--- a/layout/style/nsStyleContext.cpp
+++ b/layout/style/nsStyleContext.cpp
@@ -463,18 +463,34 @@ const void* nsStyleContext::StyleData(ns
   if (mSource.IsGeckoRuleNode()) {
     newData = mSource.AsGeckoRuleNode()->GetStyleData(aSID, this, true);
     if (!nsCachedStyleData::IsReset(aSID)) {
       // always cache inherited data on the style context; the rule
       // node set the bit in mBits for us if needed.
       mCachedInheritedData.mStyleStructs[aSID] = const_cast<void*>(newData);
     }
   } else {
+    newData = StyleStructFromServoComputedValues(aSID);
+
+    // perform any remaining main thread work on the struct
+    switch (aSID) {
+#define STYLE_STRUCT(name_, checkdata_cb_)                                    \
+      case eStyleStruct_##name_: {                                            \
+        auto data = static_cast<const nsStyle##name_*>(newData);              \
+        const_cast<nsStyle##name_*>(data)->FinishStyle(PresContext());        \
+        break;                                                                \
+      }
+#include "nsStyleStructList.h"
+#undef STYLE_STRUCT
+      default:
+        MOZ_ASSERT_UNREACHABLE("unexpected nsStyleStructID value");
+        break;
+    }
+
     // The Servo-backed StyleContextSource owns the struct.
-    newData = StyleStructFromServoComputedValues(aSID);
     AddStyleBit(nsCachedStyleData::GetBitForSID(aSID));
 
     // XXXbholley: Unconditionally caching reset structs here defeats the memory
     // optimization where we lazily allocate mCachedResetData, so that we can avoid
     // performing an FFI call each time we want to get the style structs. We should
     // measure the tradeoffs at some point. If the FFI overhead is low and the memory
     // win significant, we should consider _always_ grabbing the struct over FFI, and
     // potentially giving mCachedInheritedData the same treatment.

--- a/layout/style/nsStyleContext.h
+++ b/layout/style/nsStyleContext.h
@@ -668,16 +668,18 @@ private:
           newData = mParent->DoGetStyle##name_<true>();                 \
           NS_WARNING_ASSERTION(                                         \
             newData == Servo_GetStyle##name_(mSource.AsServoComputedValues()), \
             "bad newData");                                             \
         } else {                                                        \
           newData =                                                     \
             Servo_GetStyle##name_(mSource.AsServoComputedValues());     \
         }                                                               \
+        /* perform any remaining main thread work on the struct */      \
+        const_cast<nsStyle##name_*>(newData)->FinishStyle(PresContext());\
         /* the Servo-backed StyleContextSource owns the struct */       \
         AddStyleBit(NS_STYLE_INHERIT_BIT(name_));                       \
       }                                                                 \
       /* always cache inherited data on the style context; the rule */  \
       /* node set the bit in mBits for us if needed. */                 \
       mCachedInheritedData.mStyleStructs[eStyleStruct_##name_] =        \
         const_cast<nsStyle##name_ *>(newData);                          \
       return newData;                                                   \
@@ -696,16 +698,18 @@ private:
       AUTO_CHECK_DEPENDENCY(eStyleStruct_##name_);                      \
       const nsStyle##name_ * newData;                                   \
       if (mSource.IsGeckoRuleNode()) {                                  \
         newData = mSource.AsGeckoRuleNode()->                           \
           GetStyle##name_<aComputeData>(this);                          \
       } else {                                                          \
         newData =                                                       \
           Servo_GetStyle##name_(mSource.AsServoComputedValues());       \
+        /* perform any remaining main thread work on the struct */      \
+        const_cast<nsStyle##name_*>(newData)->FinishStyle(PresContext());\
         /* The Servo-backed StyleContextSource owns the struct.         \
          *                                                              \
          * XXXbholley: Unconditionally caching reset structs here       \
          * defeats the memory optimization where we lazily allocate     \
          * mCachedResetData, so that we can avoid performing an FFI     \
          * call each time we want to get the style structs. We should   \
          * measure the tradeoffs at some point. If the FFI overhead is  \
          * low and the memory win significant, we should consider       \

--- a/layout/style/nsStyleStruct.h
+++ b/layout/style/nsStyleStruct.h
@@ -161,16 +161,17 @@ struct Position {
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleFont
 {
   nsStyleFont(const nsFont& aFont, StyleStructContext aContext);
   nsStyleFont(const nsStyleFont& aStyleFont);
   explicit nsStyleFont(StyleStructContext aContext);
   ~nsStyleFont() {
     MOZ_COUNT_DTOR(nsStyleFont);
   }
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   nsChangeHint CalcDifference(const nsStyleFont& aNewData) const;
   static nsChangeHint MaxDifference() {
     return NS_STYLE_HINT_REFLOW |
            nsChangeHint_NeutralChange;
   }
   static nsChangeHint DifferenceAlwaysHandledForDescendants() {
     // CalcDifference never returns the reflow hints that are sometimes
@@ -544,16 +545,17 @@ private:
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleColor
 {
   explicit nsStyleColor(StyleStructContext aContext);
   nsStyleColor(const nsStyleColor& aOther);
   ~nsStyleColor() {
     MOZ_COUNT_DTOR(nsStyleColor);
   }
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   nscolor CalcComplexColor(const mozilla::StyleComplexColor& aColor) const {
     return mozilla::LinearBlendColors(aColor.mColor, mColor,
                                       aColor.mForegroundRatio);
   }
 
   nsChangeHint CalcDifference(const nsStyleColor& aNewData) const;
   static nsChangeHint MaxDifference() {
@@ -899,16 +901,17 @@ struct nsStyleImageLayers {
     NS_ASSERTION((count_) > 0 && (count_) <= (start_) + 1, "Invalid layer range!"); \
     for (uint32_t var_ = (start_) + 1; var_-- != (uint32_t)((start_) + 1 - (count_)); )
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleBackground {
   explicit nsStyleBackground(StyleStructContext aContext);
   nsStyleBackground(const nsStyleBackground& aOther);
   ~nsStyleBackground();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleBackground* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleBackground, sz);
   }
   void Destroy(nsPresContext* aContext);
 
@@ -951,16 +954,17 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsSt
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleMargin
 {
   explicit nsStyleMargin(StyleStructContext aContext);
   nsStyleMargin(const nsStyleMargin& aMargin);
   ~nsStyleMargin() {
     MOZ_COUNT_DTOR(nsStyleMargin);
   }
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleMargin* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleMargin, sz);
   }
   void Destroy(nsPresContext* aContext);
 
@@ -998,16 +1002,17 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsSt
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStylePadding
 {
   explicit nsStylePadding(StyleStructContext aContext);
   nsStylePadding(const nsStylePadding& aPadding);
   ~nsStylePadding() {
     MOZ_COUNT_DTOR(nsStylePadding);
   }
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStylePadding* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStylePadding, sz);
   }
   void Destroy(nsPresContext* aContext);
 
@@ -1205,16 +1210,17 @@ static bool IsVisibleBorderStyle(uint8_t
           aStyle != NS_STYLE_BORDER_STYLE_HIDDEN);
 }
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleBorder
 {
   explicit nsStyleBorder(StyleStructContext aContext);
   nsStyleBorder(const nsStyleBorder& aBorder);
   ~nsStyleBorder();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleBorder* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleBorder, sz);
   }
   void Destroy(nsPresContext* aContext);
 
@@ -1434,16 +1440,17 @@ ASSERT_BORDER_COLOR_FIELD(Left);
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleOutline
 {
   explicit nsStyleOutline(StyleStructContext aContext);
   nsStyleOutline(const nsStyleOutline& aOutline);
   ~nsStyleOutline() {
     MOZ_COUNT_DTOR(nsStyleOutline);
   }
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleOutline* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleOutline, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStyleOutline();
@@ -1507,16 +1514,17 @@ private:
   ~nsStyleQuoteValues() {}
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleList
 {
   explicit nsStyleList(StyleStructContext aContext);
   nsStyleList(const nsStyleList& aStyleList);
   ~nsStyleList();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleList* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleList, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStyleList();
@@ -1736,16 +1744,17 @@ struct nsStyleGridTemplate
   }
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStylePosition
 {
   explicit nsStylePosition(StyleStructContext aContext);
   nsStylePosition(const nsStylePosition& aOther);
   ~nsStylePosition();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStylePosition* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStylePosition, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStylePosition();
@@ -1972,16 +1981,17 @@ struct nsStyleTextOverflow
   bool mLogicalDirections;  // true when only one value was specified
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleTextReset
 {
   explicit nsStyleTextReset(StyleStructContext aContext);
   nsStyleTextReset(const nsStyleTextReset& aOther);
   ~nsStyleTextReset();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleTextReset* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleTextReset, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStyleTextReset();
@@ -2020,16 +2030,17 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsSt
   mozilla::StyleComplexColor mTextDecorationColor; // [reset]
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleText
 {
   explicit nsStyleText(StyleStructContext aContext);
   nsStyleText(const nsStyleText& aOther);
   ~nsStyleText();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleText* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleText, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStyleText();
@@ -2238,16 +2249,17 @@ protected:
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleVisibility
 {
   explicit nsStyleVisibility(StyleStructContext aContext);
   nsStyleVisibility(const nsStyleVisibility& aVisibility);
   ~nsStyleVisibility() {
     MOZ_COUNT_DTOR(nsStyleVisibility);
   }
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleVisibility* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleVisibility, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStyleVisibility();
@@ -2745,16 +2757,17 @@ using StyleShapeOutside = StyleShapeSour
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleDisplay
 {
   explicit nsStyleDisplay(StyleStructContext aContext);
   nsStyleDisplay(const nsStyleDisplay& aOther);
   ~nsStyleDisplay() {
     MOZ_COUNT_DTOR(nsStyleDisplay);
   }
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleDisplay* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleDisplay, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStyleDisplay();
@@ -3056,16 +3069,17 @@ public:
   inline mozilla::StyleClear PhysicalBreakType(mozilla::WritingMode aWM) const;
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleTable
 {
   explicit nsStyleTable(StyleStructContext aContext);
   nsStyleTable(const nsStyleTable& aOther);
   ~nsStyleTable();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleTable* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleTable, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStyleTable();
@@ -3087,16 +3101,17 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsSt
   int32_t       mSpan;          // [reset] the number of columns spanned by a colgroup or col
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleTableBorder
 {
   explicit nsStyleTableBorder(StyleStructContext aContext);
   nsStyleTableBorder(const nsStyleTableBorder& aOther);
   ~nsStyleTableBorder();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleTableBorder* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleTableBorder, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStyleTableBorder();
@@ -3195,16 +3210,17 @@ struct nsStyleCounterData
   }
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleContent
 {
   explicit nsStyleContent(StyleStructContext aContext);
   nsStyleContent(const nsStyleContent& aContent);
   ~nsStyleContent();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleContent* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleContent, sz);
   }
   void Destroy(nsPresContext* aContext);
 
@@ -3277,16 +3293,17 @@ protected:
   nsTArray<nsStyleCounterData> mResets;
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleUIReset
 {
   explicit nsStyleUIReset(StyleStructContext aContext);
   nsStyleUIReset(const nsStyleUIReset& aOther);
   ~nsStyleUIReset();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleUIReset* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleUIReset, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStyleUIReset();
@@ -3349,16 +3366,17 @@ private:
   nsCOMPtr<imgIRequest> mImage;
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleUserInterface
 {
   explicit nsStyleUserInterface(StyleStructContext aContext);
   nsStyleUserInterface(const nsStyleUserInterface& aOther);
   ~nsStyleUserInterface();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleUserInterface* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleUserInterface, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStyleUserInterface();
@@ -3392,16 +3410,17 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsSt
   inline uint8_t GetEffectivePointerEvents(nsIFrame* aFrame) const;
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleXUL
 {
   explicit nsStyleXUL(StyleStructContext aContext);
   nsStyleXUL(const nsStyleXUL& aSource);
   ~nsStyleXUL();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleXUL* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleXUL, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStyleXUL();
@@ -3431,16 +3450,17 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsSt
   bool          mStretchStack;          // [reset] see nsStyleConsts.h
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleColumn
 {
   explicit nsStyleColumn(StyleStructContext aContext);
   nsStyleColumn(const nsStyleColumn& aSource);
   ~nsStyleColumn();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleColumn* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleColumn, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStyleColumn();
@@ -3555,16 +3575,17 @@ private:
   nscolor mFallbackColor;
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleSVG
 {
   explicit nsStyleSVG(StyleStructContext aContext);
   nsStyleSVG(const nsStyleSVG& aSource);
   ~nsStyleSVG();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleSVG* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleSVG, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStyleSVG();
@@ -3688,16 +3709,17 @@ private:
   uint8_t          mContextFlags;     // [inherited]
 };
 
 struct nsStyleFilter
 {
   nsStyleFilter();
   nsStyleFilter(const nsStyleFilter& aSource);
   ~nsStyleFilter();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   nsStyleFilter& operator=(const nsStyleFilter& aOther);
 
   bool operator==(const nsStyleFilter& aOther) const;
   bool operator!=(const nsStyleFilter& aOther) const {
     return !(*this == aOther);
   }
 
@@ -3744,16 +3766,17 @@ struct nsTArray_CopyChooser<nsStyleFilte
   typedef nsTArray_CopyWithConstructors<nsStyleFilter> Type;
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleSVGReset
 {
   explicit nsStyleSVGReset(StyleStructContext aContext);
   nsStyleSVGReset(const nsStyleSVGReset& aSource);
   ~nsStyleSVGReset();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleSVGReset* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleSVGReset, sz);
   }
   void Destroy(nsPresContext* aContext);
 
@@ -3796,16 +3819,17 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsSt
   uint8_t          mMaskType;         // [reset] see nsStyleConsts.h
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleVariables
 {
   explicit nsStyleVariables(StyleStructContext aContext);
   nsStyleVariables(const nsStyleVariables& aSource);
   ~nsStyleVariables();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleVariables* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleVariables, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStyleVariables();
@@ -3826,16 +3850,17 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsSt
   mozilla::CSSVariableValues mVariables;
 };
 
 struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleEffects
 {
   explicit nsStyleEffects(StyleStructContext aContext);
   nsStyleEffects(const nsStyleEffects& aSource);
   ~nsStyleEffects();
+  void FinishStyle(nsPresContext* aPresContext) {}
 
   void* operator new(size_t sz, nsStyleEffects* aSelf) { return aSelf; }
   void* operator new(size_t sz, nsPresContext* aContext) {
     return aContext->PresShell()->
       AllocateByObjectID(mozilla::eArenaObjectID_nsStyleEffects, sz);
   }
   void Destroy(nsPresContext* aContext) {
     this->~nsStyleEffects();