferences::GetBool("apz.test.headless.simulate_momentum");
+
+  DispatchPanGestureInput(input);
+
+  return NS_OK;
+}
+
 }  // namespace widget
 }  // namespace mozilla
diff --git a/widget/headless/HeadlessWidget.h b/widget/headless/HeadlessWidget.h
index 2b80eea70e58..b77ec632a90f 100644
--- a/widget/headless/HeadlessWidget.h
+++ b/widget/headless/HeadlessWidget.h
@@ -135,6 +135,12 @@ class HeadlessWidget : public nsBaseWidget {
       TouchpadGesturePhase aEventPhase, float aScale,
       LayoutDeviceIntPoint aPoint, int32_t aModifierFlags) override;
 
+  virtual nsresult SynthesizeNativeTouchpadPan(TouchpadGesturePhase aEventPhase,
+                                               LayoutDeviceIntPoint aPoint,
+                                               double aDeltaX, double aDeltaY,
+                                               int32_t aModifierFlags,
+                                               nsIObserver* aObserver) override;
+
  private:
   ~HeadlessWidget();
   bool mEnabled;