--- a/layout/style/StyleAnimationValue.cpp
+++ b/layout/style/StyleAnimationValue.cpp
@@ -4320,16 +4320,17 @@ StyleAnimationValue::operator=(const Sty
 {
   if (this == &aOther) {
     return *this;
   }
 
   FreeValue();
 
   mUnit = aOther.mUnit;
+  mExtra = aOther.mExtra;
   switch (mUnit) {
     case eUnit_Null:
     case eUnit_Normal:
     case eUnit_Auto:
     case eUnit_None:
     case eUnit_CurrentColor:
       break;
     case eUnit_Enumerated:

--- a/layout/style/StyleAnimationValue.h
+++ b/layout/style/StyleAnimationValue.h
@@ -278,17 +278,17 @@ public:
 
   static already_AddRefed<nsCSSValue::Array>
     AppendTransformFunction(nsCSSKeyword aTransformFunction,
                             nsCSSValueList**& aListTail);
 
   /**
    * The types and values for the values that we extract and animate.
    */
-  enum Unit {
+  enum Unit : uint16_t {
     eUnit_Null, // not initialized
     eUnit_Normal,
     eUnit_Auto,
     eUnit_None,
     eUnit_Enumerated,
     eUnit_Visibility, // special case for transitions (which converts
                       // Enumerated to Visibility as needed)
     eUnit_Integer,
@@ -313,16 +313,17 @@ public:
     eUnit_Transform, // nsCSSValueList* (never null)
     eUnit_BackgroundPositionCoord, // nsCSSValueList* (never null)
     eUnit_CSSValuePairList, // nsCSSValuePairList* (never null)
     eUnit_UnparsedString // nsStringBuffer* (never null)
   };
 
 private:
   Unit mUnit;
+  uint16_t mExtra;
   union {
     int32_t mInt;
     nscoord mCoord;
     float mFloat;
     nscolor mColor;
     nsCSSValue* mCSSValue;
     nsCSSValuePair* mCSSValuePair;
     nsCSSValueTriplet* mCSSValueTriplet;
@@ -430,16 +431,17 @@ public:
     NS_ASSERTION(aUnit == eUnit_Null || aUnit == eUnit_Normal ||
                  aUnit == eUnit_Auto || aUnit == eUnit_None,
                  "must be valueless unit");
   }
   StyleAnimationValue(const StyleAnimationValue& aOther)
     : mUnit(eUnit_Null) { *this = aOther; }
   StyleAnimationValue(StyleAnimationValue&& aOther)
     : mUnit(aOther.mUnit)
+    , mExtra(aOther.mExtra)
     , mValue(aOther.mValue)
   {
     aOther.mUnit = eUnit_Null;
   }
   enum IntegerConstructorType { IntegerConstructor };
   StyleAnimationValue(int32_t aInt, Unit aUnit, IntegerConstructorType);
   enum CoordConstructorType { CoordConstructor };
   StyleAnimationValue(nscoord aLength, CoordConstructorType);

--- a/layout/style/nsCSSValue.cpp
+++ b/layout/style/nsCSSValue.cpp
@@ -134,16 +134,17 @@ nsCSSValue::nsCSSValue(css::FontFamilyLi
   : mUnit(eCSSUnit_FontFamilyList)
 {
   mValue.mFontFamilyList = aValue;
   mValue.mFontFamilyList->AddRef();
 }
 
 nsCSSValue::nsCSSValue(const nsCSSValue& aCopy)
   : mUnit(aCopy.mUnit)
+  , mExtra(aCopy.mExtra)
 {
   if (mUnit <= eCSSUnit_DummyInherit) {
     // nothing to do, but put this important case first
   }
   else if (eCSSUnit_Percent <= mUnit) {
     mValue.mFloat = aCopy.mValue.mFloat;
     MOZ_ASSERT(!mozilla::IsNaN(mValue.mFloat));
   }
@@ -235,16 +236,17 @@ nsCSSValue& nsCSSValue::operator=(const 
 
 nsCSSValue&
 nsCSSValue::operator=(nsCSSValue&& aOther)
 {
   MOZ_ASSERT(this != &aOther, "Self assigment with rvalue reference");
 
   Reset();
   mUnit = aOther.mUnit;
+  mExtra = aOther.mExtra;
   mValue = aOther.mValue;
   aOther.mUnit = eCSSUnit_Null;
 
   return *this;
 }
 
 bool nsCSSValue::operator==(const nsCSSValue& aOther) const
 {

--- a/layout/style/nsCSSValue.h
+++ b/layout/style/nsCSSValue.h
@@ -292,17 +292,17 @@ private:
     ~FontFamilyListRefCnt() {
         MOZ_COUNT_DTOR(FontFamilyListRefCnt);
     }
 };
 
 } // namespace css
 } // namespace mozilla
 
-enum nsCSSUnit {
+enum nsCSSUnit : uint16_t {
   eCSSUnit_Null         = 0,      // (n/a) null unit, value is not specified
   eCSSUnit_Auto         = 1,      // (n/a) value is algorithmic
   eCSSUnit_Inherit      = 2,      // (n/a) value is inherited
   eCSSUnit_Initial      = 3,      // (n/a) value is default UA value
   eCSSUnit_Unset        = 4,      // (n/a) value equivalent to 'initial' if on a reset property, 'inherit' otherwise
   eCSSUnit_None         = 5,      // (n/a) value is none
   eCSSUnit_Normal       = 6,      // (n/a) value is normal (algorithmic, different than auto)
   eCSSUnit_System_Font  = 7,      // (n/a) value is -moz-use-system-font
@@ -474,16 +474,17 @@ public:
   explicit nsCSSValue(mozilla::css::ImageValue* aValue);
   explicit nsCSSValue(nsCSSValueGradient* aValue);
   explicit nsCSSValue(nsCSSValueTokenStream* aValue);
   explicit nsCSSValue(mozilla::css::GridTemplateAreasValue* aValue);
   explicit nsCSSValue(mozilla::css::FontFamilyListRefCnt* aValue);
   nsCSSValue(const nsCSSValue& aCopy);
   nsCSSValue(nsCSSValue&& aOther)
     : mUnit(aOther.mUnit)
+    , mExtra(aOther.mExtra)
     , mValue(aOther.mValue)
   {
     aOther.mUnit = eCSSUnit_Null;
   }
   ~nsCSSValue() { Reset(); }
 
   nsCSSValue&  operator=(const nsCSSValue& aCopy);
   nsCSSValue&  operator=(nsCSSValue&& aCopy);
@@ -845,16 +846,17 @@ private:
            Serialization aValueSerialization) const;
   void AppendBasicShapePositionToString(
            nsAString& aResult,
            Serialization aValueSerialization) const;
   void AppendInsetToString(nsCSSPropertyID aProperty, nsAString& aResult,
                            Serialization aValueSerialization) const;
 protected:
   nsCSSUnit mUnit;
+  uint16_t mExtra;
   union {
     int32_t    mInt;
     float      mFloat;
     // Note: the capacity of the buffer may exceed the length of the string.
     // If we're of a string type, mString is not null.
     nsStringBuffer* MOZ_OWNING_REF mString;
     nscolor    mColor;
     Array* MOZ_OWNING_REF mArray;