--- a/layout/base/nsPresArena.cpp
+++ b/layout/base/nsPresArena.cpp
@@ -8,17 +8,17 @@
 /* arena allocation for the frame tree and closely-related objects */
 
 #include "nsPresArena.h"
 
 #include "mozilla/Poison.h"
 #include "nsDebug.h"
 #include "nsArenaMemoryStats.h"
 #include "nsPrintfCString.h"
-#include "nsStyleContext.h"
+#include "GeckoStyleContext.h"
 #include "FrameLayerBuilder.h"
 #include "mozilla/ArrayUtils.h"
 
 #include <inttypes.h>
 
 using namespace mozilla;
 
 nsPresArena::nsPresArena()
@@ -203,17 +203,17 @@ nsPresArena::AddSizeOfExcludingThis(mozi
 #undef FRAME_ID
 #undef ABSTRACT_FRAME_ID
       case eArenaObjectID_nsLineBox:
         p = &aArenaStats->mLineBoxes;
         break;
       case eArenaObjectID_nsRuleNode:
         p = &aArenaStats->mRuleNodes;
         break;
-      case eArenaObjectID_nsStyleContext:
+      case eArenaObjectID_GeckoStyleContext:
         p = &aArenaStats->mStyleContexts;
         break;
 #define STYLE_STRUCT(name_, checkdata_cb_)      \
         case eArenaObjectID_nsStyle##name_:
 #include "nsStyleStructList.h"
 #undef STYLE_STRUCT
         p = &aArenaStats->mStyleStructs;
         break;

--- a/layout/base/nsPresArenaObjectList.h
+++ b/layout/base/nsPresArenaObjectList.h
@@ -42,17 +42,17 @@
 //
 // Files including nsPresArenaObjectList.h can either define one or both
 // of PRES_ARENA_OBJECT_{WITH,WITHOUT}_ARENAREFPTR_SUPPORT to capture those
 // classes separately, or PRES_ARENA_OBJECT to capture all nsPresArena-
 // allocated classes.
 
 PRES_ARENA_OBJECT_WITHOUT_ARENAREFPTR_SUPPORT(nsLineBox)
 PRES_ARENA_OBJECT_WITHOUT_ARENAREFPTR_SUPPORT(nsRuleNode)
-PRES_ARENA_OBJECT_WITH_ARENAREFPTR_SUPPORT(nsStyleContext)
+PRES_ARENA_OBJECT_WITH_ARENAREFPTR_SUPPORT(GeckoStyleContext)
 PRES_ARENA_OBJECT_WITHOUT_ARENAREFPTR_SUPPORT(DisplayItemData)
 PRES_ARENA_OBJECT_WITHOUT_ARENAREFPTR_SUPPORT(nsInheritedStyleData)
 PRES_ARENA_OBJECT_WITHOUT_ARENAREFPTR_SUPPORT(nsResetStyleData)
 PRES_ARENA_OBJECT_WITHOUT_ARENAREFPTR_SUPPORT(nsConditionalResetStyleData)
 PRES_ARENA_OBJECT_WITHOUT_ARENAREFPTR_SUPPORT(nsConditionalResetStyleDataEntry)
 PRES_ARENA_OBJECT_WITHOUT_ARENAREFPTR_SUPPORT(nsFrameList)
 PRES_ARENA_OBJECT_WITHOUT_ARENAREFPTR_SUPPORT(CustomCounterStyle)
 PRES_ARENA_OBJECT_WITHOUT_ARENAREFPTR_SUPPORT(DependentBuiltinCounterStyle)

--- a/layout/style/GeckoStyleContext.cpp
+++ b/layout/style/GeckoStyleContext.cpp
@@ -40,12 +40,13 @@ GeckoStyleContext::GeckoStyleContext(nsS
   ApplyStyleFixups(aSkipParentDisplayBasedStyleFixup);
 }
 
 // Overloaded new operator. Initializes the memory to 0 and relies on an arena
 // (which comes from the presShell) to perform the allocation.
 void*
 GeckoStyleContext::operator new(size_t sz, nsPresContext* aPresContext)
 {
+  MOZ_ASSERT(sz == sizeof(GeckoStyleContext));
   // Check the recycle list first.
   return aPresContext->PresShell()->
-    AllocateByObjectID(eArenaObjectID_nsStyleContext, sz);
+    AllocateByObjectID(eArenaObjectID_GeckoStyleContext, sz);
 }

--- a/layout/style/nsStyleContext.cpp
+++ b/layout/style/nsStyleContext.cpp
@@ -1332,17 +1332,17 @@ nsStyleContext::Destroy()
   if (IsGecko()) {
     // Get the pres context.
     RefPtr<nsPresContext> presContext = PresContext();
     // Call our destructor.
     this->AsGecko()->~GeckoStyleContext();
     // Don't let the memory be freed, since it will be recycled
     // instead. Don't call the global operator delete.
     presContext->PresShell()->
-      FreeByObjectID(eArenaObjectID_nsStyleContext, this);
+      FreeByObjectID(eArenaObjectID_GeckoStyleContext, this);
     } else {
       delete static_cast<ServoStyleContext*>(this);
     }
 }
 
 already_AddRefed<nsStyleContext>
 NS_NewStyleContext(nsStyleContext* aParentContext,
                    nsIAtom* aPseudoTag,

--- a/layout/style/nsStyleContext.h
+++ b/layout/style/nsStyleContext.h
@@ -67,17 +67,17 @@ public:
 #endif
   MOZ_DECL_STYLO_CONVERT_METHODS(mozilla::GeckoStyleContext, mozilla::ServoStyleContext);
 
   void Destroy();
 
   // These two methods are for use by ArenaRefPtr.
   static mozilla::ArenaObjectID ArenaObjectID()
   {
-    return mozilla::eArenaObjectID_nsStyleContext;
+    return mozilla::eArenaObjectID_GeckoStyleContext;
   }
   nsIPresShell* Arena();
 
 #ifdef DEBUG
   /**
    * Initializes a cached pref, which is only used in DEBUG code.
    */
   static void Initialize();

--- a/layout/style/nsStyleSet.cpp
+++ b/layout/style/nsStyleSet.cpp
@@ -303,17 +303,17 @@ nsresult
 nsStyleSet::BeginReconstruct()
 {
   NS_ASSERTION(!mInReconstruct, "Unmatched begin/end?");
   NS_ASSERTION(mRuleTree, "Reconstructing before first construction?");
   mInReconstruct = true;
 
   // Clear any ArenaRefPtr-managed style contexts, as we don't want them
   // held on to after the rule tree has been reconstructed.
-  PresContext()->PresShell()->ClearArenaRefPtrs(eArenaObjectID_nsStyleContext);
+  PresContext()->PresShell()->ClearArenaRefPtrs(eArenaObjectID_GeckoStyleContext);
 
   // Clear our cached style contexts for non-inheriting anonymous boxes.
   ClearNonInheritingStyleContexts();
 
 #ifdef DEBUG
   MOZ_ASSERT(!mOldRootNode);
   mOldRootNode = mRuleTree;
 #endif