--- a/layout/base/FrameLayerBuilder.cpp
+++ b/layout/base/FrameLayerBuilder.cpp
@@ -3015,29 +3015,34 @@ void ContainerState::FinishPaintedLayerD
       data->mVerticalPanRegion.GetBounds(),
       mContainerReferenceFrame,
       containingPaintedLayerData->mReferenceFrame,
       &containingPaintedLayerData->mVerticalPanRegion,
       &containingPaintedLayerData->mDispatchToContentHitRegion);
 
   } else {
     EventRegions regions;
-    regions.mHitRegion = ScaleRegionToOutsidePixels(data->mHitRegion);
-    regions.mNoActionRegion = ScaleRegionToOutsidePixels(data->mNoActionRegion);
-    regions.mHorizontalPanRegion = ScaleRegionToOutsidePixels(data->mHorizontalPanRegion);
-    regions.mVerticalPanRegion = ScaleRegionToOutsidePixels(data->mVerticalPanRegion);
+    regions.mHitRegion =
+      data->mHitRegion.ToOutsidePixels(mAppUnitsPerDevPixel);
+    regions.mNoActionRegion =
+      data->mNoActionRegion.ToOutsidePixels(mAppUnitsPerDevPixel);
+    regions.mHorizontalPanRegion =
+      data->mHorizontalPanRegion.ToOutsidePixels(mAppUnitsPerDevPixel);
+    regions.mVerticalPanRegion =
+      data->mVerticalPanRegion.ToOutsidePixels(mAppUnitsPerDevPixel);
 
     // Points whose hit-region status we're not sure about need to be dispatched
     // to the content thread. If a point is in both maybeHitRegion and hitRegion
     // then it's not a "maybe" any more, and doesn't go into the dispatch-to-
     // content region.
-    nsIntRegion maybeHitRegion = ScaleRegionToOutsidePixels(data->mMaybeHitRegion);
+    nsIntRegion maybeHitRegion =
+      data->mMaybeHitRegion.ToOutsidePixels(mAppUnitsPerDevPixel);
     regions.mDispatchToContentHitRegion.Sub(maybeHitRegion, regions.mHitRegion);
     regions.mDispatchToContentHitRegion.OrWith(
-        ScaleRegionToOutsidePixels(data->mDispatchToContentHitRegion));
+        data->mDispatchToContentHitRegion.ToOutsidePixels(mAppUnitsPerDevPixel));
     regions.mHitRegion.OrWith(maybeHitRegion);
 
     Matrix mat = layer->GetBaseTransform().As2D();
     mat.Invert();
     regions.ApplyTranslationAndScale(mat._31, mat._32, mat._11, mat._22);
 
     layer->SetEventRegions(regions);
   }