--- a/layout/style/CounterStyleManager.cpp
+++ b/layout/style/CounterStyleManager.cpp
@@ -2039,32 +2039,31 @@ CounterStyle*
 CounterStyleManager::BuildCounterStyle(nsIAtom* aName)
 {
   MOZ_ASSERT(NS_IsMainThread());
   CounterStyle* data = GetCounterStyle(aName);
   if (data) {
     return data;
   }
 
-  // It is intentional that the predefined names are case-insensitive
-  // but the user-defined names case-sensitive.
+  // Names are compared case-sensitively here. Predefined names should
+  // have been lowercased by the parser.
   StyleSetHandle styleSet = mPresContext->StyleSet();
   nsCSSCounterStyleRule* rule = styleSet->CounterStyleRuleForName(aName);
   if (rule) {
     MOZ_ASSERT(rule->Name() == aName);
     data = new (mPresContext) CustomCounterStyle(aName, this, rule);
   } else {
-    int32_t type;
-    nsDependentAtomString name(aName);
-    nsCSSKeyword keyword = nsCSSKeywords::LookupKeyword(name);
-    if (nsCSSProps::FindKeyword(keyword, nsCSSProps::kListStyleKTable, type)) {
-      if (gBuiltinStyleTable[type].IsDependentStyle()) {
-        data = new (mPresContext) DependentBuiltinCounterStyle(type, this);
-      } else {
-        data = GetBuiltinStyle(type);
+    for (const BuiltinCounterStyle& item : gBuiltinStyleTable) {
+      if (item.GetStyleName() == aName) {
+        int32_t style = item.GetStyle();
+        data = item.IsDependentStyle()
+          ? new (mPresContext) DependentBuiltinCounterStyle(style, this)
+          : GetBuiltinStyle(style);
+        break;
       }
     }
   }
   if (!data) {
     data = GetDecimalStyle();
   }
   mStyles.Put(aName, data);
   return data;
@@ -2077,16 +2076,24 @@ CounterStyleManager::GetBuiltinStyle(int
              "Require a valid builtin style constant");
   MOZ_ASSERT(!gBuiltinStyleTable[aStyle].IsDependentStyle(),
              "Cannot get dependent builtin style");
   // No method of BuiltinCounterStyle mutates the struct itself, so it
   // should be fine to cast const away.
   return const_cast<BuiltinCounterStyle*>(&gBuiltinStyleTable[aStyle]);
 }
 
+/* static */ nsIAtom*
+CounterStyleManager::GetStyleNameFromType(int32_t aStyle)
+{
+  MOZ_ASSERT(0 <= aStyle && size_t(aStyle) < sizeof(gBuiltinStyleTable),
+             "Require a valid builtin style constant");
+  return gBuiltinStyleTable[aStyle].GetStyleName();
+}
+
 bool
 CounterStyleManager::NotifyRuleChanged()
 {
   bool changed = false;
   for (auto iter = mStyles.Iter(); !iter.Done(); iter.Next()) {
     CounterStyle* style = iter.Data();
     bool toBeUpdated = false;
     bool toBeRemoved = false;

--- a/layout/style/CounterStyleManager.h
+++ b/layout/style/CounterStyleManager.h
@@ -340,16 +340,18 @@ public:
   {
     return GetBuiltinStyle(NS_STYLE_LIST_STYLE_DECIMAL);
   }
   static CounterStyle* GetDiscStyle()
   {
     return GetBuiltinStyle(NS_STYLE_LIST_STYLE_DISC);
   }
 
+  static nsIAtom* GetStyleNameFromType(int32_t aStyle);
+
   // This method will scan all existing counter styles generated by this
   // manager, and remove or mark data dirty accordingly. It returns true
   // if any counter style is changed, false elsewise. This method should
   // be called when any counter style may be affected.
   bool NotifyRuleChanged();
   // NotifyRuleChanged will evict no longer needed counter styles into
   // mRetiredStyles, and this function destroys all objects listed there.
   // It should be called only after no one may ever use those objects.

--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -8088,36 +8088,37 @@ nsRuleNode::ComputeListData(void* aStart
     }
     case eCSSUnit_String: {
       nsString str;
       typeValue->GetStringValue(str);
       list->mCounterStyle = new AnonymousCounterStyle(str);
       break;
     }
     case eCSSUnit_Enumerated: {
-      // For compatibility with html attribute map.
-      // This branch should never be called for value from CSS.
+      // For compatibility with html attribute map. This branch should
+      // never be called for value from CSS. The values can only come
+      // from the items in EnumTable listed in HTMLLIElement.cpp and
+      // HTMLSharedListElement.cpp.
       int32_t intValue = typeValue->GetIntValue();
       nsCOMPtr<nsIAtom> name;
       switch (intValue) {
         case NS_STYLE_LIST_STYLE_LOWER_ROMAN:
           name = nsGkAtoms::lowerRoman;
           break;
         case NS_STYLE_LIST_STYLE_UPPER_ROMAN:
           name = nsGkAtoms::upperRoman;
           break;
         case NS_STYLE_LIST_STYLE_LOWER_ALPHA:
           name = nsGkAtoms::lowerAlpha;
           break;
         case NS_STYLE_LIST_STYLE_UPPER_ALPHA:
           name = nsGkAtoms::upperAlpha;
           break;
         default:
-          name = NS_Atomize(nsCSSProps::ValueToKeyword(
-                  intValue, nsCSSProps::kListStyleKTable));
+          name = CounterStyleManager::GetStyleNameFromType(intValue);
           break;
       }
       setListStyleType(name);
       break;
     }
     case eCSSUnit_Symbols:
       list->mCounterStyle =
         new AnonymousCounterStyle(typeValue->GetArrayValue());