--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -3003,38 +3003,16 @@ MaxZIndexInList(nsDisplayList* aList, ns
 {
   int32_t maxZIndex = -1;
   for (nsDisplayItem* item = aList->GetBottom(); item; item = item->GetAbove()) {
     maxZIndex = std::max(maxZIndex, item->ZIndex());
   }
   return maxZIndex;
 }
 
-// Finds the max z-index of the items in aList that meet the following conditions
-//   1) have z-index auto or z-index >= 0.
-//   2) aFrame is a proper ancestor of the item's frame.
-// Returns -1 if there is no such item.
-static int32_t
-MaxZIndexInListOfItemsContainedInFrame(nsDisplayList* aList, nsIFrame* aFrame)
-{
-  int32_t maxZIndex = -1;
-  for (nsDisplayItem* item = aList->GetBottom(); item; item = item->GetAbove()) {
-    nsIFrame* itemFrame = item->Frame();
-    // Perspective items return the scroll frame as their Frame(), so consider
-    // their TransformFrame() instead.
-    if (item->GetType() == DisplayItemType::TYPE_PERSPECTIVE) {
-      itemFrame = static_cast<nsDisplayPerspective*>(item)->TransformFrame();
-    }
-    if (nsLayoutUtils::IsProperAncestorFrame(aFrame, itemFrame)) {
-      maxZIndex = std::max(maxZIndex, item->ZIndex());
-    }
-  }
-  return maxZIndex;
-}
-
 template<class T>
 static void
 AppendInternalItemToTop(const nsDisplayListSet& aLists,
                         T* aItem,
                         int32_t aZIndex)
 {
   if (aZIndex >= 0) {
     aItem->SetOverrideZIndex(aZIndex);
@@ -3705,18 +3683,16 @@ ScrollFrameHelper::BuildDisplayList(nsDi
   if (mWillBuildScrollableLayer && aBuilder->IsPaintingToWindow()) {
     aBuilder->ForceLayerForScrollParent();
   }
 
   if (couldBuildLayer) {
     // Make sure that APZ will dispatch events back to content so we can create
     // a displayport for this frame. We'll add the item later on.
     if (!mWillBuildScrollableLayer) {
-      int32_t zIndex =
-        MaxZIndexInListOfItemsContainedInFrame(scrolledContent.PositionedDescendants(), mOuter);
       if (aBuilder->BuildCompositorHitTestInfo()) {
         CompositorHitTestInfo info = CompositorHitTestInfo::eVisibleToHitTest
                                    | CompositorHitTestInfo::eDispatchToContent;
         // If the scroll frame has non-default overscroll-behavior, instruct
         // APZ to require a target confirmation before processing events that
         // hit this scroll frame (that is, to drop the events if a confirmation
         // does not arrive within the timeout period). Otherwise, APZ's
         // fallback behaviour of scrolling the enclosing scroll frame would
@@ -3724,23 +3700,23 @@ ScrollFrameHelper::BuildDisplayList(nsDi
         ScrollbarStyles scrollbarStyles = GetScrollbarStylesFromFrame();
         if (scrollbarStyles.mOverscrollBehaviorX != StyleOverscrollBehavior::Auto ||
             scrollbarStyles.mOverscrollBehaviorY != StyleOverscrollBehavior::Auto) {
           info |= CompositorHitTestInfo::eRequiresTargetConfirmation;
         }
         nsDisplayCompositorHitTestInfo* hitInfo =
             MakeDisplayItem<nsDisplayCompositorHitTestInfo>(aBuilder, mScrolledFrame, info, 1,
                 Some(mScrollPort + aBuilder->ToReferenceFrame(mOuter)));
-        AppendInternalItemToTop(scrolledContent, hitInfo, zIndex);
+        AppendInternalItemToTop(scrolledContent, hitInfo, INT32_MAX);
       }
       if (aBuilder->IsBuildingLayerEventRegions()) {
         nsDisplayLayerEventRegions* inactiveRegionItem =
             MakeDisplayItem<nsDisplayLayerEventRegions>(aBuilder, mScrolledFrame, 1);
         inactiveRegionItem->AddInactiveScrollPort(mScrolledFrame, mScrollPort + aBuilder->ToReferenceFrame(mOuter));
-        AppendInternalItemToTop(scrolledContent, inactiveRegionItem, zIndex);
+        AppendInternalItemToTop(scrolledContent, inactiveRegionItem, INT32_MAX);
       }
     }
 
     if (aBuilder->ShouldBuildScrollInfoItemsForHoisting()) {
       aBuilder->AppendNewScrollInfoItemForHoisting(
         MakeDisplayItem<nsDisplayScrollInfoLayer>(aBuilder, mScrolledFrame,
                                                 mOuter));
     }