--- a/gfx/thebes/gfxPrefs.h
+++ b/gfx/thebes/gfxPrefs.h
@@ -549,16 +549,18 @@ 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.event-regions.enabled",          LayoutEventRegionsEnabledDoNotUseDirectly, bool, false);
   DECL_GFX_PREF(Once, "layout.frame_rate",                     LayoutFrameRate, int32_t, -1);
   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);
   DECL_GFX_PREF(Live, "layout.smaller-painted-layers",         LayoutSmallerPaintedLayers, bool, false);
 
   DECL_GFX_PREF(Once, "media.hardware-video-decoding.force-enabled",
                                                                HardwareVideoDecodingForceEnabled, bool, false);
 #ifdef XP_WIN
   DECL_GFX_PREF(Live, "media.windows-media-foundation.allow-d3d11-dxva", PDMWMFAllowD3D11, bool, true);
   DECL_GFX_PREF(Live, "media.windows-media-foundation.max-dxva-videos", PDMWMFMaxDXVAVideos, uint32_t, 8);
   DECL_GFX_PREF(Live, "media.wmf.low-latency.enabled", PDMWMFLowLatencyEnabled, bool, false);

--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -3095,17 +3095,18 @@ ScrollFrameHelper::AppendScrollPartsTo(n
                    : aDirtyRect;
     nsDisplayListBuilder::AutoBuildingDisplayList
       buildingForChild(aBuilder, scrollParts[i],
                        dirty + mOuter->GetOffsetTo(scrollParts[i]), true);
 
     // Always create layers for overlay scrollbars so that we don't create a
     // giant layer covering the whole scrollport if both scrollbars are visible.
     bool isOverlayScrollbar = (flags != 0) && overlayScrollbars;
-    bool createLayer = aCreateLayer || isOverlayScrollbar;
+    bool createLayer = aCreateLayer || isOverlayScrollbar ||
+        gfxPrefs::AlwaysLayerizeScrollbarTrackTestOnly();
 
     nsDisplayListBuilder::AutoCurrentScrollbarInfoSetter
       infoSetter(aBuilder, scrollTargetId, flags, createLayer);
     nsDisplayListCollection partList;
     mOuter->BuildDisplayListForChild(
       aBuilder, scrollParts[i], dirty, partList,
       nsIFrame::DISPLAY_CHILD_FORCE_STACKING_CONTEXT);
 

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -712,16 +712,18 @@ pref("apz.y_stationary_size_multiplier",
 pref("gfx.hidpi.enabled", 2);
 #endif
 
 #if !defined(MOZ_WIDGET_GONK) && !defined(MOZ_WIDGET_ANDROID)
 // Use containerless scrolling for now on desktop.
 pref("layout.scroll.root-frame-containers", false);
 #endif
 
+pref("layout.scrollbars.always-layerize-track", false);
+
 // Whether to enable LayerScope tool and default listening port
 pref("gfx.layerscope.enabled", false);
 pref("gfx.layerscope.port", 23456);
 
 // Log severe performance warnings to the error console and profiles.
 // This should be use to quickly find which slow paths are used by test cases.
 pref("gfx.perf-warnings.enabled", false);