diff --git a/gfx/layers/apz/src/APZCTreeManager.cpp b/gfx/layers/apz/src/APZCTreeManager.cpp
index c1d214e92857..447de4d30ed8 100644
--- a/gfx/layers/apz/src/APZCTreeManager.cpp
+++ b/gfx/layers/apz/src/APZCTreeManager.cpp
@@ -1315,8 +1315,8 @@ APZCTreeManager::GetAPZCAtPoint(AsyncPanZoomController* aApzc,
    required can be generated.
  */
 void
-APZCTreeManager::GetInputTransforms(AsyncPanZoomController *aApzc, Matrix4x4& aTransformToApzcOut,
-                                    Matrix4x4& aTransformToGeckoOut)
+APZCTreeManager::GetInputTransforms(const AsyncPanZoomController *aApzc, Matrix4x4& aTransformToApzcOut,
+                                    Matrix4x4& aTransformToGeckoOut) const
 {
   MonitorAutoLock lock(mTreeLock);
 
diff --git a/gfx/layers/apz/src/APZCTreeManager.h b/gfx/layers/apz/src/APZCTreeManager.h
index 9e3c0e5242cd..d2d008321bb6 100644
--- a/gfx/layers/apz/src/APZCTreeManager.h
+++ b/gfx/layers/apz/src/APZCTreeManager.h
@@ -361,8 +361,9 @@ public:
   already_AddRefed<AsyncPanZoomController> GetTargetAPZC(const ScrollableLayerGuid& aGuid);
   already_AddRefed<AsyncPanZoomController> GetTargetAPZC(const ScreenPoint& aPoint,
                                                          bool* aOutInOverscrolledApzc);
-  void GetInputTransforms(AsyncPanZoomController *aApzc, gfx::Matrix4x4& aTransformToApzcOut,
-                          gfx::Matrix4x4& aTransformToGeckoOut);
+  void GetInputTransforms(const AsyncPanZoomController *aApzc,
+                          gfx::Matrix4x4& aTransformToApzcOut,
+                          gfx::Matrix4x4& aTransformToGeckoOut) const;
 private:
   /* Helpers */
   AsyncPanZoomController* FindTargetAPZC(AsyncPanZoomController* aApzc, FrameMetrics::ViewID aScrollId);
@@ -417,7 +418,7 @@ private:
    * is considered part of the APZC tree management state.
    * Finally, the lock needs to be held when accessing mOverscrollHandoffChain.
    * IMPORTANT: See the note about lock ordering at the top of this file. */
-  mozilla::Monitor mTreeLock;
+  mutable mozilla::Monitor mTreeLock;
   nsRefPtr<AsyncPanZoomController> mRootApzc;
   /* This tracks the APZC that should receive all inputs for the current input event block.
    * This allows touch points to move outside the thing they started on, but still have the
diff --git a/gfx/layers/apz/src/AsyncPanZoomController.cpp b/gfx/layers/apz/src/AsyncPanZoomController.cpp
index 4e3e2fa6daef..cf96e314d439 100644
--- a/gfx/layers/apz/src/AsyncPanZoomController.cpp
+++ b/gfx/layers/apz/src/AsyncPanZoomController.cpp
@@ -927,7 +927,7 @@ AsyncPanZoomController::Destroy()
 }
 
 bool
-AsyncPanZoomController::IsDestroyed()
+AsyncPanZoomController::IsDestroyed() const
 {
   return mTreeManager == nullptr;
 }
@@ -1694,7 +1694,7 @@ nsEventStatus AsyncPanZoomController::OnCancelTap(const TapGestureInput& aEvent)
   return nsEventStatus_eIgnore;
 }
 
-float AsyncPanZoomController::PanDistance() {
+float AsyncPanZoomController::PanDistance() const {
   ReentrantMonitorAutoEnter lock(mMonitor);
   return NS_hypot(mX.PanDistance(), mY.PanDistance());
 }
@@ -2465,7 +2465,7 @@ void AsyncPanZoomController::SampleContentTransformForFrame(ViewTransform* aOutT
   }
 }
 
-ViewTransform AsyncPanZoomController::GetCurrentAsyncTransform() {
+ViewTransform AsyncPanZoomController::GetCurrentAsyncTransform() const {
   ReentrantMonitorAutoEnter lock(mMonitor);
 
   CSSPoint lastPaintScrollOffset;
@@ -2503,14 +2503,14 @@ ViewTransform AsyncPanZoomController::GetCurrentAsyncTransform() {
   return ViewTransform(scale, -translation);
 }
 
-Matrix4x4 AsyncPanZoomController::GetNontransientAsyncTransform() {
+Matrix4x4 AsyncPanZoomController::GetNontransientAsyncTransform() const {
   ReentrantMonitorAutoEnter lock(mMonitor);
   return Matrix4x4().Scale(mLastContentPaintMetrics.mResolution.scale,
                            mLastContentPaintMetrics.mResolution.scale,
                            1.0f);
 }
 
-Matrix4x4 AsyncPanZoomController::GetTransformToLastDispatchedPaint() {
+Matrix4x4 AsyncPanZoomController::GetTransformToLastDispatchedPaint() const {
   ReentrantMonitorAutoEnter lock(mMonitor);
 
   // Technically we should be taking the scroll delta in the coordinate space
diff --git a/gfx/layers/apz/src/AsyncPanZoomController.h b/gfx/layers/apz/src/AsyncPanZoomController.h
index cb34c2941ed6..ff2de9964b5b 100644
--- a/gfx/layers/apz/src/AsyncPanZoomController.h
+++ b/gfx/layers/apz/src/AsyncPanZoomController.h
@@ -212,7 +212,7 @@ public:
   /**
    * Returns true if Destroy() has already been called on this APZC instance.
    */
-  bool IsDestroyed();
+  bool IsDestroyed() const;
 
   /**
    * Returns the incremental transformation corresponding to the async pan/zoom
@@ -220,14 +220,14 @@ public:
    * existing transform, it will make the layer appear with the desired pan/zoom
    * amount.
    */
-  ViewTransform GetCurrentAsyncTransform();
+  ViewTransform GetCurrentAsyncTransform() const;
 
   /**
    * Returns the part of the async transform that will remain once Gecko does a
    * repaint at the desired metrics. That is, in the steady state:
    * Matrix4x4(GetCurrentAsyncTransform()) === GetNontransientAsyncTransform()
    */
-  Matrix4x4 GetNontransientAsyncTransform();
+  Matrix4x4 GetNontransientAsyncTransform() const;
 
   /**
    * Returns the transform to take something from the coordinate space of the
@@ -236,7 +236,7 @@ public:
    * processed, this is needed to transform input events properly into a space
    * gecko will understand.
    */
-  Matrix4x4 GetTransformToLastDispatchedPaint();
+  Matrix4x4 GetTransformToLastDispatchedPaint() const;
 
   /**
    * Recalculates the displayport. Ideally, this should paint an area bigger
@@ -464,7 +464,7 @@ protected:
    * current touch (this only makes sense if a touch is currently happening and
    * OnTouchMove() is being invoked).
    */
-  float PanDistance();
+  float PanDistance() const;
 
   /**
    * Gets a vector of the velocities of each axis.
diff --git a/gfx/layers/apz/src/Axis.cpp b/gfx/layers/apz/src/Axis.cpp
index bd25364a5b87..ba1a00976bad 100644
--- a/gfx/layers/apz/src/Axis.cpp
+++ b/gfx/layers/apz/src/Axis.cpp
@@ -207,11 +207,11 @@ void Axis::ClearOverscroll() {
   mOverscroll = 0;
 }
 
-float Axis::PanDistance() {
+float Axis::PanDistance() const {
   return fabsf((mPos - mStartPos).value);
 }
 
-float Axis::PanDistance(ScreenCoord aPos) {
+float Axis::PanDistance(ScreenCoord aPos) const {
   return fabsf((aPos - mStartPos).value);
 }
 
diff --git a/gfx/layers/apz/src/Axis.h b/gfx/layers/apz/src/Axis.h
index 1068630413b2..f825ac038975 100644
--- a/gfx/layers/apz/src/Axis.h
+++ b/gfx/layers/apz/src/Axis.h
@@ -123,13 +123,13 @@ public:
    * startTouch() and the current touch from the last
    * updateWithTouchAtDevicePoint().
    */
-  float PanDistance();
+  float PanDistance() const;
 
   /**
    * Gets the distance between the starting position of the touch supplied in
    * startTouch() and the supplied position.
    */
-  float PanDistance(ScreenCoord aPos);
+  float PanDistance(ScreenCoord aPos) const;
 
   /**
    * Applies friction during a fling, or cancels the fling if the velocity is