--- a/dom/html/HTMLLIElement.cpp
+++ b/dom/html/HTMLLIElement.cpp
@@ -67,30 +67,28 @@ HTMLLIElement::ParseAttribute(int32_t aN
   }
 
   return nsGenericHTMLElement::ParseAttribute(aNamespaceID, aAttribute, aValue,
                                               aResult);
 }
 
 void
 HTMLLIElement::MapAttributesIntoRule(const nsMappedAttributes* aAttributes,
-                                     GenericSpecifiedValues* aGenericData)
+                                     GenericSpecifiedValues* aData)
 {
-  nsRuleData* aData = aGenericData->AsRuleData();
-  if (aData->mSIDs & NS_STYLE_INHERIT_BIT(List)) {
-    nsCSSValue* listStyleType = aData->ValueForListStyleType();
-    if (listStyleType->GetUnit() == eCSSUnit_Null) {
+  if (aData->ShouldComputeStyleStruct(NS_STYLE_INHERIT_BIT(List))) {
+    if (!aData->PropertyIsSet(eCSSProperty_list_style_type)) {
       // type: enum
       const nsAttrValue* value = aAttributes->GetAttr(nsGkAtoms::type);
       if (value && value->Type() == nsAttrValue::eEnum)
-        listStyleType->SetIntValue(value->GetEnumValue(), eCSSUnit_Enumerated);
+        aData->SetKeywordValue(eCSSProperty_list_style_type, value->GetEnumValue());
     }
   }
 
-  nsGenericHTMLElement::MapCommonAttributesInto(aAttributes, aGenericData);
+  nsGenericHTMLElement::MapCommonAttributesInto(aAttributes, aData);
 }
 
 NS_IMETHODIMP_(bool)
 HTMLLIElement::IsAttributeMapped(const nsIAtom* aAttribute) const
 {
   static const MappedAttributeEntry attributes[] = {
     { &nsGkAtoms::type },
     { nullptr },

--- a/dom/html/HTMLPreElement.cpp
+++ b/dom/html/HTMLPreElement.cpp
@@ -42,29 +42,27 @@ HTMLPreElement::ParseAttribute(int32_t a
   }
 
   return nsGenericHTMLElement::ParseAttribute(aNamespaceID, aAttribute, aValue,
                                               aResult);
 }
 
 void
 HTMLPreElement::MapAttributesIntoRule(const nsMappedAttributes* aAttributes,
-                                      GenericSpecifiedValues* aGenericData)
+                                      GenericSpecifiedValues* aData)
 {
-  nsRuleData* aData = aGenericData->AsRuleData();
-  if (aData->mSIDs & NS_STYLE_INHERIT_BIT(Text)) {
-    nsCSSValue* whiteSpace = aData->ValueForWhiteSpace();
-    if (whiteSpace->GetUnit() == eCSSUnit_Null) {
+  if (aData->ShouldComputeStyleStruct(NS_STYLE_INHERIT_BIT(Text))) {
+    if (!aData->PropertyIsSet(eCSSProperty_white_space)) {
       // wrap: empty
       if (aAttributes->GetAttr(nsGkAtoms::wrap))
-        whiteSpace->SetIntValue(NS_STYLE_WHITESPACE_PRE_WRAP, eCSSUnit_Enumerated);
+        aData->SetKeywordValue(eCSSProperty_white_space, NS_STYLE_WHITESPACE_PRE_WRAP);
     }
   }
 
-  nsGenericHTMLElement::MapCommonAttributesInto(aAttributes, aGenericData);
+  nsGenericHTMLElement::MapCommonAttributesInto(aAttributes, aData);
 }
 
 NS_IMETHODIMP_(bool)
 HTMLPreElement::IsAttributeMapped(const nsIAtom* aAttribute) const
 {
   if (!mNodeInfo->Equals(nsGkAtoms::pre)) {
     return nsGenericHTMLElement::IsAttributeMapped(aAttribute);
   }

--- a/dom/html/HTMLSharedElement.cpp
+++ b/dom/html/HTMLSharedElement.cpp
@@ -108,35 +108,33 @@ HTMLSharedElement::ParseAttribute(int32_
   }
 
   return nsGenericHTMLElement::ParseAttribute(aNamespaceID, aAttribute, aValue,
                                               aResult);
 }
 
 static void
 DirectoryMapAttributesIntoRule(const nsMappedAttributes* aAttributes,
-                               GenericSpecifiedValues* aGenericData)
+                               GenericSpecifiedValues* aData)
 {
-  nsRuleData* aData = aGenericData->AsRuleData();
-  if (aData->mSIDs & NS_STYLE_INHERIT_BIT(List)) {
-    nsCSSValue* listStyleType = aData->ValueForListStyleType();
-    if (listStyleType->GetUnit() == eCSSUnit_Null) {
+  if (aData->ShouldComputeStyleStruct(NS_STYLE_INHERIT_BIT(List))) {
+    if (!aData->PropertyIsSet(eCSSProperty_list_style_type)) {
       // type: enum
       const nsAttrValue* value = aAttributes->GetAttr(nsGkAtoms::type);
       if (value) {
         if (value->Type() == nsAttrValue::eEnum) {
-          listStyleType->SetIntValue(value->GetEnumValue(), eCSSUnit_Enumerated);
+          aData->SetKeywordValue(eCSSProperty_list_style_type, value->GetEnumValue());
         } else {
-          listStyleType->SetIntValue(NS_STYLE_LIST_STYLE_DISC, eCSSUnit_Enumerated);
+          aData->SetKeywordValue(eCSSProperty_list_style_type, NS_STYLE_LIST_STYLE_DISC);
         }
       }
     }
   }
 
-  nsGenericHTMLElement::MapCommonAttributesInto(aAttributes, aGenericData);
+  nsGenericHTMLElement::MapCommonAttributesInto(aAttributes, aData);
 }
 
 NS_IMETHODIMP_(bool)
 HTMLSharedElement::IsAttributeMapped(const nsIAtom* aAttribute) const
 {
   if (mNodeInfo->Equals(nsGkAtoms::dir)) {
     static const MappedAttributeEntry attributes[] = {
       { &nsGkAtoms::type },

--- a/dom/html/HTMLSharedListElement.cpp
+++ b/dom/html/HTMLSharedListElement.cpp
@@ -87,31 +87,29 @@ HTMLSharedListElement::ParseAttribute(in
   }
 
   return nsGenericHTMLElement::ParseAttribute(aNamespaceID, aAttribute, aValue,
                                               aResult);
 }
 
 void
 HTMLSharedListElement::MapAttributesIntoRule(const nsMappedAttributes* aAttributes,
-                                             GenericSpecifiedValues* aGenericData)
+                                             GenericSpecifiedValues* aData)
 {
-  nsRuleData* aData = aGenericData->AsRuleData();
-  if (aData->mSIDs & NS_STYLE_INHERIT_BIT(List)) {
-    nsCSSValue* listStyleType = aData->ValueForListStyleType();
-    if (listStyleType->GetUnit() == eCSSUnit_Null) {
+  if (aData->ShouldComputeStyleStruct(NS_STYLE_INHERIT_BIT(List))) {
+    if (!aData->PropertyIsSet(eCSSProperty_list_style_type)) {
       // type: enum
       const nsAttrValue* value = aAttributes->GetAttr(nsGkAtoms::type);
       if (value && value->Type() == nsAttrValue::eEnum) {
-        listStyleType->SetIntValue(value->GetEnumValue(), eCSSUnit_Enumerated);
+        aData->SetKeywordValue(eCSSProperty_list_style_type, value->GetEnumValue());
       }
     }
   }
 
-  nsGenericHTMLElement::MapCommonAttributesInto(aAttributes, aGenericData);
+  nsGenericHTMLElement::MapCommonAttributesInto(aAttributes, aData);
 }
 
 NS_IMETHODIMP_(bool)
 HTMLSharedListElement::IsAttributeMapped(const nsIAtom* aAttribute) const
 {
   if (mNodeInfo->Equals(nsGkAtoms::ol) ||
       mNodeInfo->Equals(nsGkAtoms::ul)) {
     static const MappedAttributeEntry attributes[] = {

--- a/dom/html/HTMLTextAreaElement.cpp
+++ b/dom/html/HTMLTextAreaElement.cpp
@@ -431,33 +431,31 @@ HTMLTextAreaElement::ParseAttribute(int3
     }
   }
   return nsGenericHTMLElement::ParseAttribute(aNamespaceID, aAttribute, aValue,
                                               aResult);
 }
 
 void
 HTMLTextAreaElement::MapAttributesIntoRule(const nsMappedAttributes* aAttributes,
-                                           GenericSpecifiedValues* aGenericData)
+                                           GenericSpecifiedValues* aData)
 {
-  nsRuleData* aData = aGenericData->AsRuleData();
-  if (aData->mSIDs & NS_STYLE_INHERIT_BIT(Text)) {
+  if (aData->ShouldComputeStyleStruct(NS_STYLE_INHERIT_BIT(Text))) {
     // wrap=off
-    nsCSSValue* whiteSpace = aData->ValueForWhiteSpace();
-    if (whiteSpace->GetUnit() == eCSSUnit_Null) {
+    if (!aData->PropertyIsSet(eCSSProperty_white_space)) {
       const nsAttrValue* value = aAttributes->GetAttr(nsGkAtoms::wrap);
       if (value && value->Type() == nsAttrValue::eString &&
           value->Equals(nsGkAtoms::OFF, eIgnoreCase)) {
-        whiteSpace->SetIntValue(NS_STYLE_WHITESPACE_PRE, eCSSUnit_Enumerated);
+        aData->SetKeywordValue(eCSSProperty_white_space, NS_STYLE_WHITESPACE_PRE);
       }
     }
   }
 
-  nsGenericHTMLFormElementWithState::MapDivAlignAttributeInto(aAttributes, aGenericData);
-  nsGenericHTMLFormElementWithState::MapCommonAttributesInto(aAttributes, aGenericData);
+  nsGenericHTMLFormElementWithState::MapDivAlignAttributeInto(aAttributes, aData);
+  nsGenericHTMLFormElementWithState::MapCommonAttributesInto(aAttributes, aData);
 }
 
 nsChangeHint
 HTMLTextAreaElement::GetAttributeChangeHint(const nsIAtom* aAttribute,
                                             int32_t aModType) const
 {
   nsChangeHint retval =
       nsGenericHTMLFormElementWithState::GetAttributeChangeHint(aAttribute, aModType);