diff --git a/layout/style/Declaration.cpp b/layout/style/Declaration.cpp
index c6f679a8cb43..53b920782b44 100644
--- a/layout/style/Declaration.cpp
+++ b/layout/style/Declaration.cpp
@@ -1022,7 +1022,7 @@ Declaration::GetValue(nsCSSProperty aProperty, nsAString& aValue,
         // which isn't a value that the shorthand can express. Bail.
         return;
       }
-      const GridTemplateAreasValue& areas = areasValue.GetGridTemplateAreas();
+      const GridTemplateAreasValue* areas = areasValue.GetGridTemplateAreas();
       const nsCSSValueList* rowsItem = rowsValue.GetListValue();
       uint32_t nRowItems = 0;
       while (rowsItem) {
@@ -1030,7 +1030,7 @@ Declaration::GetValue(nsCSSProperty aProperty, nsAString& aValue,
         rowsItem = rowsItem->mNext;
       }
       MOZ_ASSERT(nRowItems % 2 == 1, "expected an odd number of items");
-      if ((nRowItems - 1) / 2 != areas.NRows()) {
+      if ((nRowItems - 1) / 2 != areas->NRows()) {
         // Not serializable, bail.
         return;
       }
@@ -1057,7 +1057,7 @@ Declaration::GetValue(nsCSSProperty aProperty, nsAString& aValue,
           aValue.AppendLiteral(")");
 
         } else {
-          nsStyleUtil::AppendEscapedCSSString(areas.mTemplates[row++], aValue);
+          nsStyleUtil::AppendEscapedCSSString(areas->mTemplates[row++], aValue);
           aValue.Append(char16_t(' '));
 
           // <track-size>
diff --git a/layout/style/nsCSSParser.cpp b/layout/style/nsCSSParser.cpp
index e6cd085742b6..8d94aa940848 100644
--- a/layout/style/nsCSSParser.cpp
+++ b/layout/style/nsCSSParser.cpp
@@ -673,7 +673,7 @@ protected:
   // |aAreaIndices| is a lookup table to help us parse faster,
   // mapping area names to indices in |aResult.mNamedAreas|.
   bool ParseGridTemplateAreasLine(const nsAutoString& aInput,
-                                  css::GridTemplateAreasValue& aResult,
+                                  css::GridTemplateAreasValue* aResult,
                                   nsDataHashtable<nsStringHashKey, uint32_t>& aAreaIndices);
   bool ParseGridTemplateAreas();
   bool ParseGridTemplate();
@@ -7156,15 +7156,15 @@ CSSParserImpl::ParseGridTemplateColumnsRows(nsCSSProperty aPropID)
 
 bool
 CSSParserImpl::ParseGridTemplateAreasLine(const nsAutoString& aInput,
-                                          css::GridTemplateAreasValue& aAreas,
+                                          css::GridTemplateAreasValue* aAreas,
                                           nsDataHashtable<nsStringHashKey, uint32_t>& aAreaIndices)
 {
-  aAreas.mTemplates.AppendElement(mToken.mIdent);
+  aAreas->mTemplates.AppendElement(mToken.mIdent);
 
   nsCSSGridTemplateAreaScanner scanner(aInput);
   nsCSSGridTemplateAreaToken token;
   css::GridNamedArea* currentArea = nullptr;
-  uint32_t row = aAreas.NRows();
+  uint32_t row = aAreas->NRows();
   uint32_t column;
   for (column = 1; scanner.Next(token); column++) {
     if (token.isTrash) {
@@ -7194,9 +7194,9 @@ CSSParserImpl::ParseGridTemplateAreasLine(const nsAutoString& aInput,
       // Check if this is the continuation of an existing named area:
       uint32_t index;
       if (aAreaIndices.Get(token.mName, &index)) {
-        MOZ_ASSERT(index < aAreas.mNamedAreas.Length(),
+        MOZ_ASSERT(index < aAreas->mNamedAreas.Length(),
                    "Invalid aAreaIndices hash table");
-        currentArea = &aAreas.mNamedAreas[index];
+        currentArea = &aAreas->mNamedAreas[index];
         if (currentArea->mColumnStart != column ||
             currentArea->mRowEnd != row) {
           // Existing named area, but not forming a rectangle
@@ -7206,8 +7206,8 @@ CSSParserImpl::ParseGridTemplateAreasLine(const nsAutoString& aInput,
         currentArea->mRowEnd++;
       } else {
         // New named area
-        aAreaIndices.Put(token.mName, aAreas.mNamedAreas.Length());
-        currentArea = aAreas.mNamedAreas.AppendElement();
+        aAreaIndices.Put(token.mName, aAreas->mNamedAreas.Length());
+        currentArea = aAreas->mNamedAreas.AppendElement();
         currentArea->mName = token.mName;
         // For column or row N (starting at 1),
         // the start line is N, the end line is N + 1
@@ -7230,8 +7230,8 @@ CSSParserImpl::ParseGridTemplateAreasLine(const nsAutoString& aInput,
   // On other rows, check that the number of columns is consistent
   // between rows.
   if (row == 1) {
-    aAreas.mNColumns = column;
-  } else if (aAreas.mNColumns != column) {
+    aAreas->mNColumns = column;
+  } else if (aAreas->mNColumns != column) {
     return false;
   }
   return true;
@@ -7246,7 +7246,8 @@ CSSParserImpl::ParseGridTemplateAreas()
     return true;
   }
 
-  css::GridTemplateAreasValue& areas = value.SetGridTemplateAreas();
+  nsRefPtr<css::GridTemplateAreasValue> areas =
+    new css::GridTemplateAreasValue();
   nsDataHashtable<nsStringHashKey, uint32_t> areaIndices;
   for (;;) {
     if (!GetToken(true)) {
@@ -7261,11 +7262,11 @@ CSSParserImpl::ParseGridTemplateAreas()
     }
   }
 
-  if (areas.NRows() == 0) {
+  if (areas->NRows() == 0) {
     return false;
   }
 
-  AppendValue(eCSSProperty_grid_template_areas, value);
+  AppendValue(eCSSProperty_grid_template_areas, nsCSSValue(areas));
   return true;
 }
 
@@ -7366,9 +7367,9 @@ CSSParserImpl::ParseGridTemplateAfterString(const nsCSSValue& aFirstLineNames)
   MOZ_ASSERT(mToken.mType == eCSSToken_String,
              "ParseGridTemplateAfterString called with a non-string token");
 
-  nsCSSValue areasValue;
   nsCSSValue rowsValue;
-  css::GridTemplateAreasValue& areas = areasValue.SetGridTemplateAreas();
+  nsRefPtr<css::GridTemplateAreasValue> areas =
+    new css::GridTemplateAreasValue();
   nsDataHashtable<nsStringHashKey, uint32_t> areaIndices;
   nsCSSValueList* rowsItem = rowsValue.SetListValue();
   rowsItem->mValue = aFirstLineNames;
@@ -7410,7 +7411,7 @@ CSSParserImpl::ParseGridTemplateAfterString(const nsCSSValue& aFirstLineNames)
     }
   }
 
-  AppendValue(eCSSProperty_grid_template_areas, areasValue);
+  AppendValue(eCSSProperty_grid_template_areas, nsCSSValue(areas));
   AppendValue(eCSSProperty_grid_template_rows, rowsValue);
   return true;
 }
diff --git a/layout/style/nsCSSValue.cpp b/layout/style/nsCSSValue.cpp
index fa25349bd768..712ec1c958e7 100644
--- a/layout/style/nsCSSValue.cpp
+++ b/layout/style/nsCSSValue.cpp
@@ -104,6 +104,13 @@ nsCSSValue::nsCSSValue(nsCSSValueTokenStream* aValue)
   mValue.mTokenStream->AddRef();
 }
 
+nsCSSValue::nsCSSValue(mozilla::css::GridTemplateAreasValue* aValue)
+  : mUnit(eCSSUnit_GridTemplateAreas)
+{
+  mValue.mGridTemplateAreas = aValue;
+  mValue.mGridTemplateAreas->AddRef();
+}
+
 nsCSSValue::nsCSSValue(const nsCSSValue& aCopy)
   : mUnit(aCopy.mUnit)
 {
@@ -460,6 +467,14 @@ void nsCSSValue::SetTokenStreamValue(nsCSSValueTokenStream* aValue)
   mValue.mTokenStream->AddRef();
 }
 
+void nsCSSValue::SetGridTemplateAreas(mozilla::css::GridTemplateAreasValue* aValue)
+{
+  Reset();
+  mUnit = eCSSUnit_GridTemplateAreas;
+  mValue.mGridTemplateAreas = aValue;
+  mValue.mGridTemplateAreas->AddRef();
+}
+
 void nsCSSValue::SetPairValue(const nsCSSValuePair* aValue)
 {
   // pairs should not be used for null/inherit/initial values
@@ -596,15 +611,6 @@ void nsCSSValue::SetDependentPairListValue(nsCSSValuePairList* aList)
   }
 }
 
-mozilla::css::GridTemplateAreasValue& nsCSSValue::SetGridTemplateAreas()
-{
-  Reset();
-  mUnit = eCSSUnit_GridTemplateAreas;
-  mValue.mGridTemplateAreas = new mozilla::css::GridTemplateAreasValue;
-  mValue.mGridTemplateAreas->AddRef();
-  return *mValue.mGridTemplateAreas;
-}
-
 void nsCSSValue::SetAutoValue()
 {
   Reset();
@@ -1345,13 +1351,13 @@ nsCSSValue::AppendToString(nsCSSProperty aProperty, nsAString& aResult,
         break;
     }
   } else if (eCSSUnit_GridTemplateAreas == unit) {
-    const mozilla::css::GridTemplateAreasValue& areas = GetGridTemplateAreas();
-    MOZ_ASSERT(!areas.mTemplates.IsEmpty(),
+    const mozilla::css::GridTemplateAreasValue* areas = GetGridTemplateAreas();
+    MOZ_ASSERT(!areas->mTemplates.IsEmpty(),
                "Unexpected empty array in GridTemplateAreasValue");
-    nsStyleUtil::AppendEscapedCSSString(areas.mTemplates[0], aResult);
-    for (uint32_t i = 1; i < areas.mTemplates.Length(); i++) {
+    nsStyleUtil::AppendEscapedCSSString(areas->mTemplates[0], aResult);
+    for (uint32_t i = 1; i < areas->mTemplates.Length(); i++) {
       aResult.Append(char16_t(' '));
-      nsStyleUtil::AppendEscapedCSSString(areas.mTemplates[i], aResult);
+      nsStyleUtil::AppendEscapedCSSString(areas->mTemplates[i], aResult);
     }
   }
 
diff --git a/layout/style/nsCSSValue.h b/layout/style/nsCSSValue.h
index 01fa40073cd0..753938ce9d9d 100644
--- a/layout/style/nsCSSValue.h
+++ b/layout/style/nsCSSValue.h
@@ -144,7 +144,7 @@ struct GridNamedArea {
   uint32_t mRowEnd;
 };
 
-struct GridTemplateAreasValue {
+struct GridTemplateAreasValue MOZ_FINAL {
   // Parsed value
   nsTArray<GridNamedArea> mNamedAreas;
 
@@ -168,13 +168,6 @@ struct GridTemplateAreasValue {
   {
   }
 
-  void Reset()
-  {
-    mNamedAreas.Clear();
-    mTemplates.Clear();
-    mNColumns = 0;
-  }
-
   bool operator==(const GridTemplateAreasValue& aOther) const
   {
     return mTemplates == aOther.mTemplates;
@@ -188,6 +181,17 @@ struct GridTemplateAreasValue {
   NS_INLINE_DECL_REFCOUNTING(GridTemplateAreasValue)
 
   size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
+
+private:
+  // Private destructor to make sure this isn't used as a stack variable
+  // or member variable.
+  ~GridTemplateAreasValue()
+  {
+  }
+
+  GridTemplateAreasValue(const GridTemplateAreasValue& aOther) MOZ_DELETE;
+  GridTemplateAreasValue&
+  operator=(const GridTemplateAreasValue& aOther) MOZ_DELETE;
 };
 
 }
@@ -247,6 +251,8 @@ enum nsCSSUnit {
   eCSSUnit_Image        = 41,     // (nsCSSValue::Image*) value
   eCSSUnit_Gradient     = 42,     // (nsCSSValueGradient*) value
   eCSSUnit_TokenStream  = 43,     // (nsCSSValueTokenStream*) value
+  eCSSUnit_GridTemplateAreas   = 44,   // (GridTemplateAreasValue*)
+                                       // for grid-template-areas
 
   eCSSUnit_Pair         = 50,     // (nsCSSValuePair*) pair of values
   eCSSUnit_Triplet      = 51,     // (nsCSSValueTriplet*) triplet of values
@@ -260,8 +266,6 @@ enum nsCSSUnit {
   eCSSUnit_PairListDep  = 57,     // (nsCSSValuePairList*) same as PairList
                                   //   but does not own the list
 
-  eCSSUnit_GridTemplateAreas   = 60,   // (GridTemplateAreasValue*) for grid-template-areas
-
   eCSSUnit_Integer      = 70,     // (int) simple value
   eCSSUnit_Enumerated   = 71,     // (int) value has enumerated meaning
 
@@ -359,6 +363,7 @@ public:
   explicit nsCSSValue(mozilla::css::ImageValue* aValue);
   explicit nsCSSValue(nsCSSValueGradient* aValue);
   explicit nsCSSValue(nsCSSValueTokenStream* aValue);
+  explicit nsCSSValue(mozilla::css::GridTemplateAreasValue* aValue);
   nsCSSValue(const nsCSSValue& aCopy);
   ~nsCSSValue() { Reset(); }
 
@@ -553,8 +558,6 @@ public:
   inline nsCSSValueTriplet& GetTripletValue();
   inline const nsCSSValueTriplet& GetTripletValue() const;
 
-  inline mozilla::css::GridTemplateAreasValue& GetGridTemplateAreas();
-  inline const mozilla::css::GridTemplateAreasValue& GetGridTemplateAreas() const;
 
   mozilla::css::URLValue* GetURLStructValue() const
   {
@@ -570,6 +573,13 @@ public:
     return mValue.mImage;
   }
 
+  mozilla::css::GridTemplateAreasValue* GetGridTemplateAreas() const
+  {
+    NS_ABORT_IF_FALSE(mUnit == eCSSUnit_GridTemplateAreas,
+                      "not a grid-template-areas value");
+    return mValue.mGridTemplateAreas;
+  }
+
   const char16_t* GetOriginalURLValue() const
   {
     NS_ABORT_IF_FALSE(mUnit == eCSSUnit_URL || mUnit == eCSSUnit_Image,
@@ -611,6 +621,7 @@ public:
   void SetImageValue(mozilla::css::ImageValue* aImage);
   void SetGradientValue(nsCSSValueGradient* aGradient);
   void SetTokenStreamValue(nsCSSValueTokenStream* aTokenStream);
+  void SetGridTemplateAreas(mozilla::css::GridTemplateAreasValue* aValue);
   void SetPairValue(const nsCSSValuePair* aPair);
   void SetPairValue(const nsCSSValue& xValue, const nsCSSValue& yValue);
   void SetSharedListValue(nsCSSValueSharedList* aList);
@@ -634,7 +645,6 @@ public:
   nsCSSRect& SetRectValue();
   nsCSSValueList* SetListValue();
   nsCSSValuePairList* SetPairListValue();
-  mozilla::css::GridTemplateAreasValue& SetGridTemplateAreas();
 
   void StartImageLoad(nsIDocument* aDocument) const;  // Only pretend const
 
@@ -1246,22 +1256,6 @@ nsCSSValue::GetPairListValue() const
   }
 }
 
-inline mozilla::css::GridTemplateAreasValue&
-nsCSSValue::GetGridTemplateAreas()
-{
-  NS_ABORT_IF_FALSE (mUnit == eCSSUnit_GridTemplateAreas,
-                     "not a grid-template-areas value");
-  return *mValue.mGridTemplateAreas;
-}
-
-inline const mozilla::css::GridTemplateAreasValue&
-nsCSSValue::GetGridTemplateAreas() const
-{
-  NS_ABORT_IF_FALSE (mUnit == eCSSUnit_GridTemplateAreas,
-                     "not a grid-template-areas value");
-  return *mValue.mGridTemplateAreas;
-}
-
 struct nsCSSValueGradientStop {
 public:
   nsCSSValueGradientStop();
diff --git a/layout/style/nsComputedDOMStyle.cpp b/layout/style/nsComputedDOMStyle.cpp
index ef2d5c681019..2aca0edf1420 100644
--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -2274,18 +2274,20 @@ nsComputedDOMStyle::DoGetBackgroundSize()
 CSSValue*
 nsComputedDOMStyle::DoGetGridTemplateAreas()
 {
-  const nsTArray<nsString>& templates =
-    StylePosition()->mGridTemplateAreas.mTemplates;
-  if (templates.IsEmpty()) {
+  const css::GridTemplateAreasValue* areas =
+    StylePosition()->mGridTemplateAreas;
+  if (!areas) {
     nsROCSSPrimitiveValue *val = new nsROCSSPrimitiveValue;
     val->SetIdent(eCSSKeyword_none);
     return val;
   }
 
+  MOZ_ASSERT(!areas->mTemplates.IsEmpty(),
+             "Unexpected empty array in GridTemplateAreasValue");
   nsDOMCSSValueList *valueList = GetROCSSValueList(false);
-  for (uint32_t i = 0; i < templates.Length(); i++) {
+  for (uint32_t i = 0; i < areas->mTemplates.Length(); i++) {
     nsAutoString str;
-    nsStyleUtil::AppendEscapedCSSString(templates[i], str);
+    nsStyleUtil::AppendEscapedCSSString(areas->mTemplates[i], str);
     nsROCSSPrimitiveValue *val = new nsROCSSPrimitiveValue;
     val->SetString(str);
     valueList->AppendCSSValue(val);
diff --git a/layout/style/nsRuleNode.cpp b/layout/style/nsRuleNode.cpp
index d3ec80d084af..81081c122c24 100644
--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -7234,8 +7234,8 @@ SetGridTrackList(const nsCSSValue& aValue,
 
 static void
 SetGridTemplateAreas(const nsCSSValue& aValue,
-                     css::GridTemplateAreasValue& aResult,
-                     const css::GridTemplateAreasValue& aParentValue,
+                     nsRefPtr<css::GridTemplateAreasValue>* aResult,
+                     css::GridTemplateAreasValue* aParentValue,
                      bool& aCanStoreInRuleTree)
 {
   switch (aValue.GetUnit()) {
@@ -7244,17 +7244,17 @@ SetGridTemplateAreas(const nsCSSValue& aValue,
 
   case eCSSUnit_Inherit:
     aCanStoreInRuleTree = false;
-    aResult = aParentValue;
+    *aResult = aParentValue;
     break;
 
   case eCSSUnit_Initial:
   case eCSSUnit_Unset:
   case eCSSUnit_None:
-    aResult.Reset();
+    *aResult = nullptr;
     break;
 
   default:
-    aResult = aValue.GetGridTemplateAreas();
+    *aResult = aValue.GetGridTemplateAreas();
   }
 }
 
@@ -7521,7 +7521,8 @@ nsRuleNode::ComputePositionData(void* aStartStruct,
 
   // grid-tempate-areas
   SetGridTemplateAreas(*aRuleData->ValueForGridTemplateAreas(),
-                       pos->mGridTemplateAreas, parentPos->mGridTemplateAreas,
+                       &pos->mGridTemplateAreas,
+                       parentPos->mGridTemplateAreas,
                        canStoreInRuleTree);
 
   // grid-auto-position
diff --git a/layout/style/nsStyleStruct.cpp b/layout/style/nsStyleStruct.cpp
index e8ac7646338a..8bb041faa631 100644
--- a/layout/style/nsStyleStruct.cpp
+++ b/layout/style/nsStyleStruct.cpp
@@ -1254,12 +1254,11 @@ nsStylePosition::nsStylePosition(void)
   mZIndex.SetAutoValue();
   mGridAutoPositionColumn.SetToInteger(1);
   mGridAutoPositionRow.SetToInteger(1);
-  // mGridTemplateRows, mGridTemplateColumns, and mGridTemplateAreas
-  // get their default constructors
-  // which initialize them to empty arrays,
-  // which represent the properties' initial value 'none'.
-
-  // mGrid{Column,Row}{Start,End} get their default constructor, 'auto'
+  // Other members get their default constructors
+  // which initialize them to representations of their respective initial value.
+  // mGridTemplateAreas: nullptr for 'none'
+  // mGridTemplate{Rows,Columns}: empty arrays for 'none'
+  // mGrid{Column,Row}{Start,End}: false/0/empty values for 'auto'
 }
 
 nsStylePosition::~nsStylePosition(void)
diff --git a/layout/style/nsStyleStruct.h b/layout/style/nsStyleStruct.h
index 14c914258e0b..e388e0f3bd06 100644
--- a/layout/style/nsStyleStruct.h
+++ b/layout/style/nsStyleStruct.h
@@ -1300,7 +1300,9 @@ struct nsStylePosition {
   // in nsStyleStruct.cpp
   nsStyleGridTrackList mGridTemplateColumns;
   nsStyleGridTrackList mGridTemplateRows;
-  mozilla::css::GridTemplateAreasValue mGridTemplateAreas;
+
+  // nullptr for 'none'
+  nsRefPtr<mozilla::css::GridTemplateAreasValue> mGridTemplateAreas;
 
   // We represent the "grid-auto-position" property in two parts:
   nsStyleGridLine mGridAutoPositionColumn;