--- a/dom/events/EventStateManager.cpp
+++ b/dom/events/EventStateManager.cpp
@@ -3374,16 +3374,18 @@ EventStateManager::PostHandleEvent(nsPre
       // because if the scroll target is a plugin, the default action should be
       // chosen by the plugin rather than by our prefs.
       nsIFrame* frameToScroll =
         ComputeScrollTarget(mCurrentTarget, wheelEvent,
                             COMPUTE_DEFAULT_ACTION_TARGET);
       nsPluginFrame* pluginFrame = do_QueryFrame(frameToScroll);
       if (pluginFrame) {
         MOZ_ASSERT(pluginFrame->WantsToHandleWheelEventAsDefaultAction());
+        // Plugins should receive original values instead of adjusted values.
+        adjuster.CancelAdjustment();
         action = WheelPrefs::ACTION_SEND_TO_PLUGIN;
       }
 
       switch (action) {
         case WheelPrefs::ACTION_SCROLL:
         case WheelPrefs::ACTION_HORIZONTAL_SCROLL: {
           // For scrolling of default action, we should honor the mouse wheel
           // transaction.

--- a/dom/events/WheelHandlingHelper.cpp
+++ b/dom/events/WheelHandlingHelper.cpp
@@ -605,24 +605,30 @@ AutoWheelDeltaAdjuster::AutoWheelDeltaAd
     mWheelEvent.mOverflowDeltaY = 0.0;
     mWheelEvent.mLineOrPageDeltaX = mWheelEvent.mLineOrPageDeltaY;
     mWheelEvent.mLineOrPageDeltaY = 0;
     mWheelEvent.mDeltaValuesAdjustedForDefaultHandler = true;
     mTreatedVerticalWheelAsHorizontalScroll = true;
   }
 }
 
-AutoWheelDeltaAdjuster::~AutoWheelDeltaAdjuster()
+void AutoWheelDeltaAdjuster::CancelAdjustment()
 {
   if (mTreatedVerticalWheelAsHorizontalScroll &&
       mWheelEvent.mDeltaValuesAdjustedForDefaultHandler) {
     mWheelEvent.mDeltaY = mWheelEvent.mDeltaX;
     mWheelEvent.mDeltaX = mOldDeltaX;
     mWheelEvent.mDeltaZ = mOldDeltaZ;
     mWheelEvent.mOverflowDeltaY = mWheelEvent.mOverflowDeltaX;
     mWheelEvent.mOverflowDeltaX = mOldOverflowDeltaX;
     mWheelEvent.mLineOrPageDeltaY = mWheelEvent.mLineOrPageDeltaX;
     mWheelEvent.mLineOrPageDeltaX = mOldLineOrPageDeltaX;
     mWheelEvent.mDeltaValuesAdjustedForDefaultHandler = false;
+    mTreatedVerticalWheelAsHorizontalScroll = false;
   }
 }
 
+AutoWheelDeltaAdjuster::~AutoWheelDeltaAdjuster()
+{
+  CancelAdjustment();
+}
+
 } // namespace mozilla

--- a/dom/events/WheelHandlingHelper.h
+++ b/dom/events/WheelHandlingHelper.h
@@ -224,16 +224,17 @@ public:
    *                           modified for default handler.
    *                           Its mDeltaValuesAdjustedForDefaultHandler
    *                           must not be true because if it's true,
    *                           the event has already been adjusted the
    *                           delta values for default handler.
    */
   explicit AutoWheelDeltaAdjuster(WidgetWheelEvent& aWheelEvent);
   ~AutoWheelDeltaAdjuster();
+  void CancelAdjustment();
 
 private:
   WidgetWheelEvent& mWheelEvent;
   double mOldDeltaX;
   double mOldDeltaZ;
   double mOldOverflowDeltaX;
   int32_t mOldLineOrPageDeltaX;
   bool mTreatedVerticalWheelAsHorizontalScroll;