diff --git a/widget/cocoa/nsChildView.mm b/widget/cocoa/nsChildView.mm
index 823d92c19624..4789d738f212 100644
--- a/widget/cocoa/nsChildView.mm
+++ b/widget/cocoa/nsChildView.mm
@@ -1919,36 +1919,8 @@ void nsChildView::DispatchAPZWheelInputEvent(InputData& aEvent, bool aCanTrigger
           return;
         }
 
-        PanGestureInput& panInput = aEvent.AsPanGestureInput();
-
-        event = panInput.ToWidgetEvent(this);
-        if (aCanTriggerSwipe && panInput.mOverscrollBehaviorAllowsSwipe) {
-          SwipeInfo swipeInfo = SendMayStartSwipe(panInput);
-          event.mCanTriggerSwipe = swipeInfo.wantsSwipe;
-          if (swipeInfo.wantsSwipe) {
-            if (result.GetStatus() == nsEventStatus_eIgnore) {
-              // APZ has determined and that scrolling horizontally in the
-              // requested direction is impossible, so it didn't do any
-              // scrolling for the event.
-              // We know now that MayStartSwipe wants a swipe, so we can start
-              // the swipe now.
-              TrackScrollEventAsSwipe(panInput, swipeInfo.allowedDirections);
-            } else {
-              // We don't know whether this event can start a swipe, so we need
-              // to queue up events and wait for a call to ReportSwipeStarted.
-              // APZ might already have started scrolling in response to the
-              // event if it knew that it's the right thing to do. In that case
-              // we'll still get a call to ReportSwipeStarted, and we will
-              // discard the queued events at that point.
-              mSwipeEventQueue =
-                  MakeUnique<SwipeEventQueue>(swipeInfo.allowedDirections, result.mInputBlockId);
-            }
-          }
-        }
-
-        if (mSwipeEventQueue && mSwipeEventQueue->inputBlockId == result.mInputBlockId) {
-          mSwipeEventQueue->queuedEvents.AppendElement(panInput);
-        }
+        event = MayStartSwipeForAPZ(aEvent.AsPanGestureInput(), result,
+                                    CanTriggerSwipe{aCanTriggerSwipe});
         break;
       }
       case SCROLLWHEEL_INPUT: {
@@ -1977,48 +1949,10 @@ void nsChildView::DispatchAPZWheelInputEvent(InputData& aEvent, bool aCanTrigger
   nsEventStatus status;
   switch (aEvent.mInputType) {
     case PANGESTURE_INPUT: {
-      PanGestureInput panInput = aEvent.AsPanGestureInput();
-      if (panInput.mType == PanGestureInput::PANGESTURE_MAYSTART ||
-          panInput.mType == PanGestureInput::PANGESTURE_START) {
-        mCurrentPanGestureBelongsToSwipe = false;
-      }
-      if (mCurrentPanGestureBelongsToSwipe) {
-        // Ignore this event. It's a momentum event from a scroll gesture
-        // that was processed as a swipe, and the swipe animation has
-        // already finished (so mSwipeTracker is already null).
-        MOZ_ASSERT(panInput.IsMomentum(),
-                   "If the fingers are still on the touchpad, we should still have a SwipeTracker, "
-                   "and it should have consumed this event.");
-        return;
-      }
-
-      event = panInput.ToWidgetEvent(this);
-      if (aCanTriggerSwipe) {
-        SwipeInfo swipeInfo = SendMayStartSwipe(panInput);
-
-        // We're in the non-APZ case here, but we still want to know whether
-        // the event was routed to a child process, so we use InputAPZContext
-        // to get that piece of information.
-        ScrollableLayerGuid guid;
-        InputAPZContext context(guid, 0, nsEventStatus_eIgnore);
-
-        event.mCanTriggerSwipe = swipeInfo.wantsSwipe;
-        DispatchEvent(&event, status);
-        if (swipeInfo.wantsSwipe) {
-          if (context.WasRoutedToChildProcess()) {
-            // We don't know whether this event can start a swipe, so we need
-            // to queue up events and wait for a call to ReportSwipeStarted.
-            mSwipeEventQueue = MakeUnique<SwipeEventQueue>(swipeInfo.allowedDirections, 0);
-          } else if (event.TriggersSwipe()) {
-            TrackScrollEventAsSwipe(panInput, swipeInfo.allowedDirections);
-          }
-        }
-
-        if (mSwipeEventQueue && mSwipeEventQueue->inputBlockId == 0) {
-          mSwipeEventQueue->queuedEvents.AppendElement(panInput);
-        }
+      if (MayStartSwipeForNonAPZ(aEvent.AsPanGestureInput(), CanTriggerSwipe{aCanTriggerSwipe})) {
         return;
       }
+      event = aEvent.AsPanGestureInput().ToWidgetEvent(this);
       break;
     }
     case SCROLLWHEEL_INPUT: {
diff --git a/widget/nsBaseWidget.cpp b/widget/nsBaseWidget.cpp
index 51d367d32a18..5bffe19b0c9d 100644
--- a/widget/nsBaseWidget.cpp
+++ b/widget/nsBaseWidget.cpp
@@ -2114,6 +2114,94 @@ nsBaseWidget::SwipeInfo nsBaseWidget::SendMayStartSwipe(
   return result;
 }
 
+WidgetWheelEvent nsBaseWidget::MayStartSwipeForAPZ(
+    const PanGestureInput& aPanInput, const APZEventResult& aApzResult,
+    CanTriggerSwipe aCanTriggerSwipe) {
+  WidgetWheelEvent event = aPanInput.ToWidgetEvent(this);
+  if (aCanTriggerSwipe == CanTriggerSwipe::Yes &&
+      aPanInput.mOverscrollBehaviorAllowsSwipe) {
+    SwipeInfo swipeInfo = SendMayStartSwipe(aPanInput);
+    event.mCanTriggerSwipe = swipeInfo.wantsSwipe;
+    if (swipeInfo.wantsSwipe) {
+      if (aApzResult.GetStatus() == nsEventStatus_eIgnore) {
+        // APZ has determined and that scrolling horizontally in the
+        // requested direction is impossible, so it didn't do any
+        // scrolling for the event.
+        // We know now that MayStartSwipe wants a swipe, so we can start
+        // the swipe now.
+        TrackScrollEventAsSwipe(aPanInput, swipeInfo.allowedDirections);
+      } else {
+        // We don't know whether this event can start a swipe, so we need
+        // to queue up events and wait for a call to ReportSwipeStarted.
+        // APZ might already have started scrolling in response to the
+        // event if it knew that it's the right thing to do. In that case
+        // we'll still get a call to ReportSwipeStarted, and we will
+        // discard the queued events at that point.
+        mSwipeEventQueue = MakeUnique<SwipeEventQueue>(
+            swipeInfo.allowedDirections, aApzResult.mInputBlockId);
+      }
+    }
+  }
+
+  if (mSwipeEventQueue &&
+      mSwipeEventQueue->inputBlockId == aApzResult.mInputBlockId) {
+    mSwipeEventQueue->queuedEvents.AppendElement(aPanInput);
+  }
+
+  return event;
+}
+
+bool nsBaseWidget::MayStartSwipeForNonAPZ(const PanGestureInput& aPanInput,
+                                          CanTriggerSwipe aCanTriggerSwipe) {
+  if (aPanInput.mType == PanGestureInput::PANGESTURE_MAYSTART ||
+      aPanInput.mType == PanGestureInput::PANGESTURE_START) {
+    mCurrentPanGestureBelongsToSwipe = false;
+  }
+  if (mCurrentPanGestureBelongsToSwipe) {
+    // Ignore this event. It's a momentum event from a scroll gesture
+    // that was processed as a swipe, and the swipe animation has
+    // already finished (so mSwipeTracker is already null).
+    MOZ_ASSERT(aPanInput.IsMomentum(),
+               "If the fingers are still on the touchpad, we should still have "
+               "a SwipeTracker, "
+               "and it should have consumed this event.");
+    return true;
+  }
+
+  if (aCanTriggerSwipe == CanTriggerSwipe::No) {
+    return false;
+  }
+
+  SwipeInfo swipeInfo = SendMayStartSwipe(aPanInput);
+
+  // We're in the non-APZ case here, but we still want to know whether
+  // the event was routed to a child process, so we use InputAPZContext
+  // to get that piece of information.
+  ScrollableLayerGuid guid;
+  InputAPZContext context(guid, 0, nsEventStatus_eIgnore);
+
+  WidgetWheelEvent event = aPanInput.ToWidgetEvent(this);
+  event.mCanTriggerSwipe = swipeInfo.wantsSwipe;
+  nsEventStatus status;
+  DispatchEvent(&event, status);
+  if (swipeInfo.wantsSwipe) {
+    if (context.WasRoutedToChildProcess()) {
+      // We don't know whether this event can start a swipe, so we need
+      // to queue up events and wait for a call to ReportSwipeStarted.
+      mSwipeEventQueue =
+          MakeUnique<SwipeEventQueue>(swipeInfo.allowedDirections, 0);
+    } else if (event.TriggersSwipe()) {
+      TrackScrollEventAsSwipe(aPanInput, swipeInfo.allowedDirections);
+    }
+  }
+
+  if (mSwipeEventQueue && mSwipeEventQueue->inputBlockId == 0) {
+    mSwipeEventQueue->queuedEvents.AppendElement(aPanInput);
+  }
+
+  return true;
+}
+
 const IMENotificationRequests& nsIWidget::IMENotificationRequestsRef() {
   TextEventDispatcher* dispatcher = GetTextEventDispatcher();
   return dispatcher->IMENotificationRequestsRef();
diff --git a/widget/nsBaseWidget.h b/widget/nsBaseWidget.h
index 3985f6f9feb0..aea5a1602c9a 100644
--- a/widget/nsBaseWidget.h
+++ b/widget/nsBaseWidget.h
@@ -40,6 +40,7 @@ class LiveResizeListener;
 class FallbackRenderer;
 class SwipeTracker;
 struct SwipeEventQueue;
+class WidgetWheelEvent;
 
 #ifdef ACCESSIBILITY
 namespace a11y {
@@ -335,6 +336,21 @@ class nsBaseWidget : public nsIWidget, public nsSupportsWeakReference {
     uint32_t allowedDirections;
   };
   SwipeInfo SendMayStartSwipe(const mozilla::PanGestureInput& aSwipeStartEvent);
+  enum class CanTriggerSwipe : bool {
+    No = false,
+    Yes = true,
+  };
+  // Returns a WidgetWheelEvent which needs to be handled by APZ regardless of
+  // whether |aPanInput| event was used for SwipeTracker or not.
+  mozilla::WidgetWheelEvent MayStartSwipeForAPZ(
+      const mozilla::PanGestureInput& aPanInput,
+      const mozilla::layers::APZEventResult& aApzResult,
+      CanTriggerSwipe aCanTriggerSwipe);
+
+  // Returns true if |aPanInput| event was used for SwipeTracker, false
+  // otherwise.
+  bool MayStartSwipeForNonAPZ(const mozilla::PanGestureInput& aPanInput,
+                              CanTriggerSwipe aCanTriggerSwipe);
 
   void NotifyWindowDestroyed();
   void NotifySizeMoveDone();