diff --git a/dom/base/nsDOMWindowUtils.cpp b/dom/base/nsDOMWindowUtils.cpp
index 7fd9dad16f..638ab1135c 100644
--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -1030,9 +1030,7 @@ nsDOMWindowUtils::SendWheelEvent(float aX,
 
   wheelEvent.refPoint = ToWidgetPoint(CSSPoint(aX, aY), offset, presContext);
 
-  nsEventStatus status;
-  nsresult rv = widget->DispatchEvent(&wheelEvent, status);
-  NS_ENSURE_SUCCESS(rv, rv);
+  widget->DispatchAPZAwareEvent(&wheelEvent);
 
   bool failedX = false;
   if ((aOptions & WHEEL_EVENT_EXPECTED_OVERFLOW_DELTA_X_ZERO) &&
diff --git a/dom/events/EventStateManager.cpp b/dom/events/EventStateManager.cpp
index c178edc7aa..595c82c169 100644
--- a/dom/events/EventStateManager.cpp
+++ b/dom/events/EventStateManager.cpp
@@ -87,6 +87,7 @@
 #include "mozilla/LookAndFeel.h"
 #include "GoannaProfiler.h"
 #include "Units.h"
+#include "mozilla/layers/APZCTreeManager.h"
 
 #ifdef XP_MACOSX
 #import <ApplicationServices/ApplicationServices.h>
@@ -3046,13 +3047,18 @@ EventStateManager::PostHandleEvent(nsPresContext* aPresContext,
       }
 
       WidgetWheelEvent* wheelEvent = aEvent->AsWheelEvent();
-      switch (WheelPrefs::GetInstance()->ComputeActionFor(wheelEvent)) {
-        case WheelPrefs::ACTION_HSCROLL: {
-          // Swap axes and fall through
-          double deltaX = wheelEvent->deltaX;
-          wheelEvent->deltaX = wheelEvent->deltaY;
-          wheelEvent->deltaY = deltaX;
-        }
+
+      // When APZ is enabled, the actual scroll animation might be handled by
+      // the compositor.
+      WheelPrefs::Action action;
+      if (gfxPrefs::AsyncPanZoomEnabled() &&
+          layers::APZCTreeManager::WillHandleWheelEvent(wheelEvent))
+      {
+        action = WheelPrefs::ACTION_NONE;
+      } else {
+        action = WheelPrefs::GetInstance()->ComputeActionFor(wheelEvent);
+      }
+      switch (action) {
         case WheelPrefs::ACTION_SCROLL: {
           // For scrolling of default action, we should honor the mouse wheel
           // transaction.
diff --git a/dom/events/EventStateManager.h b/dom/events/EventStateManager.h
index fe94041f44..3abc247a33 100644
--- a/dom/events/EventStateManager.h
+++ b/dom/events/EventStateManager.h
@@ -447,8 +447,7 @@ protected:
       ACTION_SCROLL,
       ACTION_HISTORY,
       ACTION_ZOOM,
-      ACTION_HSCROLL,
-      ACTION_LAST = ACTION_HSCROLL
+      ACTION_LAST = ACTION_ZOOM
     };
     Action ComputeActionFor(WidgetWheelEvent* aEvent);
 
diff --git a/dom/events/test/mochitest.ini b/dom/events/test/mochitest.ini
index c31a5183e9..66142ed386 100644
--- a/dom/events/test/mochitest.ini
+++ b/dom/events/test/mochitest.ini
@@ -131,6 +131,7 @@ skip-if = buildapp == 'mulet' || buildapp == 'b2g' # b2g(failing when the test g
 [test_bug944011.html]
 [test_bug944847.html]
 [test_bug946632.html]
+skip-if = buildapp == 'b2g'
 [test_bug967796.html]
 skip-if = toolkit == "gonk" || e10s
 [test_bug985988.html]
@@ -165,7 +166,7 @@ skip-if = toolkit == 'android' #CRASH_DUMP, RANDOM
 skip-if = buildapp == 'mulet'
 [test_messageEvent.html]
 [test_moz_mouse_pixel_scroll_event.html]
-skip-if = buildapp == 'mulet'
+skip-if = buildapp == 'mulet' || buildapp == 'b2g' # bug 1126090, no wheel events on b2g
 [test_onerror_handler_args.html]
 [test_wheel_default_action.html]
 skip-if = buildapp == 'mulet' || buildapp == 'b2g' || e10s
diff --git a/dom/events/test/test_bug946632.html b/dom/events/test/test_bug946632.html
index 2de34ed951..7e2154d34c 100644
--- a/dom/events/test/test_bug946632.html
+++ b/dom/events/test/test_bug946632.html
@@ -7,6 +7,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=946632
   <title>Test for bug 946632 - propagate mouse-wheel vertical scroll events to container</title>
   <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
   <script type="application/javascript" src="/tests/SimpleTest/EventUtils.js"></script>
+  <script type="application/javascript" src="/tests/SimpleTest/paint_listener.js"></script>
   <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
   <style>
     .scrollable {
@@ -125,7 +126,10 @@ function nextTest()
   var test = tests[i];
   ++i;
   prepare(test.check);
-  test.test();
+
+  window.waitForAllPaintsFlushed(function() {
+    test.test();
+  });
 }
 
 function runTests()
diff --git a/dom/ipc/PBrowser.ipdl b/dom/ipc/PBrowser.ipdl
index 4ef09aee9f..cd1642edef 100644
--- a/dom/ipc/PBrowser.ipdl
+++ b/dom/ipc/PBrowser.ipdl
@@ -484,6 +484,8 @@ parent:
      */
     async SetDimensions(uint32_t aFlags, int32_t aX, int32_t aY, int32_t aCx, int32_t aCy);
 
+    prio(high) sync SynthesizedMouseWheelEvent(WidgetWheelEvent event);
+
 child:
     /**
      * Notify the remote browser that it has been Show()n on this
diff --git a/dom/ipc/TabParent.cpp b/dom/ipc/TabParent.cpp
index a5aa259fe5..42272621e1 100644
--- a/dom/ipc/TabParent.cpp
+++ b/dom/ipc/TabParent.cpp
@@ -1235,6 +1235,21 @@ bool TabParent::SendMouseWheelEvent(WidgetWheelEvent& event)
   return PBrowserParent::SendMouseWheelEvent(event, guid, blockId);
 }
 
+bool TabParent::RecvSynthesizedMouseWheelEvent(const mozilla::WidgetWheelEvent& aEvent)
+{
+  nsCOMPtr<nsIWidget> widget = GetWidget();
+  if (!widget) {
+    return true;
+  }
+
+  WidgetWheelEvent localEvent(aEvent);
+  localEvent.widget = widget;
+  localEvent.refPoint -= GetChildProcessOffset();
+
+  widget->DispatchAPZAwareEvent(&localEvent);
+  return true;
+}
+
 static void
 DoCommandCallback(mozilla::Command aCommand, void* aData)
 {
diff --git a/dom/ipc/TabParent.h b/dom/ipc/TabParent.h
index c2c592fafc..b6743b8bfe 100644
--- a/dom/ipc/TabParent.h
+++ b/dom/ipc/TabParent.h
@@ -233,6 +233,7 @@ public:
                                                const bool& aPreventDefault) override;
     virtual bool RecvSetTargetAPZC(const uint64_t& aInputBlockId,
                                    nsTArray<ScrollableLayerGuid>&& aTargets) override;
+    virtual bool RecvSynthesizedMouseWheelEvent(const mozilla::WidgetWheelEvent& aEvent) override;
 
     virtual PColorPickerParent*
     AllocPColorPickerParent(const nsString& aTitle, const nsString& aInitialColor) override;
diff --git a/gfx/layers/apz/src/APZCTreeManager.cpp b/gfx/layers/apz/src/APZCTreeManager.cpp
index 3f6c9657d0..ad4fc2346d 100644
--- a/gfx/layers/apz/src/APZCTreeManager.cpp
+++ b/gfx/layers/apz/src/APZCTreeManager.cpp
@@ -854,6 +854,13 @@ APZCTreeManager::ProcessWheelEvent(WidgetWheelEvent& aEvent,
   return status;
 }
 
+bool
+APZCTreeManager::WillHandleWheelEvent(WidgetWheelEvent* aEvent)
+{
+  return EventStateManager::WheelEventIsScrollAction(aEvent) &&
+         aEvent->deltaMode == nsIDOMWheelEvent::DOM_DELTA_LINE;
+}
+
 nsEventStatus
 APZCTreeManager::ReceiveInputEvent(WidgetInputEvent& aEvent,
                                    ScrollableLayerGuid* aOutTargetGuid,
@@ -891,9 +898,7 @@ APZCTreeManager::ReceiveInputEvent(WidgetInputEvent& aEvent,
     }
     case eWheelEventClass: {
       WidgetWheelEvent& wheelEvent = *aEvent.AsWheelEvent();
-      if (wheelEvent.deltaMode != nsIDOMWheelEvent::DOM_DELTA_LINE ||
-          !EventStateManager::WheelEventIsScrollAction(&wheelEvent))
-      {
+      if (!WillHandleWheelEvent(&wheelEvent)) {
         // Don't send through APZ if we're not scrolling or if the delta mode
         // is not line-based.
         return ProcessEvent(aEvent, aOutTargetGuid, aOutInputBlockId);
diff --git a/gfx/layers/apz/src/APZCTreeManager.h b/gfx/layers/apz/src/APZCTreeManager.h
index 4dcb17824f..04a9abe069 100644
--- a/gfx/layers/apz/src/APZCTreeManager.h
+++ b/gfx/layers/apz/src/APZCTreeManager.h
@@ -382,6 +382,15 @@ public:
    */
   nsRefPtr<const OverscrollHandoffChain> BuildOverscrollHandoffChain(const nsRefPtr<AsyncPanZoomController>& aInitialTarget);
 
+public:
+  // Returns whether or not a wheel event action will be (or was) performed by
+  // APZ. If this returns true, the event must not perform a synchronous
+  // scroll.
+  //
+  // Even if this returns false, all wheel events in APZ-aware widgets must
+  // be sent through APZ so they are transformed correctly for TabParent.
+  static bool WillHandleWheelEvent(WidgetWheelEvent* aEvent);
+
 protected:
   // Protected destructor, to discourage deletion outside of Release():
   virtual ~APZCTreeManager();
diff --git a/layout/generic/nsGfxScrollFrame.cpp b/layout/generic/nsGfxScrollFrame.cpp
index 6aef854a7e..42bb0ff6b3 100644
--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -1089,13 +1089,12 @@ static bool IsFocused(nsIContent* aContent)
 bool
 ScrollFrameHelper::WantAsyncScroll() const
 {
-  nsRect scrollRange = GetScrollRange();
   ScrollbarStyles styles = GetScrollbarStylesFromFrame();
-
-  bool isVScrollable = (scrollRange.height > 0)
-                    && (styles.mVertical != NS_STYLE_OVERFLOW_HIDDEN);
-  bool isHScrollable = (scrollRange.width > 0)
-                    && (styles.mHorizontal != NS_STYLE_OVERFLOW_HIDDEN);
+  uint32_t directions = mOuter->GetScrollTargetFrame()->GetPerceivedScrollingDirections();
+  bool isVScrollable = !!(directions & nsIScrollableFrame::VERTICAL) &&
+                       (styles.mVertical != NS_STYLE_OVERFLOW_HIDDEN);
+  bool isHScrollable = !!(directions & nsIScrollableFrame::HORIZONTAL) &&
+                       (styles.mHorizontal != NS_STYLE_OVERFLOW_HIDDEN);
 
 #if defined(MOZ_B2G) || defined(MOZ_WIDGET_ANDROID)
   // Mobile platforms need focus to scroll.
diff --git a/layout/generic/test/mochitest.ini b/layout/generic/test/mochitest.ini
index f4f9832443..1c5830ea31 100644
--- a/layout/generic/test/mochitest.ini
+++ b/layout/generic/test/mochitest.ini
@@ -83,7 +83,7 @@ support-files = bug633762_iframe.html
 skip-if = (buildapp == 'b2g' && toolkit != 'gonk') #Bug 931116, b2g desktop specific, initial triage
 [test_bug748961.html]
 [test_bug784410.html]
-skip-if = (buildapp == 'b2g' && toolkit != 'gonk') #Bug 931116, b2g desktop specific, initial triage
+skip-if = buildapp == 'b2g' #Bug 931116, 1129060 no wheel events on b2g
 [test_bug785324.html]
 [test_bug791616.html]
 skip-if = buildapp == 'b2g' # b2g(Target should not have scrolled - got 114.10000610351562, expected 115.39999389648438) b2g-debug(Target should not have scrolled - got 114.10000610351562, expected 115.39999389648438) b2g-desktop(Target should not have scrolled - got 114.10000610351562, expected 115.39999389648438)
diff --git a/widget/PuppetWidget.cpp b/widget/PuppetWidget.cpp
index 9e79047b5c..5da72ce685 100644
--- a/widget/PuppetWidget.cpp
+++ b/widget/PuppetWidget.cpp
@@ -328,6 +328,30 @@ PuppetWidget::DispatchEvent(WidgetGUIEvent* event, nsEventStatus& aStatus)
 }
 
 
+nsEventStatus
+PuppetWidget::DispatchAPZAwareEvent(WidgetInputEvent* aEvent)
+{
+  if (!gfxPrefs::AsyncPanZoomEnabled()) {
+    nsEventStatus status = nsEventStatus_eIgnore;
+    DispatchEvent(aEvent, status);
+    return status;
+  }
+
+  if (!mTabChild) {
+    return nsEventStatus_eIgnore;
+  }
+
+  switch (aEvent->mClass) {
+    case eWheelEventClass:
+      mTabChild->SendSynthesizedMouseWheelEvent(*aEvent->AsWheelEvent());
+      break;
+    default:
+      MOZ_ASSERT_UNREACHABLE("unsupported event type");
+  }
+
+  return nsEventStatus_eIgnore;
+}
+
 NS_IMETHODIMP_(bool)
 PuppetWidget::ExecuteNativeKeyBinding(NativeKeyBindingsType aType,
                                       const mozilla::WidgetKeyboardEvent& aEvent,
diff --git a/widget/PuppetWidget.h b/widget/PuppetWidget.h
index 4a0eb1b4ec..864e6d81d7 100644
--- a/widget/PuppetWidget.h
+++ b/widget/PuppetWidget.h
@@ -128,6 +128,7 @@ public:
   void InitEvent(WidgetGUIEvent& aEvent, nsIntPoint* aPoint = nullptr);
 
   NS_IMETHOD DispatchEvent(WidgetGUIEvent* aEvent, nsEventStatus& aStatus) override;
+  nsEventStatus DispatchAPZAwareEvent(WidgetInputEvent* aEvent) override;
 
   NS_IMETHOD CaptureRollupEvents(nsIRollupListener* aListener,
                                  bool aDoCapture) override
diff --git a/widget/gonk/nsWindow.cpp b/widget/gonk/nsWindow.cpp
index b3cb8dabef..02d8e5e5b7 100644
--- a/widget/gonk/nsWindow.cpp
+++ b/widget/gonk/nsWindow.cpp
@@ -326,7 +326,7 @@ nsWindow::DispatchTouchEventForAPZ(const MultiTouchInput& aInput,
     // for "normal" flow. The event might get sent to the child process still,
     // but if it doesn't we need to notify the APZ of various things. All of
     // that happens in DispatchEventForAPZ
-    DispatchEventForAPZ(&event, aGuid, aInputBlockId);
+    ProcessUntransformedAPZEvent(&event, aGuid, aInputBlockId);
 }
 
 class DispatchTouchInputOnControllerThread : public Task
diff --git a/widget/gtk/nsWindow.cpp b/widget/gtk/nsWindow.cpp
index a0c9c083ea..af356ec84b 100644
--- a/widget/gtk/nsWindow.cpp
+++ b/widget/gtk/nsWindow.cpp
@@ -3249,19 +3249,7 @@ nsWindow::OnScrollEvent(GdkEventScroll *aEvent)
 
     wheelEvent.time = aEvent->time;
 
-    if (mAPZC) {
-        uint64_t inputBlockId = 0;
-        ScrollableLayerGuid guid;
-
-        nsEventStatus result = mAPZC->ReceiveInputEvent(*wheelEvent.AsWheelEvent(), &guid, &inputBlockId);
-        if (result == nsEventStatus_eConsumeNoDefault) {
-            return;
-        }
-        DispatchEventForAPZ(&wheelEvent, guid, inputBlockId);
-    } else {
-        nsEventStatus status;
-        DispatchEvent(&wheelEvent, status);
-    }
+    DispatchAPZAwareEvent(&wheelEvent);
 }
 
 void
diff --git a/widget/nsBaseWidget.cpp b/widget/nsBaseWidget.cpp
index 67e296d6be..bbda053fd1 100644
--- a/widget/nsBaseWidget.cpp
+++ b/widget/nsBaseWidget.cpp
@@ -973,9 +973,9 @@ void nsBaseWidget::ConfigureAPZCTreeManager()
 }
 
 nsEventStatus
-nsBaseWidget::DispatchEventForAPZ(WidgetGUIEvent* aEvent,
-                                  const ScrollableLayerGuid& aGuid,
-                                  uint64_t aInputBlockId)
+nsBaseWidget::ProcessUntransformedAPZEvent(WidgetInputEvent* aEvent,
+                                           const ScrollableLayerGuid& aGuid,
+                                           uint64_t aInputBlockId)
 {
   MOZ_ASSERT(NS_IsMainThread());
   InputAPZContext context(aGuid, aInputBlockId);
@@ -1015,6 +1015,25 @@ nsBaseWidget::DispatchEventForAPZ(WidgetGUIEvent* aEvent,
   return status;
 }
 
+nsEventStatus
+nsBaseWidget::DispatchAPZAwareEvent(WidgetInputEvent* aEvent)
+{
+  if (mAPZC) {
+    uint64_t inputBlockId = 0;
+    ScrollableLayerGuid guid;
+
+    nsEventStatus result = mAPZC->ReceiveInputEvent(*aEvent, &guid, &inputBlockId);
+    if (result == nsEventStatus_eConsumeNoDefault) {
+        return result;
+    }
+    return ProcessUntransformedAPZEvent(aEvent, guid, inputBlockId);
+  }
+
+  nsEventStatus status;
+  DispatchEvent(aEvent, status);
+  return status;
+}
+
 void
 nsBaseWidget::GetPreferredCompositorBackends(nsTArray<LayersBackend>& aHints)
 {
diff --git a/widget/nsBaseWidget.h b/widget/nsBaseWidget.h
index 259e47f42e..00165dcb72 100644
--- a/widget/nsBaseWidget.h
+++ b/widget/nsBaseWidget.h
@@ -231,6 +231,9 @@ public:
   NS_IMETHOD              UnregisterTouchWindow() override;
   NS_IMETHOD_(TextEventDispatcher*) GetTextEventDispatcher() override final;
 
+  // Dispatch an event that must be first be routed through APZ.
+  nsEventStatus DispatchAPZAwareEvent(mozilla::WidgetInputEvent* aEvent) MOZ_OVERRIDE;
+
   void NotifyWindowDestroyed();
   void NotifySizeMoveDone();
   void NotifyWindowMoved(int32_t aX, int32_t aY);
@@ -326,11 +329,10 @@ protected:
   virtual void ConfigureAPZCTreeManager();
   virtual already_AddRefed<GoannaContentController> CreateRootContentController();
 
-  // Dispatch an event that has been routed through APZ directly from the
-  // widget.
-  nsEventStatus DispatchEventForAPZ(mozilla::WidgetGUIEvent* aEvent,
-                                    const ScrollableLayerGuid& aGuid,
-                                    uint64_t aInputBlockId);
+  // Dispatch an event that has already been routed through APZ.
+  nsEventStatus ProcessUntransformedAPZEvent(mozilla::WidgetInputEvent* aEvent,
+                                             const ScrollableLayerGuid& aGuid,
+                                             uint64_t aInputBlockId);
 
   const nsIntRegion RegionFromArray(const nsTArray<nsIntRect>& aRects);
   void ArrayFromRegion(const nsIntRegion& aRegion, nsTArray<nsIntRect>& aRects);
diff --git a/widget/nsIWidget.h b/widget/nsIWidget.h
index 834a9976c3..be737c7073 100644
--- a/widget/nsIWidget.h
+++ b/widget/nsIWidget.h
@@ -1687,6 +1687,13 @@ class nsIWidget : public nsISupports {
     NS_IMETHOD DispatchEvent(mozilla::WidgetGUIEvent* event,
                              nsEventStatus & aStatus) = 0;
 
+    /**
+     * Dispatches an event that must be handled by APZ first, when APZ is
+     * enabled. If invoked in the child process, it is forwarded to the
+     * parent process synchronously.
+     */
+    virtual nsEventStatus DispatchAPZAwareEvent(mozilla::WidgetInputEvent* aEvent) = 0;
+
     /**
      * Enables the dropping of files to a widget (XXX this is temporary)
      *
diff --git a/widget/windows/nsWindow.cpp b/widget/windows/nsWindow.cpp
index 1f0e432452..b681dcb14e 100644
--- a/widget/windows/nsWindow.cpp
+++ b/widget/windows/nsWindow.cpp
@@ -3697,20 +3697,13 @@ bool nsWindow::DispatchKeyboardEvent(WidgetGUIEvent* event)
 
 bool nsWindow::DispatchScrollEvent(WidgetGUIEvent* aEvent)
 {
-  nsEventStatus status;
-
-  if (mAPZC && aEvent->mClass == eWheelEventClass) {
-    uint64_t inputBlockId = 0;
-    ScrollableLayerGuid guid;
-
-    nsEventStatus result = mAPZC->ReceiveInputEvent(*aEvent->AsWheelEvent(), &guid, &inputBlockId);
-    if (result == nsEventStatus_eConsumeNoDefault) {
-      return true;
-    }
-    status = DispatchEventForAPZ(aEvent, guid, inputBlockId);
-  } else {
+  if (aEvent->mClass != eWheelEventClass) {
+    nsEventStatus status;
     DispatchEvent(aEvent, status);
+    return ConvertStatus(status);
   }
+
+  nsEventStatus status = DispatchAPZAwareEvent(aEvent->AsInputEvent());
   return ConvertStatus(status);
 }