diff --git a/gfx/layers/apz/public/APZPublicUtils.h b/gfx/layers/apz/public/APZPublicUtils.h
index e3de5d0279d4..272422bb71e0 100644
--- a/gfx/layers/apz/public/APZPublicUtils.h
+++ b/gfx/layers/apz/public/APZPublicUtils.h
@@ -12,6 +12,7 @@
 
 #include <stdint.h>  // for uint32_t
 #include <type_traits>
+#include <utility>
 #include "gfxTypes.h"
 #include "FrameMetrics.h"
 #include "LayersTypes.h"
@@ -73,6 +74,15 @@ void InitializeGlobalState();
 const ScreenMargin CalculatePendingDisplayPort(
     const FrameMetrics& aFrameMetrics, const ParentLayerPoint& aVelocity);
 
+/**
+ * This computes the min/max values to use for the mousewheel animation
+ * duration. Normally this just comes from prefs but we are doing a gradual
+ * migration of users from old values to new values so this encapsulates some
+ * of that behaviour. Values are in milliseconds, same as the
+ * general.smoothScroll.mouseWheel.duration* prefs.
+ */
+std::pair<int32_t, int32_t> GetMouseWheelAnimationDurations();
+
 }  // namespace apz
 
 }  // namespace layers
diff --git a/gfx/layers/apz/src/APZPublicUtils.cpp b/gfx/layers/apz/src/APZPublicUtils.cpp
index 645435b947aa..0ed9b377b600 100644
--- a/gfx/layers/apz/src/APZPublicUtils.cpp
+++ b/gfx/layers/apz/src/APZPublicUtils.cpp
@@ -7,6 +7,7 @@
 #include "mozilla/layers/APZPublicUtils.h"
 
 #include "AsyncPanZoomController.h"
+#include "mozilla/StaticPrefs_general.h"
 
 namespace mozilla {
 namespace layers {
@@ -24,6 +25,33 @@ namespace apz {
                                                              aVelocity);
 }
 
+/*static*/ std::pair<int32_t, int32_t> GetMouseWheelAnimationDurations() {
+  // Special code for migrating users from old values to new values over
+  // a period of time. The old values are defaults prior to bug 1660933, which
+  // we hard-code here. The user's migration percentage is stored in the
+  // migration pref. If the migration percentage is zero, the user gets the old
+  // values, and at a 100 percentage the user gets the new values. Linear
+  // interpolation in between. We can control the speed of migration by
+  // increasing the percentage value over time (e.g. by increasing the min
+  // bound on the clamped migration value). Once it reaches 100 the migration
+  // code can be removed.
+
+  int32_t minMS = StaticPrefs::general_smoothScroll_mouseWheel_durationMinMS();
+  int32_t maxMS = StaticPrefs::general_smoothScroll_mouseWheel_durationMaxMS();
+
+  const int32_t oldMin = 200;
+  const int32_t oldMax = 400;
+
+  int32_t migration =
+      StaticPrefs::general_smoothScroll_mouseWheel_migrationPercent();
+  migration = clamped(migration, 0, 100);
+
+  minMS = ((oldMin * (100 - migration)) + (minMS * migration)) / 100;
+  maxMS = ((oldMax * (100 - migration)) + (maxMS * migration)) / 100;
+
+  return std::make_pair(minMS, maxMS);
+}
+
 }  // namespace apz
 }  // namespace layers
 }  // namespace mozilla
diff --git a/gfx/layers/apz/src/WheelScrollAnimation.cpp b/gfx/layers/apz/src/WheelScrollAnimation.cpp
index 9eefcee5eebe..d00004d12700 100644
--- a/gfx/layers/apz/src/WheelScrollAnimation.cpp
+++ b/gfx/layers/apz/src/WheelScrollAnimation.cpp
@@ -5,11 +5,13 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "WheelScrollAnimation.h"
-#include "ScrollAnimationBezierPhysics.h"
 
+#include <tuple>
 #include "AsyncPanZoomController.h"
 #include "mozilla/StaticPrefs_general.h"
+#include "mozilla/layers/APZPublicUtils.h"
 #include "nsPoint.h"
+#include "ScrollAnimationBezierPhysics.h"
 
 namespace mozilla {
 namespace layers {
@@ -33,12 +35,9 @@ static ScrollAnimationBezierPhysicsSettings SettingsForDeltaType(
                       0, maxMS);
       break;
     case ScrollWheelInput::SCROLLDELTA_LINE:
-      maxMS =
-          clamped(StaticPrefs::general_smoothScroll_mouseWheel_durationMaxMS(),
-                  0, 10000);
-      minMS =
-          clamped(StaticPrefs::general_smoothScroll_mouseWheel_durationMinMS(),
-                  0, maxMS);
+      std::tie(minMS, maxMS) = apz::GetMouseWheelAnimationDurations();
+      maxMS = clamped(maxMS, 0, 10000);
+      minMS = clamped(minMS, 0, maxMS);
       break;
   }
 
diff --git a/layout/generic/nsGfxScrollFrame.cpp b/layout/generic/nsGfxScrollFrame.cpp
index 0bc62e99ed3f..3a4fbae38c8a 100644
--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -78,6 +78,7 @@
 #include "ViewportFrame.h"
 #include "mozilla/gfx/gfxVars.h"
 #include "mozilla/layers/APZCCallbackHelper.h"
+#include "mozilla/layers/APZPublicUtils.h"
 #include "mozilla/layers/AxisPhysicsModel.h"
 #include "mozilla/layers/AxisPhysicsMSDModel.h"
 #include "mozilla/layers/LayerTransactionChild.h"
@@ -89,6 +90,7 @@
 #include <algorithm>
 #include <cstdlib>  // for std::abs(int/long)
 #include <cmath>    // for std::abs(float/double)
+#include <tuple>    // for std::tie
 
 static mozilla::LazyLogModule sApzPaintSkipLog("apz.paintskip");
 #define PAINT_SKIP_LOG(...) \
@@ -2119,6 +2121,10 @@ ComputeBezierAnimationSettingsForOrigin(ScrollOrigin aOrigin) {
     minMS = Preferences::GetInt(prefMin.get(), kDefaultMinMS);
     maxMS = Preferences::GetInt(prefMax.get(), kDefaultMaxMS);
 
+    if (aOrigin == ScrollOrigin::MouseWheel) {
+      std::tie(minMS, maxMS) = layers::apz::GetMouseWheelAnimationDurations();
+    }
+
     static const int32_t kSmoothScrollMaxAllowedAnimationDurationMS = 10000;
     maxMS = clamped(maxMS, 0, kSmoothScrollMaxAllowedAnimationDurationMS);
     minMS = clamped(minMS, 0, maxMS);