--- a/layout/style/nsCSSValue.cpp
+++ b/layout/style/nsCSSValue.cpp
@@ -150,20 +150,16 @@ nsCSSValue::nsCSSValue(const nsCSSValue&
   else if (eCSSUnit_Image == mUnit) {
     mValue.mImage = aCopy.mValue.mImage;
     mValue.mImage->AddRef();
   }
   else if (eCSSUnit_Pair == mUnit) {
     mValue.mPair = aCopy.mValue.mPair;
     mValue.mPair->AddRef();
   }
-  else if (eCSSUnit_Triplet == mUnit) {
-    mValue.mTriplet = aCopy.mValue.mTriplet;
-    mValue.mTriplet->AddRef();
-  }
   else if (eCSSUnit_Rect == mUnit) {
     mValue.mRect = aCopy.mValue.mRect;
     mValue.mRect->AddRef();
   }
   else if (eCSSUnit_List == mUnit) {
     mValue.mList = aCopy.mValue.mList;
     mValue.mList->AddRef();
   }
@@ -246,19 +242,16 @@ bool nsCSSValue::operator==(const nsCSSV
       return mValue.mURL->Equals(*aOther.mValue.mURL);
     }
     else if (eCSSUnit_Image == mUnit) {
       return mValue.mImage->Equals(*aOther.mValue.mImage);
     }
     else if (eCSSUnit_Pair == mUnit) {
       return *mValue.mPair == *aOther.mValue.mPair;
     }
-    else if (eCSSUnit_Triplet == mUnit) {
-      return *mValue.mTriplet == *aOther.mValue.mTriplet;
-    }
     else if (eCSSUnit_Rect == mUnit) {
       return *mValue.mRect == *aOther.mValue.mRect;
     }
     else if (eCSSUnit_List == mUnit) {
       return nsCSSValueList::Equal(mValue.mList, aOther.mValue.mList);
     }
     else if (eCSSUnit_SharedList == mUnit) {
       return *mValue.mSharedList == *aOther.mValue.mSharedList;
@@ -373,18 +366,16 @@ void nsCSSValue::DoReset()
   } else if (UnitHasArrayValue()) {
     DO_RELEASE(mArray);
   } else if (eCSSUnit_URL == mUnit) {
     DO_RELEASE(mURL);
   } else if (eCSSUnit_Image == mUnit) {
     DO_RELEASE(mImage);
   } else if (eCSSUnit_Pair == mUnit) {
     DO_RELEASE(mPair);
-  } else if (eCSSUnit_Triplet == mUnit) {
-    DO_RELEASE(mTriplet);
   } else if (eCSSUnit_Rect == mUnit) {
     DO_RELEASE(mRect);
   } else if (eCSSUnit_List == mUnit) {
     DO_RELEASE(mList);
   } else if (eCSSUnit_SharedList == mUnit) {
     DO_RELEASE(mSharedList);
   } else if (eCSSUnit_PairList == mUnit) {
     DO_RELEASE(mPairList);
@@ -528,62 +519,16 @@ void nsCSSValue::SetPairValue(const nsCS
              yValue.GetUnit() != eCSSUnit_Unset,
              "inappropriate pair value");
   Reset();
   mUnit = eCSSUnit_Pair;
   mValue.mPair = new nsCSSValuePair_heap(xValue, yValue);
   mValue.mPair->AddRef();
 }
 
-void nsCSSValue::SetTripletValue(const nsCSSValueTriplet* aValue)
-{
-  // triplet should not be used for null/inherit/initial values
-  MOZ_ASSERT(aValue &&
-             aValue->mXValue.GetUnit() != eCSSUnit_Null &&
-             aValue->mYValue.GetUnit() != eCSSUnit_Null &&
-             aValue->mZValue.GetUnit() != eCSSUnit_Null &&
-             aValue->mXValue.GetUnit() != eCSSUnit_Inherit &&
-             aValue->mYValue.GetUnit() != eCSSUnit_Inherit &&
-             aValue->mZValue.GetUnit() != eCSSUnit_Inherit &&
-             aValue->mXValue.GetUnit() != eCSSUnit_Initial &&
-             aValue->mYValue.GetUnit() != eCSSUnit_Initial &&
-             aValue->mZValue.GetUnit() != eCSSUnit_Initial &&
-             aValue->mXValue.GetUnit() != eCSSUnit_Unset &&
-             aValue->mYValue.GetUnit() != eCSSUnit_Unset &&
-             aValue->mZValue.GetUnit() != eCSSUnit_Unset,
-             "missing or inappropriate triplet value");
-  Reset();
-  mUnit = eCSSUnit_Triplet;
-  mValue.mTriplet = new nsCSSValueTriplet_heap(aValue->mXValue, aValue->mYValue, aValue->mZValue);
-  mValue.mTriplet->AddRef();
-}
-
-void nsCSSValue::SetTripletValue(const nsCSSValue& xValue,
-                                 const nsCSSValue& yValue,
-                                 const nsCSSValue& zValue)
-{
-  // Only allow Null for the z component
-  MOZ_ASSERT(xValue.GetUnit() != eCSSUnit_Null &&
-             yValue.GetUnit() != eCSSUnit_Null &&
-             xValue.GetUnit() != eCSSUnit_Inherit &&
-             yValue.GetUnit() != eCSSUnit_Inherit &&
-             zValue.GetUnit() != eCSSUnit_Inherit &&
-             xValue.GetUnit() != eCSSUnit_Initial &&
-             yValue.GetUnit() != eCSSUnit_Initial &&
-             zValue.GetUnit() != eCSSUnit_Initial &&
-             xValue.GetUnit() != eCSSUnit_Unset &&
-             yValue.GetUnit() != eCSSUnit_Unset &&
-             zValue.GetUnit() != eCSSUnit_Unset,
-             "inappropriate triplet value");
-  Reset();
-  mUnit = eCSSUnit_Triplet;
-  mValue.mTriplet = new nsCSSValueTriplet_heap(xValue, yValue, zValue);
-  mValue.mTriplet->AddRef();
-}
-
 nsCSSRect& nsCSSValue::SetRectValue()
 {
   Reset();
   mUnit = eCSSUnit_Rect;
   mValue.mRect = new nsCSSRect_heap;
   mValue.mRect->AddRef();
   return *mValue.mRect;
 }
@@ -934,21 +879,16 @@ nsCSSValue::SizeOfExcludingThis(mozilla:
       n += mValue.mImage->SizeOfIncludingThis(aMallocSizeOf);
       break;
 
     // Pair
     case eCSSUnit_Pair:
       n += mValue.mPair->SizeOfIncludingThis(aMallocSizeOf);
       break;
 
-    // Triplet
-    case eCSSUnit_Triplet:
-      n += mValue.mTriplet->SizeOfIncludingThis(aMallocSizeOf);
-      break;
-
     // Rect
     case eCSSUnit_Rect:
       n += mValue.mRect->SizeOfIncludingThis(aMallocSizeOf);
       break;
 
     // List
     case eCSSUnit_List:
       n += mValue.mList->SizeOfIncludingThis(aMallocSizeOf);
@@ -1207,32 +1147,16 @@ nsCSSValuePair_heap::SizeOfIncludingThis
   if (mRefCnt <= 1) {
     n += aMallocSizeOf(this);
     n += mXValue.SizeOfExcludingThis(aMallocSizeOf);
     n += mYValue.SizeOfExcludingThis(aMallocSizeOf);
   }
   return n;
 }
 
-// --- nsCSSValueTriplet -----------------
-
-size_t
-nsCSSValueTriplet_heap::SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
-{
-  // Only measure it if it's unshared, to avoid double-counting.
-  size_t n = 0;
-  if (mRefCnt <= 1) {
-    n += aMallocSizeOf(this);
-    n += mXValue.SizeOfExcludingThis(aMallocSizeOf);
-    n += mYValue.SizeOfExcludingThis(aMallocSizeOf);
-    n += mZValue.SizeOfExcludingThis(aMallocSizeOf);
-  }
-  return n;
-}
-
 // --- nsCSSValuePairList -----------------
 
 nsCSSValuePairList::~nsCSSValuePairList()
 {
   MOZ_COUNT_DTOR(nsCSSValuePairList);
   NS_CSS_DELETE_LIST_MEMBER(nsCSSValuePairList, this, mNext);
 }
 

--- a/layout/style/nsCSSValue.h
+++ b/layout/style/nsCSSValue.h
@@ -402,17 +402,16 @@ enum nsCSSUnit {
   eCSSUnit_Calc_Divided = 35,     // (nsCSSValue::Array*) / within calc
 
   eCSSUnit_URL          = 40,     // (nsCSSValue::URL*) value
   eCSSUnit_Image        = 41,     // (nsCSSValue::Image*) value
   eCSSUnit_GridTemplateAreas   = 44,   // (GridTemplateAreasValue*)
                                        // for grid-template-areas
 
   eCSSUnit_Pair         = 50,     // (nsCSSValuePair*) pair of values
-  eCSSUnit_Triplet      = 51,     // (nsCSSValueTriplet*) triplet of values
   eCSSUnit_Rect         = 52,     // (nsCSSRect*) rectangle (four values)
   eCSSUnit_List         = 53,     // (nsCSSValueList*) list of values
   eCSSUnit_ListDep      = 54,     // (nsCSSValueList*) same as List
                                   //   but does not own the list
   eCSSUnit_SharedList   = 55,     // (nsCSSValueSharedList*) same as list
                                   //   but reference counted and shared
   eCSSUnit_PairList     = 56,     // (nsCSSValuePairList*) list of value pairs
   eCSSUnit_PairListDep  = 57,     // (nsCSSValuePairList*) same as PairList
@@ -473,18 +472,16 @@ struct nsCSSValuePair;
 struct nsCSSValuePair_heap;
 struct nsCSSRect;
 struct nsCSSRect_heap;
 struct nsCSSValueList;
 struct nsCSSValueList_heap;
 struct nsCSSValueSharedList;
 struct nsCSSValuePairList;
 struct nsCSSValuePairList_heap;
-struct nsCSSValueTriplet;
-struct nsCSSValueTriplet_heap;
 
 class nsCSSValue {
 public:
   struct Array;
   friend struct Array;
 
   friend struct mozilla::css::URLValueData;
 
@@ -668,20 +665,16 @@ public:
   inline const nsCSSRect& GetRectValue() const;
 
   inline nsCSSValueList* GetListValue();
   inline const nsCSSValueList* GetListValue() const;
 
   inline nsCSSValuePairList* GetPairListValue();
   inline const nsCSSValuePairList* GetPairListValue() const;
 
-  inline nsCSSValueTriplet& GetTripletValue();
-  inline const nsCSSValueTriplet& GetTripletValue() const;
-
-
   mozilla::css::URLValue* GetURLStructValue() const
   {
     // Not allowing this for Image values, because if the caller takes
     // a ref to them they won't be able to delete them properly.
     MOZ_ASSERT(mUnit == eCSSUnit_URL, "not a URL value");
     return mValue.mURL;
   }
 
@@ -753,18 +746,16 @@ public:
   void SetImageValue(mozilla::css::ImageValue* aImage);
   void SetGridTemplateAreas(mozilla::css::GridTemplateAreasValue* aValue);
   void SetFontFamilyListValue(already_AddRefed<mozilla::SharedFontList> aFontListValue);
   void SetPairValue(const nsCSSValuePair* aPair);
   void SetPairValue(const nsCSSValue& xValue, const nsCSSValue& yValue);
   void SetSharedListValue(nsCSSValueSharedList* aList);
   void SetDependentListValue(nsCSSValueList* aList);
   void SetDependentPairListValue(nsCSSValuePairList* aList);
-  void SetTripletValue(const nsCSSValueTriplet* aTriplet);
-  void SetTripletValue(const nsCSSValue& xValue, const nsCSSValue& yValue, const nsCSSValue& zValue);
   void SetAutoValue();
   void SetInheritValue();
   void SetInitialValue();
   void SetUnsetValue();
   void SetNoneValue();
   void SetAllValue();
   void SetNormalValue();
   void SetSystemFontValue();
@@ -822,17 +813,16 @@ protected:
     nsStringBuffer* MOZ_OWNING_REF mString;
     nsAtom* MOZ_OWNING_REF mAtom;
     Array* MOZ_OWNING_REF mArray;
     mozilla::css::URLValue* MOZ_OWNING_REF mURL;
     mozilla::css::ImageValue* MOZ_OWNING_REF mImage;
     mozilla::css::GridTemplateAreasValue* MOZ_OWNING_REF mGridTemplateAreas;
     nsCSSValuePair_heap* MOZ_OWNING_REF mPair;
     nsCSSRect_heap* MOZ_OWNING_REF mRect;
-    nsCSSValueTriplet_heap* MOZ_OWNING_REF mTriplet;
     nsCSSValueList_heap* MOZ_OWNING_REF mList;
     nsCSSValueList* mListDependent;
     nsCSSValueSharedList* MOZ_OWNING_REF mSharedList;
     nsCSSValuePairList_heap* MOZ_OWNING_REF mPairList;
     nsCSSValuePairList* mPairListDependent;
     mozilla::SharedFontList* MOZ_OWNING_REF mFontFamilyList;
   } mValue;
 };
@@ -1189,134 +1179,32 @@ struct nsCSSValuePair_heap final : publi
 
 private:
   // Private destructor, to discourage deletion outside of Release():
   ~nsCSSValuePair_heap()
   {
   }
 };
 
-struct nsCSSValueTriplet {
-    nsCSSValueTriplet()
-    {
-        MOZ_COUNT_CTOR(nsCSSValueTriplet);
-    }
-    explicit nsCSSValueTriplet(nsCSSUnit aUnit)
-        : mXValue(aUnit), mYValue(aUnit), mZValue(aUnit)
-    {
-        MOZ_COUNT_CTOR(nsCSSValueTriplet);
-    }
-    nsCSSValueTriplet(const nsCSSValue& aXValue,
-                      const nsCSSValue& aYValue,
-                      const nsCSSValue& aZValue)
-        : mXValue(aXValue), mYValue(aYValue), mZValue(aZValue)
-    {
-        MOZ_COUNT_CTOR(nsCSSValueTriplet);
-    }
-    nsCSSValueTriplet(const nsCSSValueTriplet& aCopy)
-        : mXValue(aCopy.mXValue), mYValue(aCopy.mYValue), mZValue(aCopy.mZValue)
-    {
-        MOZ_COUNT_CTOR(nsCSSValueTriplet);
-    }
-    ~nsCSSValueTriplet()
-    {
-        MOZ_COUNT_DTOR(nsCSSValueTriplet);
-    }
-
-    bool operator==(const nsCSSValueTriplet& aOther) const {
-        return mXValue == aOther.mXValue &&
-               mYValue == aOther.mYValue &&
-               mZValue == aOther.mZValue;
-    }
-
-    bool operator!=(const nsCSSValueTriplet& aOther) const {
-        return mXValue != aOther.mXValue ||
-               mYValue != aOther.mYValue ||
-               mZValue != aOther.mZValue;
-    }
-
-    bool AllValuesEqualTo(const nsCSSValue& aValue) const {
-        return mXValue == aValue &&
-               mYValue == aValue &&
-               mZValue == aValue;
-    }
-
-    void SetAllValuesTo(const nsCSSValue& aValue) {
-        mXValue = aValue;
-        mYValue = aValue;
-        mZValue = aValue;
-    }
-
-    void Reset() {
-        mXValue.Reset();
-        mYValue.Reset();
-        mZValue.Reset();
-    }
-
-    bool HasValue() const {
-        return mXValue.GetUnit() != eCSSUnit_Null ||
-               mYValue.GetUnit() != eCSSUnit_Null ||
-               mZValue.GetUnit() != eCSSUnit_Null;
-    }
-
-    nsCSSValue mXValue;
-    nsCSSValue mYValue;
-    nsCSSValue mZValue;
-};
-
-// nsCSSValueTriplet_heap differs from nsCSSValueTriplet only in being
-// refcounted.  It should not be necessary to use this class directly;
-// it's an implementation detail of nsCSSValue.
-struct nsCSSValueTriplet_heap final : public nsCSSValueTriplet {
-  // forward constructor
-  nsCSSValueTriplet_heap(const nsCSSValue& aXValue, const nsCSSValue& aYValue, const nsCSSValue& aZValue)
-    : nsCSSValueTriplet(aXValue, aYValue, aZValue)
-  {}
-
-  NS_INLINE_DECL_REFCOUNTING(nsCSSValueTriplet_heap)
-
-  size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
-
-private:
-  // Private destructor, to discourage deletion outside of Release():
-  ~nsCSSValueTriplet_heap()
-  {
-  }
-};
-
 // This has to be here so that the relationship between nsCSSValuePair
 // and nsCSSValuePair_heap is visible.
 inline nsCSSValuePair&
 nsCSSValue::GetPairValue()
 {
   MOZ_ASSERT(mUnit == eCSSUnit_Pair, "not a pair value");
   return *mValue.mPair;
 }
 
 inline const nsCSSValuePair&
 nsCSSValue::GetPairValue() const
 {
   MOZ_ASSERT(mUnit == eCSSUnit_Pair, "not a pair value");
   return *mValue.mPair;
 }
 
-inline nsCSSValueTriplet&
-nsCSSValue::GetTripletValue()
-{
-    MOZ_ASSERT(mUnit == eCSSUnit_Triplet, "not a triplet value");
-    return *mValue.mTriplet;
-}
-
-inline const nsCSSValueTriplet&
-nsCSSValue::GetTripletValue() const
-{
-    MOZ_ASSERT(mUnit == eCSSUnit_Triplet, "not a triplet value");
-    return *mValue.mTriplet;
-}
-
 // Maybe should be replaced with nsCSSValueList and nsCSSValue::Array?
 struct nsCSSValuePairList {
   nsCSSValuePairList() : mNext(nullptr) { MOZ_COUNT_CTOR(nsCSSValuePairList); }
   ~nsCSSValuePairList();
 
   nsCSSValuePairList* Clone() const; // makes a deep copy. Infallible.
 
   static bool Equal(const nsCSSValuePairList* aList1,