--- a/gfx/layers/apz/src/AsyncPanZoomController.cpp
+++ b/gfx/layers/apz/src/AsyncPanZoomController.cpp
@@ -1819,21 +1819,22 @@ AsyncPanZoomController::OnKeyboard(const
   if (mState != KEYBOARD_SCROLL) {
     CancelAnimation();
     SetState(KEYBOARD_SCROLL);
 
     nsPoint initialPosition = CSSPoint::ToAppUnits(mFrameMetrics.GetScrollOffset());
     StartAnimation(new KeyboardScrollAnimation(*this, initialPosition, aEvent.mAction.mType));
   }
 
-  // Cast velocity from ParentLayerPoints/ms to CSSPoints/ms then convert to
-  // appunits/second. We perform a cast to ParentLayerPoints/ms without a
-  // conversion so that the scroll duration isn't affected by zoom
+  // Convert velocity from ParentLayerPoints/ms to ParentLayerPoints/s and then
+  // to appunits/second.
   nsPoint velocity =
-    CSSPoint::ToAppUnits(CSSPoint(mX.GetVelocity(), mY.GetVelocity())) * 1000.0f;
+    CSSPoint::ToAppUnits(
+      ParentLayerPoint(mX.GetVelocity() * 1000.0f, mY.GetVelocity() * 1000.0f) /
+      mFrameMetrics.GetZoom());
 
   KeyboardScrollAnimation* animation = mAnimation->AsKeyboardScrollAnimation();
   MOZ_ASSERT(animation);
 
   animation->UpdateDestination(aEvent.mTimeStamp,
                                CSSPixel::ToAppUnits(destination),
                                nsSize(velocity.x, velocity.y));
 
@@ -2097,21 +2098,24 @@ nsEventStatus AsyncPanZoomController::On
 
         nsPoint initialPosition = CSSPoint::ToAppUnits(mFrameMetrics.GetScrollOffset());
         StartAnimation(new WheelScrollAnimation(
           *this, initialPosition, aEvent.mDeltaType));
       }
 
       nsPoint deltaInAppUnits =
         CSSPoint::ToAppUnits(delta / mFrameMetrics.GetZoom());
-      // Cast velocity from ParentLayerPoints/ms to CSSPoints/ms then convert to
-      // appunits/second. We perform a cast to ParentLayerPoints/ms without a
-      // conversion so that the scroll duration isn't affected by zoom
+
+      // Convert velocity from ParentLayerPoints/ms to ParentLayerPoints/s and
+      // then to appunits/second.
       nsPoint velocity =
-        CSSPoint::ToAppUnits(CSSPoint(mX.GetVelocity(), mY.GetVelocity())) * 1000.0f;
+        CSSPoint::ToAppUnits(
+          ParentLayerPoint(mX.GetVelocity() * 1000.0f,
+                           mY.GetVelocity() * 1000.0f) /
+          mFrameMetrics.GetZoom());
 
       WheelScrollAnimation* animation = mAnimation->AsWheelScrollAnimation();
       animation->UpdateDelta(aEvent.mTimeStamp, deltaInAppUnits, nsSize(velocity.x, velocity.y));
       break;
     }
   }
 
   return nsEventStatus_eConsumeNoDefault;
@@ -2856,21 +2860,24 @@ void AsyncPanZoomController::SmoothScrol
     APZC_LOG("%p updating destination on existing animation\n", this);
     RefPtr<SmoothScrollAnimation> animation(
       static_cast<SmoothScrollAnimation*>(mAnimation.get()));
     animation->SetDestination(CSSPoint::ToAppUnits(aDestination));
   } else {
     CancelAnimation();
     SetState(SMOOTH_SCROLL);
     nsPoint initialPosition = CSSPoint::ToAppUnits(mFrameMetrics.GetScrollOffset());
-    // Cast velocity from ParentLayerPoints/ms to CSSPoints/ms then convert to
-    // appunits/second. We perform a cast to ParentLayerPoints/ms without a
-    // conversion so that the scroll duration isn't affected by zoom
-    nsPoint initialVelocity = CSSPoint::ToAppUnits(CSSPoint(mX.GetVelocity(),
-                                                            mY.GetVelocity())) * 1000.0f;
+    // Convert velocity from ParentLayerPoints/ms to ParentLayerPoints/s and
+    // then to appunits/second.
+    nsPoint initialVelocity =
+      CSSPoint::ToAppUnits(
+        ParentLayerPoint(mX.GetVelocity() * 1000.0f,
+                          mY.GetVelocity() * 1000.0f) /
+        mFrameMetrics.GetZoom());
+
     nsPoint destination = CSSPoint::ToAppUnits(aDestination);
 
     StartAnimation(new SmoothScrollAnimation(*this,
                                              initialPosition, initialVelocity,
                                              destination,
                                              gfxPrefs::ScrollBehaviorSpringConstant(),
                                              gfxPrefs::ScrollBehaviorDampingRatio()));
   }

--- a/gfx/layers/apz/src/GenericScrollAnimation.cpp
+++ b/gfx/layers/apz/src/GenericScrollAnimation.cpp
@@ -69,21 +69,22 @@ GenericScrollAnimation::DoSample(FrameMe
                         : PositionAt(now);
   ParentLayerPoint displacement =
     (CSSPoint::FromAppUnits(sampledDest) - aFrameMetrics.GetScrollOffset()) * zoom;
 
   if (finished) {
     mApzc.mX.SetVelocity(0);
     mApzc.mY.SetVelocity(0);
   } else if (!IsZero(displacement)) {
-    // Velocity is measured in ParentLayerCoords / Milliseconds
-    float xVelocity = displacement.x / aDelta.ToMilliseconds();
-    float yVelocity = displacement.y / aDelta.ToMilliseconds();
-    mApzc.mX.SetVelocity(xVelocity);
-    mApzc.mY.SetVelocity(yVelocity);
+    // Convert velocity from AppUnits/Seconds to ParentLayerCoords/Milliseconds
+    nsSize velocity = VelocityAt(now);
+    ParentLayerPoint velocityPL =
+      CSSPoint::FromAppUnits(nsPoint(velocity.width, velocity.height)) * zoom;
+    mApzc.mX.SetVelocity(velocityPL.x / 1000.0);
+    mApzc.mY.SetVelocity(velocityPL.y / 1000.0);
   }
 
   // Note: we ignore overscroll for generic animations.
   ParentLayerPoint adjustedOffset, overscroll;
   mApzc.mX.AdjustDisplacement(displacement.x, adjustedOffset.x, overscroll.x);
   mApzc.mY.AdjustDisplacement(displacement.y, adjustedOffset.y, overscroll.y,
                               mForceVerticalOverscroll);