--- a/dom/html/HTMLFontElement.cpp
+++ b/dom/html/HTMLFontElement.cpp
@@ -50,71 +50,58 @@ HTMLFontElement::ParseAttribute(int32_t 
   }
 
   return nsGenericHTMLElement::ParseAttribute(aNamespaceID, aAttribute, aValue,
                                               aResult);
 }
 
 void
 HTMLFontElement::MapAttributesIntoRule(const nsMappedAttributes* aAttributes,
-                                       GenericSpecifiedValues* aGenericData)
+                                       GenericSpecifiedValues* aData)
 {
-  nsRuleData* aData = aGenericData->AsRuleData();
-  if (aData->mSIDs & NS_STYLE_INHERIT_BIT(Font)) {
+  if (aData->ShouldComputeStyleStruct(NS_STYLE_INHERIT_BIT(Font))) {
     // face: string list
-    nsCSSValue* family = aData->ValueForFontFamily();
-    if (family->GetUnit() == eCSSUnit_Null) {
+    if (!aData->PropertyIsSet(eCSSProperty_font_family)) {
       const nsAttrValue* value = aAttributes->GetAttr(nsGkAtoms::face);
       if (value && value->Type() == nsAttrValue::eString &&
           !value->IsEmptyString()) {
-        nsCSSParser parser;
-        parser.ParseFontFamilyListString(value->GetStringValue(),
-                                         nullptr, 0, *family);
+        aData->SetFontFamily(value->GetStringValue());
       }
     }
-
     // size: int
-    nsCSSValue* fontSize = aData->ValueForFontSize();
-    if (fontSize->GetUnit() == eCSSUnit_Null) {
+    if (!aData->PropertyIsSet(eCSSProperty_font_size)) {
       const nsAttrValue* value = aAttributes->GetAttr(nsGkAtoms::size);
-      if (value && value->Type() == nsAttrValue::eInteger) {
-        fontSize->SetIntValue(value->GetIntegerValue(), eCSSUnit_Enumerated);
-      }
+      if (value && value->Type() == nsAttrValue::eInteger)
+        aData->SetKeywordValue(eCSSProperty_font_size, value->GetIntegerValue());
     }
   }
-  if (aData->mSIDs & NS_STYLE_INHERIT_BIT(Color)) {
-    nsCSSValue* colorValue = aData->ValueForColor();
-    if (colorValue->GetUnit() == eCSSUnit_Null &&
-        aData->mPresContext->UseDocumentColors()) {
+  if (aData->ShouldComputeStyleStruct(NS_STYLE_INHERIT_BIT(Color))) {
+    if (!aData->PropertyIsSet(eCSSProperty_color) &&
+        aData->PresContext()->UseDocumentColors()) {
       // color: color
       const nsAttrValue* value = aAttributes->GetAttr(nsGkAtoms::color);
       nscolor color;
       if (value && value->GetColorValue(color)) {
-        colorValue->SetColorValue(color);
+        aData->SetColorValue(eCSSProperty_color, color);
       }
     }
   }
-  if (aData->mSIDs & NS_STYLE_INHERIT_BIT(TextReset) &&
-      aData->mPresContext->CompatibilityMode() == eCompatibility_NavQuirks) {
+  if (aData->ShouldComputeStyleStruct(NS_STYLE_INHERIT_BIT(TextReset)) &&
+      aData->PresContext()->CompatibilityMode() == eCompatibility_NavQuirks) {
     // Make <a><font color="red">text</font></a> give the text a red underline
     // in quirks mode.  The NS_STYLE_TEXT_DECORATION_LINE_OVERRIDE_ALL flag only
     // affects quirks mode rendering.
     const nsAttrValue* value = aAttributes->GetAttr(nsGkAtoms::color);
     nscolor color;
     if (value && value->GetColorValue(color)) {
-      nsCSSValue* decoration = aData->ValueForTextDecorationLine();
-      int32_t newValue = NS_STYLE_TEXT_DECORATION_LINE_OVERRIDE_ALL;
-      if (decoration->GetUnit() == eCSSUnit_Enumerated) {
-        newValue |= decoration->GetIntValue();
-      }
-      decoration->SetIntValue(newValue, eCSSUnit_Enumerated);
+      aData->SetTextDecorationColorOverride();
     }
   }
 
-  nsGenericHTMLElement::MapCommonAttributesInto(aAttributes, aGenericData);
+  nsGenericHTMLElement::MapCommonAttributesInto(aAttributes, aData);
 }
 
 NS_IMETHODIMP_(bool)
 HTMLFontElement::IsAttributeMapped(const nsIAtom* aAttribute) const
 {
   static const MappedAttributeEntry attributes[] = {
     { &nsGkAtoms::face },
     { &nsGkAtoms::size },

--- a/layout/style/GenericSpecifiedValues.h
+++ b/layout/style/GenericSpecifiedValues.h
@@ -73,12 +73,17 @@ public:
     // Set a property to `currentcolor`
     virtual void SetCurrentColor(nsCSSPropertyID aId) = 0;
     virtual void SetCurrentColorIfUnset(nsCSSPropertyID aId) = 0;
 
     // Set a property to an RGBA nscolor value
     virtual void SetColorValue(nsCSSPropertyID aId, nscolor aValue) = 0;
     virtual void SetColorValueIfUnset(nsCSSPropertyID aId, nscolor aValue) = 0;
 
+    // Set font-family to a string
+    virtual void SetFontFamily(const nsString& aValue) = 0;
+    // Add a quirks-mode override to the decoration color of elements nested in <a>
+    virtual void SetTextDecorationColorOverride() = 0;
+
     virtual nsRuleData* AsRuleData() = 0;
 };
 
 #endif // mozilla_GenericSpecifiedValues_h

--- a/layout/style/nsRuleData.cpp
+++ b/layout/style/nsRuleData.cpp
@@ -1,15 +1,16 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nsRuleData.h"
 
+#include "nsCSSParser.h"
 #include "mozilla/Poison.h"
 #include <stdint.h>
 
 inline size_t
 nsRuleData::GetPoisonOffset()
 {
   // Fill in mValueOffsets such that mValueStorage + mValueOffsets[i]
   // will yield the frame poison value for all uninitialized value
@@ -35,16 +36,35 @@ nsRuleData::nsRuleData(uint32_t aSIDs, n
 #ifndef MOZ_VALGRIND
   size_t framePoisonOffset = GetPoisonOffset();
   for (size_t i = 0; i < nsStyleStructID_Length; ++i) {
     mValueOffsets[i] = framePoisonOffset;
   }
 #endif
 }
 
+void
+nsRuleData::SetFontFamily(const nsString& aValue)
+{
+  nsCSSValue* family = ValueForFontFamily();
+  nsCSSParser parser;
+  parser.ParseFontFamilyListString(aValue, nullptr, 0, *family);
+}
+
+void
+nsRuleData::SetTextDecorationColorOverride()
+{
+  nsCSSValue* decoration = ValueForTextDecorationLine();
+  int32_t newValue = NS_STYLE_TEXT_DECORATION_LINE_OVERRIDE_ALL;
+  if (decoration->GetUnit() == eCSSUnit_Enumerated) {
+    newValue |= decoration->GetIntValue();
+  }
+  decoration->SetIntValue(newValue, eCSSUnit_Enumerated);
+}
+
 #ifdef DEBUG
 nsRuleData::~nsRuleData()
 {
 #ifndef MOZ_VALGRIND
   // assert nothing in mSIDs has poison value
   size_t framePoisonOffset = GetPoisonOffset();
   for (size_t i = 0; i < nsStyleStructID_Length; ++i) {
     MOZ_ASSERT(!(mSIDs & (1 << i)) || mValueOffsets[i] != framePoisonOffset,

--- a/layout/style/nsRuleData.h
+++ b/layout/style/nsRuleData.h
@@ -215,16 +215,19 @@ struct nsRuleData final: GenericSpecifie
 
   void SetColorValueIfUnset(nsCSSPropertyID aId,
                             nscolor aValue) override {
     if (!PropertyIsSet(aId)) {
       SetColorValue(aId, aValue);
     }
   }
 
+  void SetFontFamily(const nsString& aValue) override;
+  void SetTextDecorationColorOverride() override;
+
   nsRuleData* AsRuleData() override {
     return this;
   }
 
 private:
   inline size_t GetPoisonOffset();
 
 };