diff --git a/dom/events/EventStateManager.cpp b/dom/events/EventStateManager.cpp
index 9ec8d4533835..01ee68c09616 100644
--- a/dom/events/EventStateManager.cpp
+++ b/dom/events/EventStateManager.cpp
@@ -2430,7 +2430,7 @@ EventStateManager::DoScrollText(nsIScrollableFrame* aScrollableFrame,
     actualDevPixelScrollAmount.y = 0;
   }
 
-  nsIScrollableFrame::ScrollSnapMode snapMode = nsIScrollableFrame::DISABLE_SNAP;
+  nsIScrollbarMediator::ScrollSnapMode snapMode = nsIScrollbarMediator::DISABLE_SNAP;
   nsIAtom* origin = nullptr;
   switch (aEvent->deltaMode) {
     case nsIDOMWheelEvent::DOM_DELTA_LINE:
diff --git a/layout/generic/nsGfxScrollFrame.cpp b/layout/generic/nsGfxScrollFrame.cpp
index b2c263cd5488..d21e791ca627 100644
--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -1126,21 +1126,24 @@ GetOnePixelRangeAroundPoint(nsPoint aPoint, bool aIsHorizontal)
 }
 
 void
-ScrollFrameHelper::ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection)
+ScrollFrameHelper::ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                                nsIScrollbarMediator::ScrollSnapMode aSnap)
 {
   ScrollByUnit(aScrollbar, nsIScrollableFrame::SMOOTH, aDirection,
-               nsIScrollableFrame::PAGES);
+               nsIScrollableFrame::PAGES, aSnap);
 }
 
 void
-ScrollFrameHelper::ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection)
+ScrollFrameHelper::ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                                 nsIScrollbarMediator::ScrollSnapMode aSnap)
 {
   ScrollByUnit(aScrollbar, nsIScrollableFrame::INSTANT, aDirection,
-               nsIScrollableFrame::WHOLE);
+               nsIScrollableFrame::WHOLE, aSnap);
 }
 
 void
-ScrollFrameHelper::ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection)
+ScrollFrameHelper::ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                                nsIScrollbarMediator::ScrollSnapMode aSnap)
 {
   bool isHorizontal = aScrollbar->IsHorizontal();
   nsIntPoint delta;
@@ -1157,7 +1160,8 @@ ScrollFrameHelper::ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection
   }
   nsIntPoint overflow;
   ScrollBy(delta, nsIScrollableFrame::LINES, nsIScrollableFrame::SMOOTH,
-           &overflow, nsGkAtoms::other);
+           &overflow, nsGkAtoms::other, nsIScrollableFrame::NOT_MOMENTUM,
+           aSnap);
 }
 
 void
@@ -1192,11 +1196,24 @@ ScrollFrameHelper::ThumbMoved(nsScrollbarFrame* aScrollbar,
   ScrollTo(dest, nsIScrollableFrame::INSTANT, &allowedRange);
 }
 
+void
+ScrollFrameHelper::ScrollbarReleased(nsScrollbarFrame* aScrollbar)
+{
+  // Scrollbar scrolling does not result in fling gestures, clear any
+  // accumulated velocity
+  mVelocityQueue.Reset();
+
+  // Perform scroll snapping, if needed.  Scrollbar movement uses the same
+  // smooth scrolling animation as keyboard scrolling.
+  ScrollSnap(mDestination, nsIScrollableFrame::SMOOTH);
+}
+
 void
 ScrollFrameHelper::ScrollByUnit(nsScrollbarFrame* aScrollbar,
                                 nsIScrollableFrame::ScrollMode aMode,
                                 int32_t aDirection,
-                                nsIScrollableFrame::ScrollUnit aUnit)
+                                nsIScrollableFrame::ScrollUnit aUnit,
+                                nsIScrollbarMediator::ScrollSnapMode aSnap)
 {
   MOZ_ASSERT(aScrollbar != nullptr);
   bool isHorizontal = aScrollbar->IsHorizontal();
@@ -1207,7 +1224,8 @@ ScrollFrameHelper::ScrollByUnit(nsScrollbarFrame* aScrollbar,
     delta.y = aDirection;
   }
   nsIntPoint overflow;
-  ScrollBy(delta, aUnit, aMode, &overflow, nsGkAtoms::other);
+  ScrollBy(delta, aUnit, aMode, &overflow, nsGkAtoms::other,
+           nsIScrollableFrame::NOT_MOMENTUM, aSnap);
 }
 
 nsresult
@@ -2079,7 +2097,7 @@ ScrollFrameHelper::ScrollToWithOrigin(nsPoint aScrollPosition,
                                           nsIScrollableFrame::ScrollMode aMode,
                                           nsIAtom *aOrigin,
                                           const nsRect* aRange,
-                                          nsIScrollableFrame::ScrollSnapMode aSnap)
+                                          nsIScrollbarMediator::ScrollSnapMode aSnap)
 {
 
   if (aSnap == nsIScrollableFrame::ENABLE_SNAP) {
@@ -3348,7 +3366,7 @@ ScrollFrameHelper::ScrollBy(nsIntPoint aDelta,
                             nsIntPoint* aOverflow,
                             nsIAtom *aOrigin,
                             nsIScrollableFrame::ScrollMomentum aMomentum,
-                            nsIScrollableFrame::ScrollSnapMode aSnap)
+                            nsIScrollbarMediator::ScrollSnapMode aSnap)
 {
   // When a smooth scroll is being processed on a frame, mouse wheel and trackpad
   // momentum scroll event updates must notcancel the SMOOTH or SMOOTH_MSD
@@ -3480,7 +3498,7 @@ ScrollFrameHelper::ScrollBy(nsIntPoint aDelta,
 }
 
 void
-ScrollFrameHelper::ScrollSnap()
+ScrollFrameHelper::ScrollSnap(nsIScrollableFrame::ScrollMode aMode)
 {
   float flingSensitivity = gfxPrefs::ScrollSnapPredictionSensitivity();
   int maxVelocity = gfxPrefs::ScrollSnapPredictionMaxVelocity();
@@ -3493,7 +3511,7 @@ ScrollFrameHelper::ScrollSnap()
   predictedOffset.Clamp(maxOffset);
   nsPoint pos = GetScrollPosition();
   nsPoint destinationPos = pos + predictedOffset;
-  ScrollSnap(destinationPos);
+  ScrollSnap(destinationPos, aMode);
 }
 
 void
@@ -3503,7 +3521,8 @@ ScrollFrameHelper::FlingSnap(const mozilla::CSSPoint& aDestination)
 }
 
 void
-ScrollFrameHelper::ScrollSnap(const nsPoint &aDestination)
+ScrollFrameHelper::ScrollSnap(const nsPoint &aDestination,
+                              nsIScrollableFrame::ScrollMode aMode)
 {
   nsRect scrollRange = GetScrollRangeForClamping();
   nsPoint pos = GetScrollPosition();
@@ -3511,7 +3530,7 @@ ScrollFrameHelper::ScrollSnap(const nsPoint &aDestination)
   if (GetSnapPointForDestination(nsIScrollableFrame::DEVICE_PIXELS,
                                                  pos,
                                                  snapDestination)) {
-    ScrollTo(snapDestination, nsIScrollableFrame::SMOOTH_MSD);
+    ScrollTo(snapDestination, aMode);
   }
 }
 
diff --git a/layout/generic/nsGfxScrollFrame.h b/layout/generic/nsGfxScrollFrame.h
index cd4c4e996907..10838c38eb6c 100644
--- a/layout/generic/nsGfxScrollFrame.h
+++ b/layout/generic/nsGfxScrollFrame.h
@@ -181,8 +181,9 @@ public:
   void SetResolution(const gfxSize& aResolution);
   void SetResolutionAndScaleTo(const gfxSize& aResolution);
   void FlingSnap(const mozilla::CSSPoint& aDestination);
-  void ScrollSnap();
-  void ScrollSnap(const nsPoint &aDestination);
+  void ScrollSnap(nsIScrollableFrame::ScrollMode aMode = nsIScrollableFrame::SMOOTH_MSD);
+  void ScrollSnap(const nsPoint &aDestination,
+                  nsIScrollableFrame::ScrollMode aMode = nsIScrollableFrame::SMOOTH_MSD);
 
 protected:
   nsRect GetScrollRangeForClamping() const;
@@ -200,7 +201,8 @@ public:
    */
   void ScrollTo(nsPoint aScrollPosition, nsIScrollableFrame::ScrollMode aMode,
                 const nsRect* aRange = nullptr,
-                nsIScrollableFrame::ScrollSnapMode aSnap = nsIScrollableFrame::DISABLE_SNAP) {
+                nsIScrollbarMediator::ScrollSnapMode aSnap
+                  = nsIScrollbarMediator::DISABLE_SNAP) {
     ScrollToWithOrigin(aScrollPosition, aMode, nsGkAtoms::other, aRange,
                        aSnap);
   }
@@ -229,7 +231,8 @@ public:
                 nsIScrollableFrame::ScrollMode aMode, nsIntPoint* aOverflow,
                 nsIAtom* aOrigin = nullptr,
                 nsIScrollableFrame::ScrollMomentum aMomentum = nsIScrollableFrame::NOT_MOMENTUM,
-                nsIScrollableFrame::ScrollSnapMode aSnap = nsIScrollableFrame::DISABLE_SNAP);
+                nsIScrollbarMediator::ScrollSnapMode aSnap
+                  = nsIScrollbarMediator::DISABLE_SNAP);
   /**
    * @note This method might destroy the frame, pres shell and other objects.
    */
@@ -380,17 +383,26 @@ public:
                            nsTArray<FrameMetrics>* aOutput) const;
 
   // nsIScrollbarMediator
-  void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection);
-  void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection);
-  void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection);
+  void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                    nsIScrollbarMediator::ScrollSnapMode aSnap
+                      = nsIScrollbarMediator::DISABLE_SNAP);
+  void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                     nsIScrollbarMediator::ScrollSnapMode aSnap
+                       = nsIScrollbarMediator::DISABLE_SNAP);
+  void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                    nsIScrollbarMediator::ScrollSnapMode aSnap
+                      = nsIScrollbarMediator::DISABLE_SNAP);
   void RepeatButtonScroll(nsScrollbarFrame* aScrollbar);
   void ThumbMoved(nsScrollbarFrame* aScrollbar,
                   nscoord aOldPos,
                   nscoord aNewPos);
+  void ScrollbarReleased(nsScrollbarFrame* aScrollbar);
   void ScrollByUnit(nsScrollbarFrame* aScrollbar,
                     nsIScrollableFrame::ScrollMode aMode,
                     int32_t aDirection,
-                    nsIScrollableFrame::ScrollUnit aUnit);
+                    nsIScrollableFrame::ScrollUnit aUnit,
+                    nsIScrollbarMediator::ScrollSnapMode aSnap
+                      = nsIScrollbarMediator::DISABLE_SNAP);
 
   // owning references to the nsIAnonymousContentCreator-built content
   nsCOMPtr<nsIContent> mHScrollbarContent;
@@ -520,7 +532,8 @@ protected:
                           nsIScrollableFrame::ScrollMode aMode,
                           nsIAtom *aOrigin, // nullptr indicates "other" origin
                           const nsRect* aRange,
-                          nsIScrollableFrame::ScrollSnapMode aSnap = nsIScrollableFrame::DISABLE_SNAP);
+                          nsIScrollbarMediator::ScrollSnapMode aSnap
+                            = nsIScrollbarMediator::DISABLE_SNAP);
 
   void CompleteAsyncScroll(const nsRect &aRange, nsIAtom* aOrigin = nullptr);
 
@@ -709,7 +722,8 @@ public:
    */
   virtual void ScrollTo(nsPoint aScrollPosition, ScrollMode aMode,
                         const nsRect* aRange = nullptr,
-                        nsIScrollableFrame::ScrollSnapMode aSnap = nsIScrollableFrame::DISABLE_SNAP)
+                        nsIScrollbarMediator::ScrollSnapMode aSnap
+                          = nsIScrollbarMediator::DISABLE_SNAP)
                         MOZ_OVERRIDE {
     mHelper.ScrollTo(aScrollPosition, aMode, aRange, aSnap);
   }
@@ -737,7 +751,8 @@ public:
   virtual void ScrollBy(nsIntPoint aDelta, ScrollUnit aUnit, ScrollMode aMode,
                         nsIntPoint* aOverflow, nsIAtom* aOrigin = nullptr,
                         nsIScrollableFrame::ScrollMomentum aMomentum = nsIScrollableFrame::NOT_MOMENTUM,
-                        nsIScrollableFrame::ScrollSnapMode aSnap = nsIScrollableFrame::DISABLE_SNAP)
+                        nsIScrollbarMediator::ScrollSnapMode aSnap
+                          = nsIScrollbarMediator::DISABLE_SNAP)
                         MOZ_OVERRIDE {
     mHelper.ScrollBy(aDelta, aUnit, aMode, aOverflow, aOrigin, aMomentum, aSnap);
   }
@@ -845,14 +860,20 @@ public:
   virtual nsIAtom* GetType() const MOZ_OVERRIDE;
 
   // nsIScrollbarMediator
-  virtual void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection) MOZ_OVERRIDE {
-    mHelper.ScrollByPage(aScrollbar, aDirection);
+  virtual void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                            nsIScrollbarMediator::ScrollSnapMode aSnap
+                              = nsIScrollbarMediator::DISABLE_SNAP) MOZ_OVERRIDE {
+    mHelper.ScrollByPage(aScrollbar, aDirection, aSnap);
   }
-  virtual void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection) MOZ_OVERRIDE {
-    mHelper.ScrollByWhole(aScrollbar, aDirection);
+  virtual void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                             nsIScrollbarMediator::ScrollSnapMode aSnap
+                               = nsIScrollbarMediator::DISABLE_SNAP) MOZ_OVERRIDE {
+    mHelper.ScrollByWhole(aScrollbar, aDirection, aSnap);
   }
-  virtual void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection) MOZ_OVERRIDE {
-    mHelper.ScrollByLine(aScrollbar, aDirection);
+  virtual void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                            nsIScrollbarMediator::ScrollSnapMode aSnap
+                              = nsIScrollbarMediator::DISABLE_SNAP) MOZ_OVERRIDE {
+    mHelper.ScrollByLine(aScrollbar, aDirection, aSnap);
   }
   virtual void RepeatButtonScroll(nsScrollbarFrame* aScrollbar) MOZ_OVERRIDE {
     mHelper.RepeatButtonScroll(aScrollbar);
@@ -862,6 +883,9 @@ public:
                           nscoord aNewPos) MOZ_OVERRIDE {
     mHelper.ThumbMoved(aScrollbar, aOldPos, aNewPos);
   }
+  virtual void ScrollbarReleased(nsScrollbarFrame* aScrollbar) MOZ_OVERRIDE {
+    mHelper.ScrollbarReleased(aScrollbar);
+  }
   virtual void VisibilityChanged(bool aVisible) MOZ_OVERRIDE {}
   virtual nsIFrame* GetScrollbarBox(bool aVertical) MOZ_OVERRIDE {
     return mHelper.GetScrollbarBox(aVertical);
@@ -1090,7 +1114,8 @@ public:
    */
   virtual void ScrollTo(nsPoint aScrollPosition, ScrollMode aMode,
                         const nsRect* aRange = nullptr,
-                        ScrollSnapMode aSnap = nsIScrollableFrame::DISABLE_SNAP) MOZ_OVERRIDE {
+                        ScrollSnapMode aSnap = nsIScrollbarMediator::DISABLE_SNAP)
+                        MOZ_OVERRIDE {
     mHelper.ScrollTo(aScrollPosition, aMode, aRange, aSnap);
   }
   /**
@@ -1114,7 +1139,8 @@ public:
   virtual void ScrollBy(nsIntPoint aDelta, ScrollUnit aUnit, ScrollMode aMode,
                         nsIntPoint* aOverflow, nsIAtom* aOrigin = nullptr,
                         nsIScrollableFrame::ScrollMomentum aMomentum = nsIScrollableFrame::NOT_MOMENTUM,
-                        nsIScrollableFrame::ScrollSnapMode aSnap = nsIScrollableFrame::DISABLE_SNAP)
+                        nsIScrollbarMediator::ScrollSnapMode aSnap
+                          = nsIScrollbarMediator::DISABLE_SNAP)
                         MOZ_OVERRIDE {
     mHelper.ScrollBy(aDelta, aUnit, aMode, aOverflow, aOrigin, aMomentum, aSnap);
   }
@@ -1229,14 +1255,20 @@ public:
     return nsBoxFrame::IsFrameOfType(aFlags);
   }
 
-  virtual void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection) MOZ_OVERRIDE {
-    mHelper.ScrollByPage(aScrollbar, aDirection);
+  virtual void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                            nsIScrollbarMediator::ScrollSnapMode aSnap
+                              = nsIScrollbarMediator::DISABLE_SNAP) MOZ_OVERRIDE {
+    mHelper.ScrollByPage(aScrollbar, aDirection, aSnap);
   }
-  virtual void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection) MOZ_OVERRIDE {
-    mHelper.ScrollByWhole(aScrollbar, aDirection);
+  virtual void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                             nsIScrollbarMediator::ScrollSnapMode aSnap
+                               = nsIScrollbarMediator::DISABLE_SNAP) MOZ_OVERRIDE {
+    mHelper.ScrollByWhole(aScrollbar, aDirection, aSnap);
   }
-  virtual void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection) MOZ_OVERRIDE {
-    mHelper.ScrollByLine(aScrollbar, aDirection);
+  virtual void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                            nsIScrollbarMediator::ScrollSnapMode aSnap
+                              = nsIScrollbarMediator::DISABLE_SNAP) MOZ_OVERRIDE {
+    mHelper.ScrollByLine(aScrollbar, aDirection, aSnap);
   }
   virtual void RepeatButtonScroll(nsScrollbarFrame* aScrollbar) MOZ_OVERRIDE {
     mHelper.RepeatButtonScroll(aScrollbar);
@@ -1246,6 +1278,9 @@ public:
                           nscoord aNewPos) MOZ_OVERRIDE {
     mHelper.ThumbMoved(aScrollbar, aOldPos, aNewPos);
   }
+  virtual void ScrollbarReleased(nsScrollbarFrame* aScrollbar) MOZ_OVERRIDE {
+    mHelper.ScrollbarReleased(aScrollbar);
+  }
   virtual void VisibilityChanged(bool aVisible) MOZ_OVERRIDE {}
   virtual nsIFrame* GetScrollbarBox(bool aVertical) MOZ_OVERRIDE {
     return mHelper.GetScrollbarBox(aVertical);
diff --git a/layout/generic/nsIScrollableFrame.h b/layout/generic/nsIScrollableFrame.h
index 20ae8638bf22..6a3cdc65a5ab 100644
--- a/layout/generic/nsIScrollableFrame.h
+++ b/layout/generic/nsIScrollableFrame.h
@@ -207,13 +207,6 @@ public:
    * been started since the last actual user input.
    */
   enum ScrollMomentum { NOT_MOMENTUM, SYNTHESIZED_MOMENTUM_EVENT };
-  /**
-   * When set to ENABLE_SNAP, additional scrolling will be performed after the
-   * scroll operation to maintain the constraints set by CSS Scroll snapping.
-   * The additional scrolling may include asynchronous smooth scrolls that
-   * continue to animate after the initial scroll position has been set.
-   */
-  enum ScrollSnapMode { DISABLE_SNAP, ENABLE_SNAP };
   /**
    * @note This method might destroy the frame, pres shell and other objects.
    * Clamps aScrollPosition to GetScrollRange and sets the scroll position
@@ -225,7 +218,8 @@ public:
    */
   virtual void ScrollTo(nsPoint aScrollPosition, ScrollMode aMode,
                         const nsRect* aRange = nullptr,
-                        ScrollSnapMode aSnap = DISABLE_SNAP) = 0;
+                        nsIScrollbarMediator::ScrollSnapMode aSnap
+                          = nsIScrollbarMediator::DISABLE_SNAP) = 0;
   /**
    * @note This method might destroy the frame, pres shell and other objects.
    * Scrolls to a particular position in integer CSS pixels.
@@ -280,7 +274,8 @@ public:
                         nsIntPoint* aOverflow = nullptr,
                         nsIAtom* aOrigin = nullptr,
                         ScrollMomentum aMomentum = NOT_MOMENTUM,
-                        ScrollSnapMode aSnap = DISABLE_SNAP) = 0;
+                        nsIScrollbarMediator::ScrollSnapMode aSnap
+                          = nsIScrollbarMediator::DISABLE_SNAP) = 0;
 
   /**
    * Perform scroll snapping, possibly resulting in a smooth scroll to
diff --git a/layout/xul/nsIScrollbarMediator.h b/layout/xul/nsIScrollbarMediator.h
index f6730081660f..e4de93cc79ad 100644
--- a/layout/xul/nsIScrollbarMediator.h
+++ b/layout/xul/nsIScrollbarMediator.h
@@ -24,14 +24,25 @@ public:
    * aDirection is either -1, 0, or 1.
    */
 
+  /**
+   * When set to ENABLE_SNAP, additional scrolling will be performed after the
+   * scroll operation to maintain the constraints set by CSS Scroll snapping.
+   * The additional scrolling may include asynchronous smooth scrolls that
+   * continue to animate after the initial scroll position has been set.
+   */
+  enum ScrollSnapMode { DISABLE_SNAP, ENABLE_SNAP };
+
   /**
    * One of the following three methods is called when the scrollbar's button is
    * clicked.
    * @note These methods might destroy the frame, pres shell, and other objects.
    */
-  virtual void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection) = 0;
-  virtual void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection) = 0;
-  virtual void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection) = 0;
+  virtual void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                            ScrollSnapMode aSnap = DISABLE_SNAP) = 0;
+  virtual void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                            ScrollSnapMode aSnap = DISABLE_SNAP) = 0;
+  virtual void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                            ScrollSnapMode aSnap = DISABLE_SNAP) = 0;
   /**
    * RepeatButtonScroll is called when the scrollbar's button is held down. When the
    * button is first clicked the increment is set; RepeatButtonScroll adds this
@@ -49,6 +60,11 @@ public:
   virtual void ThumbMoved(nsScrollbarFrame* aScrollbar,
                           nscoord aOldPos,
                           nscoord aNewPos) = 0;
+  /**
+   * Called when the scroll bar thumb, slider, or any other component is
+   * released.
+   */
+  virtual void ScrollbarReleased(nsScrollbarFrame* aScrollbar) = 0;
   virtual void VisibilityChanged(bool aVisible) = 0;
 
   /**
diff --git a/layout/xul/nsListBoxBodyFrame.cpp b/layout/xul/nsListBoxBodyFrame.cpp
index 81d139af5fcd..5d867b3317dc 100644
--- a/layout/xul/nsListBoxBodyFrame.cpp
+++ b/layout/xul/nsListBoxBodyFrame.cpp
@@ -326,8 +326,10 @@ nsListBoxBodyFrame::GetPrefSize(nsBoxLayoutState& aBoxLayoutState)
 ///////////// nsIScrollbarMediator ///////////////
 
 void
-nsListBoxBodyFrame::ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection)
+nsListBoxBodyFrame::ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                                 nsIScrollbarMediator::ScrollSnapMode aSnap)
 {
+  // CSS Scroll Snapping is not enabled for XUL, aSnap is ignored
   MOZ_ASSERT(aScrollbar != nullptr);
   aScrollbar->SetIncrementToPage(aDirection);
   nsWeakFrame weakFrame(this);
@@ -339,8 +341,10 @@ nsListBoxBodyFrame::ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirectio
 }
 
 void
-nsListBoxBodyFrame::ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection)
+nsListBoxBodyFrame::ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                                  nsIScrollbarMediator::ScrollSnapMode aSnap)
 {
+  // CSS Scroll Snapping is not enabled for XUL, aSnap is ignored
   MOZ_ASSERT(aScrollbar != nullptr);
   aScrollbar->SetIncrementToWhole(aDirection);
   nsWeakFrame weakFrame(this);
@@ -352,8 +356,10 @@ nsListBoxBodyFrame::ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirecti
 }
 
 void
-nsListBoxBodyFrame::ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection)
+nsListBoxBodyFrame::ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                                 nsIScrollbarMediator::ScrollSnapMode aSnap)
 {
+  // CSS Scroll Snapping is not enabled for XUL, aSnap is ignored
   MOZ_ASSERT(aScrollbar != nullptr);
   aScrollbar->SetIncrementToLine(aDirection);
   nsWeakFrame weakFrame(this);
diff --git a/layout/xul/nsListBoxBodyFrame.h b/layout/xul/nsListBoxBodyFrame.h
index a5e20f7efa57..41e4ac170f7d 100644
--- a/layout/xul/nsListBoxBodyFrame.h
+++ b/layout/xul/nsListBoxBodyFrame.h
@@ -54,13 +54,20 @@ public:
   virtual nsresult AttributeChanged(int32_t aNameSpaceID, nsIAtom* aAttribute, int32_t aModType) MOZ_OVERRIDE;
 
   // nsIScrollbarMediator
-  virtual void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection) MOZ_OVERRIDE;
-  virtual void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection) MOZ_OVERRIDE;
-  virtual void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection) MOZ_OVERRIDE;
+  virtual void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                            nsIScrollbarMediator::ScrollSnapMode snapMode
+                              = nsIScrollbarMediator::DISABLE_SNAP) MOZ_OVERRIDE;
+  virtual void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                             nsIScrollbarMediator::ScrollSnapMode snapMode
+                               = nsIScrollbarMediator::DISABLE_SNAP) MOZ_OVERRIDE;
+  virtual void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                            nsIScrollbarMediator::ScrollSnapMode snapMode
+                              = nsIScrollbarMediator::DISABLE_SNAP) MOZ_OVERRIDE;
   virtual void RepeatButtonScroll(nsScrollbarFrame* aScrollbar) MOZ_OVERRIDE;
   virtual void ThumbMoved(nsScrollbarFrame* aScrollbar,
                           int32_t aOldPos,
                           int32_t aNewPos) MOZ_OVERRIDE;
+  virtual void ScrollbarReleased(nsScrollbarFrame* aScrollbar) MOZ_OVERRIDE {}
   virtual void VisibilityChanged(bool aVisible) MOZ_OVERRIDE;
   virtual nsIFrame* GetScrollbarBox(bool aVertical) MOZ_OVERRIDE;
   virtual void ScrollbarActivityStarted() const MOZ_OVERRIDE {}
diff --git a/layout/xul/nsScrollbarButtonFrame.cpp b/layout/xul/nsScrollbarButtonFrame.cpp
index 52ccaf488889..193a477f233f 100644
--- a/layout/xul/nsScrollbarButtonFrame.cpp
+++ b/layout/xul/nsScrollbarButtonFrame.cpp
@@ -141,19 +141,19 @@ nsScrollbarButtonFrame::HandleButtonPress(nsPresContext* aPresContext,
     case 0:
       sb->SetIncrementToLine(direction);
       if (m) {
-        m->ScrollByLine(sb, direction);
+        m->ScrollByLine(sb, direction, nsIScrollbarMediator::ENABLE_SNAP);
       }
       break;
     case 1:
       sb->SetIncrementToPage(direction);
       if (m) {
-        m->ScrollByPage(sb, direction);
+        m->ScrollByPage(sb, direction, nsIScrollbarMediator::ENABLE_SNAP);
       }
       break;
     case 2:
       sb->SetIncrementToWhole(direction);
       if (m) {
-        m->ScrollByWhole(sb, direction);
+        m->ScrollByWhole(sb, direction, nsIScrollbarMediator::ENABLE_SNAP);
       }
       break;
     case 3:
@@ -187,6 +187,15 @@ nsScrollbarButtonFrame::HandleRelease(nsPresContext* aPresContext,
   // we're not active anymore
   mContent->UnsetAttr(kNameSpaceID_None, nsGkAtoms::active, true);
   StopRepeat();
+  nsIFrame* scrollbar;
+  GetParentWithTag(nsGkAtoms::scrollbar, this, scrollbar);
+  nsScrollbarFrame* sb = do_QueryFrame(scrollbar);
+  if (sb) {
+    nsIScrollbarMediator* m = sb->GetScrollbarMediator();
+    if (m) {
+      m->ScrollbarReleased(sb);
+    }
+  }
   return NS_OK;
 }
 
diff --git a/layout/xul/nsSliderFrame.cpp b/layout/xul/nsSliderFrame.cpp
index 4093da5c8061..2736dc48dede 100644
--- a/layout/xul/nsSliderFrame.cpp
+++ b/layout/xul/nsSliderFrame.cpp
@@ -264,7 +264,8 @@ nsSliderFrame::AttributeChanged(int32_t aNameSpaceID,
           nsIScrollbarMediator* mediator = scrollbarFrame->GetScrollbarMediator();
           scrollbarFrame->SetIncrementToWhole(direction);
           if (mediator) {
-            mediator->ScrollByWhole(scrollbarFrame, direction);
+            mediator->ScrollByWhole(scrollbarFrame, direction,
+                                    nsIScrollbarMediator::ENABLE_SNAP);
           }
         }
         // 'this' might be destroyed here
@@ -1153,6 +1154,14 @@ nsSliderFrame::HandleRelease(nsPresContext* aPresContext,
 {
   StopRepeat();
 
+  nsIFrame* scrollbar = GetScrollbar();
+  nsScrollbarFrame* sb = do_QueryFrame(scrollbar);
+  if (sb) {
+    nsIScrollbarMediator* m = sb->GetScrollbarMediator();
+    if (m) {
+      m->ScrollbarReleased(sb);
+    }
+  }
   return NS_OK;
 }
 
@@ -1261,7 +1270,7 @@ nsSliderFrame::PageScroll(nscoord aChange)
     nsIScrollbarMediator* m = sb->GetScrollbarMediator();
     sb->SetIncrementToPage(aChange);
     if (m) {
-      m->ScrollByPage(sb, aChange);
+      m->ScrollByPage(sb, aChange, nsIScrollbarMediator::ENABLE_SNAP);
       return;
     }
   }
diff --git a/layout/xul/tree/nsTreeBodyFrame.cpp b/layout/xul/tree/nsTreeBodyFrame.cpp
index 5f5389426ba3..246ab07a8e47 100644
--- a/layout/xul/tree/nsTreeBodyFrame.cpp
+++ b/layout/xul/tree/nsTreeBodyFrame.cpp
@@ -4200,23 +4200,29 @@ nsTreeBodyFrame::ScrollHorzInternal(const ScrollParts& aParts, int32_t aPosition
 }
 
 void
-nsTreeBodyFrame::ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection)
+nsTreeBodyFrame::ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                              nsIScrollbarMediator::ScrollSnapMode aSnap)
 {
+  // CSS Scroll Snapping is not enabled for XUL, aSnap is ignored
   MOZ_ASSERT(aScrollbar != nullptr);
   ScrollByPages(aDirection);
 }
 
 void
-nsTreeBodyFrame::ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection)
+nsTreeBodyFrame::ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                               nsIScrollbarMediator::ScrollSnapMode aSnap)
 {
+  // CSS Scroll Snapping is not enabled for XUL, aSnap is ignored
   MOZ_ASSERT(aScrollbar != nullptr); 
   int32_t newIndex = aDirection < 0 ? 0 : mTopRowIndex;
   ScrollToRow(newIndex);
 }
 
 void
-nsTreeBodyFrame::ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection)
+nsTreeBodyFrame::ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                              nsIScrollbarMediator::ScrollSnapMode aSnap)
 {
+  // CSS Scroll Snapping is not enabled for XUL, aSnap is ignored
   MOZ_ASSERT(aScrollbar != nullptr);
   ScrollByLines(aDirection);
 }
diff --git a/layout/xul/tree/nsTreeBodyFrame.h b/layout/xul/tree/nsTreeBodyFrame.h
index 8f8c29d18e44..4b9fa16beac6 100644
--- a/layout/xul/tree/nsTreeBodyFrame.h
+++ b/layout/xul/tree/nsTreeBodyFrame.h
@@ -133,13 +133,20 @@ public:
   virtual bool PseudoMatches(nsCSSSelector* aSelector) MOZ_OVERRIDE;
 
   // nsIScrollbarMediator
-  virtual void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection) MOZ_OVERRIDE;
-  virtual void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection) MOZ_OVERRIDE;
-  virtual void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection) MOZ_OVERRIDE;
+  virtual void ScrollByPage(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                            nsIScrollbarMediator::ScrollSnapMode aSnap
+                              = nsIScrollbarMediator::DISABLE_SNAP) MOZ_OVERRIDE;
+  virtual void ScrollByWhole(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                             nsIScrollbarMediator::ScrollSnapMode aSnap
+                               = nsIScrollbarMediator::DISABLE_SNAP) MOZ_OVERRIDE;
+  virtual void ScrollByLine(nsScrollbarFrame* aScrollbar, int32_t aDirection,
+                            nsIScrollbarMediator::ScrollSnapMode aSnap
+                              = nsIScrollbarMediator::DISABLE_SNAP) MOZ_OVERRIDE;
   virtual void RepeatButtonScroll(nsScrollbarFrame* aScrollbar) MOZ_OVERRIDE;
   virtual void ThumbMoved(nsScrollbarFrame* aScrollbar,
                           nscoord aOldPos,
                           nscoord aNewPos) MOZ_OVERRIDE;
+  virtual void ScrollbarReleased(nsScrollbarFrame* aScrollbar) MOZ_OVERRIDE {}
   virtual void VisibilityChanged(bool aVisible) MOZ_OVERRIDE { Invalidate(); }
   virtual nsIFrame* GetScrollbarBox(bool aVertical) MOZ_OVERRIDE {
     ScrollParts parts = GetScrollParts();