--- a/dom/events/EventListenerManager.cpp
+++ b/dom/events/EventListenerManager.cpp
@@ -456,17 +456,17 @@ EventListenerManager::ProcessApzAwareEve
   if (!doc) {
     if (nsCOMPtr<DOMEventTargetHelper> helper = do_QueryInterface(mTarget)) {
       if (nsPIDOMWindowInner* window = helper->GetOwner()) {
         doc = window->GetExtantDoc();
       }
     }
   }
 
-  if (doc && nsDisplayListBuilder::LayerEventRegionsEnabled()) {
+  if (doc && gfxPlatform::AsyncPanZoomEnabled()) {
     nsIPresShell* ps = doc->GetShell();
     if (ps) {
       nsIFrame* f = ps->GetRootFrame();
       if (f) {
         f->SchedulePaint();
       }
     }
   }

--- a/gfx/thebes/gfxPrefs.h
+++ b/gfx/thebes/gfxPrefs.h
@@ -677,17 +677,16 @@ private:
   DECL_GFX_PREF(Live, "layout.display-list.dump",              LayoutDumpDisplayList, bool, false);
   DECL_GFX_PREF(Live, "layout.display-list.dump-content",      LayoutDumpDisplayListContent, bool, false);
   DECL_GFX_PREF(Live, "layout.display-list.dump-parent",       LayoutDumpDisplayListParent, bool, false);
   DECL_GFX_PREF(Live, "layout.display-list.show-rebuild-area", LayoutDisplayListShowArea, bool, false);
 
   DECL_GFX_PREF(Once, "layout.simple-event-region-items",      SimpleEventRegionItems, bool, true);
   DECL_GFX_PREF(Once, "layout.less-event-region-items",        LessEventRegionItems, bool, true);
 
-  DECL_GFX_PREF(Live, "layout.event-regions.enabled",          LayoutEventRegionsEnabledDoNotUseDirectly, bool, false);
   DECL_GFX_PREF(Once, "layout.frame_rate",                     LayoutFrameRate, int32_t, -1);
   DECL_GFX_PREF(Live, "layout.min-active-layer-size",          LayoutMinActiveLayerSize, int, 64);
   DECL_GFX_PREF(Once, "layout.paint_rects_separately",         LayoutPaintRectsSeparately, bool, true);
 
   // This and code dependent on it should be removed once containerless scrolling looks stable.
   DECL_GFX_PREF(Once, "layout.scroll.root-frame-containers",   LayoutUseContainersForRootFrames, bool, true);
   // This pref is to be set by test code only.
   DECL_GFX_PREF(Live, "layout.scrollbars.always-layerize-track", AlwaysLayerizeScrollbarTrackTestOnly, bool, false);

--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -3673,17 +3673,17 @@ nsLayoutUtils::PaintFrame(gfxContext* aR
         }
       }
 
       nsDisplayListBuilder::AutoCurrentScrollParentIdSetter idSetter(&builder, id);
 
       builder.SetVisibleRect(visibleRect);
       builder.SetIsBuilding(true);
       builder.SetAncestorHasApzAwareEventHandler(
-          nsDisplayListBuilder::LayerEventRegionsEnabled() &&
+          gfxPlatform::AsyncPanZoomEnabled() &&
           nsLayoutUtils::HasDocumentLevelListenersForApzAwareEvents(presShell));
 
       DisplayListChecker beforeMergeChecker;
       DisplayListChecker toBeMergedChecker;
       DisplayListChecker afterMergeChecker;
 
       // Attempt to do a partial build and merge into the existing list.
       // This calls BuildDisplayListForStacking context on a subset of the

--- a/layout/generic/nsSubDocumentFrame.cpp
+++ b/layout/generic/nsSubDocumentFrame.cpp
@@ -492,17 +492,17 @@ nsSubDocumentFrame::BuildDisplayList(nsD
       nsIFrame* rootScrollFrame = presShell->GetRootScrollFrame();
       nsDisplayListBuilder::AutoCurrentScrollParentIdSetter idSetter(
           aBuilder,
           ignoreViewportScrolling && rootScrollFrame && rootScrollFrame->GetContent()
               ? nsLayoutUtils::FindOrCreateIDFor(rootScrollFrame->GetContent())
               : aBuilder->GetCurrentScrollParentId());
 
       bool hasDocumentLevelListenersForApzAwareEvents =
-          nsDisplayListBuilder::LayerEventRegionsEnabled() &&
+          gfxPlatform::AsyncPanZoomEnabled() &&
           nsLayoutUtils::HasDocumentLevelListenersForApzAwareEvents(presShell);
 
       aBuilder->SetAncestorHasApzAwareEventHandler(hasDocumentLevelListenersForApzAwareEvents);
       subdocRootFrame->
         BuildDisplayListForStackingContext(aBuilder, &childItems);
     }
 
     if (!aBuilder->IsForEventDelivery()) {

--- a/layout/painting/nsDisplayList.cpp
+++ b/layout/painting/nsDisplayList.cpp
@@ -2297,35 +2297,21 @@ nsDisplayListBuilder::IsBuildingLayerEve
 {
   if (mBuildCompositorHitTestInfo) {
     // If we have webrender hit-testing enabled, then we will build the
     // nsDisplayCompositorHitTestInfo items and use those instead of event
     // regions, so we don't need to build the event regions.
     return false;
   }
   if (IsPaintingToWindow()) {
-    // Note: this function and LayerEventRegionsEnabled are the only places
-    // that get to query LayoutEventRegionsEnabled 'directly' - other code
-    // should call this function.
-    return gfxPrefs::LayoutEventRegionsEnabledDoNotUseDirectly() ||
-           mAsyncPanZoomEnabled;
+    return mAsyncPanZoomEnabled;
   }
   return false;
 }
 
-/* static */ bool
-nsDisplayListBuilder::LayerEventRegionsEnabled()
-{
-  // Note: this function and IsBuildingLayerEventRegions are the only places
-  // that get to query LayoutEventRegionsEnabled 'directly' - other code
-  // should call this function.
-  return gfxPrefs::LayoutEventRegionsEnabledDoNotUseDirectly() ||
-         gfxPlatform::AsyncPanZoomEnabled();
-}
-
 void nsDisplayListSet::MoveTo(const nsDisplayListSet& aDestination) const
 {
   aDestination.BorderBackground()->AppendToTop(BorderBackground());
   aDestination.BlockBorderBackgrounds()->AppendToTop(BlockBorderBackgrounds());
   aDestination.Floats()->AppendToTop(Floats());
   aDestination.Content()->AppendToTop(Content());
   aDestination.PositionedDescendants()->AppendToTop(PositionedDescendants());
   aDestination.Outlines()->AppendToTop(Outlines());

--- a/layout/painting/nsDisplayList.h
+++ b/layout/painting/nsDisplayList.h
@@ -751,17 +751,16 @@ public:
    * needed, and adds it to the top of |aList|. If |aBuildNew| is true, the
    * previous hit test info will not be reused.
    */
   void BuildCompositorHitTestInfoIfNeeded(nsIFrame* aFrame,
                                           nsDisplayList* aList,
                                           const bool aBuildNew);
 
   bool IsBuildingLayerEventRegions();
-  static bool LayerEventRegionsEnabled();
   bool IsInsidePointerEventsNoneDoc()
   {
     return CurrentPresShellState()->mInsidePointerEventsNoneDoc;
   }
 
   bool GetAncestorHasApzAwareEventHandler() const { return mAncestorHasApzAwareEventHandler; }
   void SetAncestorHasApzAwareEventHandler(bool aValue)
   {

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -600,19 +600,16 @@ pref("media.cubeb.sandbox", false);
 pref("media.webaudio.audiocontextoptions-samplerate.enabled", true);
 
 // Weather we allow AMD switchable graphics
 pref("layers.amd-switchable-gfx.enabled", true);
 
 // Whether to use async panning and zooming
 pref("layers.async-pan-zoom.enabled", true);
 
-// Whether to enable event region building during painting
-pref("layout.event-regions.enabled", false);
-
 // Whether to enable arbitrary layer geometry for OpenGL compositor
 pref("layers.geometry.opengl.enabled", true);
 
 // Whether to enable arbitrary layer geometry for Basic compositor
 pref("layers.geometry.basic.enabled", true);
 
 // Whether to enable arbitrary layer geometry for DirectX compositor
 pref("layers.geometry.d3d11.enabled", true);