diff --git a/layout/inspector/inDOMUtils.cpp b/layout/inspector/inDOMUtils.cpp
index 03ca9c400327..ed4da113cf73 100644
--- a/layout/inspector/inDOMUtils.cpp
+++ b/layout/inspector/inDOMUtils.cpp
@@ -459,8 +459,8 @@ inDOMUtils::SelectorMatchesElement(nsIDOMElement* aElement,
     // We need to make sure that the requested pseudo element type
     // matches the selector pseudo element type before proceeding.
     nsCOMPtr<nsIAtom> pseudoElt = NS_Atomize(aPseudo);
-    if (sel->mSelectors->PseudoType() != nsCSSPseudoElements::
-          GetPseudoType(pseudoElt, CSSEnabledState::eIgnoreEnabledState)) {
+    if (sel->mSelectors->PseudoType() !=
+        nsCSSPseudoElements::GetPseudoType(pseudoElt)) {
       *aMatches = false;
       return NS_OK;
     }
@@ -1233,7 +1233,7 @@ inDOMUtils::GetCSSPseudoElementNames(uint32_t* aLength, char16_t*** aNames)
     static_cast<CSSPseudoElementTypeBase>(CSSPseudoElementType::Count);
   for (CSSPseudoElementTypeBase i = 0; i < pseudoCount; ++i) {
     CSSPseudoElementType type = static_cast<CSSPseudoElementType>(i);
-    if (nsCSSPseudoElements::IsEnabled(type, CSSEnabledState::eForAllContent)) {
+    if (!nsCSSPseudoElements::PseudoElementIsUASheetOnly(type)) {
       nsIAtom* atom = nsCSSPseudoElements::GetPseudoAtom(type);
       array.AppendElement(atom);
     }
diff --git a/layout/style/nsCSSParser.cpp b/layout/style/nsCSSParser.cpp
index 1ec301595c1e..f4f6e4f2ab50 100644
--- a/layout/style/nsCSSParser.cpp
+++ b/layout/style/nsCSSParser.cpp
@@ -5916,12 +5916,20 @@ CSSParserImpl::ParsePseudoSelector(int32_t&       aDataMask,
   bool isTreePseudo = false;
   CSSEnabledState enabledState = EnabledState();
   CSSPseudoElementType pseudoElementType =
-    nsCSSPseudoElements::GetPseudoType(pseudo, enabledState);
+    nsCSSPseudoElements::GetPseudoType(pseudo);
   CSSPseudoClassType pseudoClassType =
     nsCSSPseudoClasses::GetPseudoType(pseudo, enabledState);
   bool pseudoClassIsUserAction =
     nsCSSPseudoClasses::IsUserActionPseudoClass(pseudoClassType);
 
+  if (pseudoElementType < CSSPseudoElementType::Count && !AgentRulesEnabled() &&
+      nsCSSPseudoElements::PseudoElementIsUASheetOnly(pseudoElementType)) {
+    // This pseudo-element is not exposed to content.
+    REPORT_UNEXPECTED_TOKEN(PEPseudoSelUnknown);
+    UngetToken();
+    return eSelectorParsingStatus_Error;
+  }
+
   if (nsCSSAnonBoxes::IsNonElement(pseudo)) {
     // Non-element anonymous boxes should not match any rule.
     REPORT_UNEXPECTED_TOKEN(PEPseudoSelUnknown);
diff --git a/layout/style/nsCSSPseudoElements.cpp b/layout/style/nsCSSPseudoElements.cpp
index 237b6310c838..3323c5412ce7 100644
--- a/layout/style/nsCSSPseudoElements.cpp
+++ b/layout/style/nsCSSPseudoElements.cpp
@@ -36,8 +36,7 @@ static const nsStaticAtom CSSPseudoElements_info[] = {
 // Flags data for each of the pseudo-elements, which must be separate
 // from the previous array since there's no place for it in
 // nsStaticAtom.
-/* static */ const uint32_t
-nsCSSPseudoElements::kPseudoElementFlags[Type::Count] = {
+static const uint32_t CSSPseudoElements_flags[] = {
 #define CSS_PSEUDO_ELEMENT(name_, value_, flags_) \
   flags_,
 #include "nsCSSPseudoElementList.h"
@@ -68,22 +67,20 @@ nsCSSPseudoElements::IsCSS2PseudoElement(nsIAtom *aAtom)
                   aAtom == nsCSSPseudoElements::firstLetter ||
                   aAtom == nsCSSPseudoElements::firstLine;
   NS_ASSERTION(nsCSSAnonBoxes::IsAnonBox(aAtom) ||
-               result == PseudoElementHasFlags(
-                   GetPseudoType(aAtom, EnabledState::eIgnoreEnabledState),
-                   CSS_PSEUDO_ELEMENT_IS_CSS2),
+               result == PseudoElementHasFlags(GetPseudoType(aAtom),
+                                               CSS_PSEUDO_ELEMENT_IS_CSS2),
                "result doesn't match flags");
   return result;
 }
 
 /* static */ CSSPseudoElementType
-nsCSSPseudoElements::GetPseudoType(nsIAtom *aAtom, EnabledState aEnabledState)
+nsCSSPseudoElements::GetPseudoType(nsIAtom *aAtom)
 {
   for (CSSPseudoElementTypeBase i = 0;
        i < ArrayLength(CSSPseudoElements_info);
        ++i) {
     if (*CSSPseudoElements_info[i].mAtom == aAtom) {
-      auto type = static_cast<Type>(i);
-      return IsEnabled(type, aEnabledState) ? type : Type::NotPseudo;
+      return static_cast<Type>(i);
     }
   }
 
@@ -108,6 +105,15 @@ nsCSSPseudoElements::GetPseudoAtom(Type aType)
     static_cast<CSSPseudoElementTypeBase>(aType)].mAtom;
 }
 
+/* static */ uint32_t
+nsCSSPseudoElements::FlagsForPseudoElement(const Type aType)
+{
+  CSSPseudoElementTypeBase index = static_cast<CSSPseudoElementTypeBase>(aType);
+  NS_ASSERTION(index < ArrayLength(CSSPseudoElements_flags),
+               "argument must be a pseudo-element");
+  return CSSPseudoElements_flags[index];
+}
+
 /* static */ bool
 nsCSSPseudoElements::PseudoElementSupportsUserActionState(const Type aType)
 {
diff --git a/layout/style/nsCSSPseudoElements.h b/layout/style/nsCSSPseudoElements.h
index 157b206747cd..a3f7c16aa766 100644
--- a/layout/style/nsCSSPseudoElements.h
+++ b/layout/style/nsCSSPseudoElements.h
@@ -9,7 +9,6 @@
 #define nsCSSPseudoElements_h___
 
 #include "nsIAtom.h"
-#include "mozilla/CSSEnabledState.h"
 
 // Is this pseudo-element a CSS2 pseudo-element that can be specified
 // with the single colon syntax (in addition to the double-colon syntax,
@@ -66,7 +65,6 @@ class nsICSSPseudoElement : public nsIAtom {};
 class nsCSSPseudoElements
 {
   typedef mozilla::CSSPseudoElementType Type;
-  typedef mozilla::CSSEnabledState EnabledState;
 
 public:
   static void AddRefAtoms();
@@ -80,7 +78,7 @@ public:
 #include "nsCSSPseudoElementList.h"
 #undef CSS_PSEUDO_ELEMENT
 
-  static Type GetPseudoType(nsIAtom* aAtom, EnabledState aEnabledState);
+  static Type GetPseudoType(nsIAtom* aAtom);
 
   // Get the atom for a given Type.  aType must be < CSSPseudoElementType::Count
   static nsIAtom* GetPseudoAtom(Type aType);
@@ -97,21 +95,19 @@ public:
 
   static bool PseudoElementSupportsUserActionState(const Type aType);
 
-  static bool IsEnabled(Type aType, EnabledState aEnabledState)
-  {
-    return !PseudoElementHasFlags(aType, CSS_PSEUDO_ELEMENT_UA_SHEET_ONLY) ||
-           (aEnabledState & EnabledState::eInUASheets);
+  static bool PseudoElementIsUASheetOnly(const Type aType) {
+    MOZ_ASSERT(aType < Type::Count);
+    return PseudoElementHasFlags(aType, CSS_PSEUDO_ELEMENT_UA_SHEET_ONLY);
   }
 
 private:
+  static uint32_t FlagsForPseudoElement(const Type aType);
+
   // Does the given pseudo-element have all of the flags given?
   static bool PseudoElementHasFlags(const Type aType, uint32_t aFlags)
   {
-    MOZ_ASSERT(aType < Type::Count);
-    return (kPseudoElementFlags[size_t(aType)] & aFlags) == aFlags;
+    return (FlagsForPseudoElement(aType) & aFlags) == aFlags;
   }
-
-  static const uint32_t kPseudoElementFlags[Type::Count];
 };
 
 #endif /* nsCSSPseudoElements_h___ */
diff --git a/layout/style/nsComputedDOMStyle.cpp b/layout/style/nsComputedDOMStyle.cpp
index beb641ddd5db..fab63d4c4a9f 100644
--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -488,8 +488,7 @@ nsComputedDOMStyle::GetStyleContextForElementNoFlush(Element* aElement,
 
   RefPtr<nsStyleContext> sc;
   if (aPseudo) {
-    CSSPseudoElementType type = nsCSSPseudoElements::
-      GetPseudoType(aPseudo, CSSEnabledState::eIgnoreEnabledState);
+    CSSPseudoElementType type = nsCSSPseudoElements::GetPseudoType(aPseudo);
     if (type >= CSSPseudoElementType::Count) {
       return nullptr;
     }
diff --git a/layout/style/nsStyleSet.cpp b/layout/style/nsStyleSet.cpp
index 0352f2d217af..8cf6b21e2c59 100644
--- a/layout/style/nsStyleSet.cpp
+++ b/layout/style/nsStyleSet.cpp
@@ -865,9 +865,8 @@ nsStyleSet::GetContext(nsStyleContext* aParentContext,
                    aPseudoType ==
                      CSSPseudoElementType::NotPseudo) ||
                   (aPseudoTag &&
-                   nsCSSPseudoElements::GetPseudoType(
-                     aPseudoTag, CSSEnabledState::eIgnoreEnabledState) ==
-                   aPseudoType),
+                   nsCSSPseudoElements::GetPseudoType(aPseudoTag) ==
+                     aPseudoType),
                   "Pseudo mismatch");
 
   if (aVisitedRuleNode == aRuleNode) {