diff --git a/js/public/ProtoKey.h b/js/public/ProtoKey.h
index ad133fd5c2de..da589c8c773c 100644
--- a/js/public/ProtoKey.h
+++ b/js/public/ProtoKey.h
@@ -59,20 +59,6 @@
 #  define IF_WASM_JSPI(REAL, IMAGINARY) IMAGINARY
 #endif
 
-// IF_EXPLICIT_RESOURCE_MANAGEMENT is already used elsewhere.
-#ifdef ENABLE_EXPLICIT_RESOURCE_MANAGEMENT
-#  define IF_HAVE_EXPLICIT_RESOURCE_MANAGEMENT(REAL, IMAGINARY) REAL
-#else
-#  define IF_HAVE_EXPLICIT_RESOURCE_MANAGEMENT(REAL, IMAGINARY) IMAGINARY
-#endif
-
-// IF_RECORD_TUPLE is already used elsewhere.
-#ifdef ENABLE_RECORD_TUPLE
-#  define IF_HAVE_RECORD_TUPLE(REAL, IMAGINARY) REAL
-#else
-#  define IF_HAVE_RECORD_TUPLE(REAL, IMAGINARY) IMAGINARY
-#endif
-
 #ifdef NIGHTLY_BUILD
 #  define IF_NIGHTLY(REAL, IMAGINARY) REAL
 #else
@@ -81,8 +67,7 @@
 
 #define JS_FOR_PROTOTYPES_(REAL, IMAGINARY, REAL_IF_INTL, REAL_IF_TEMPORAL, \
                            REAL_IF_WASM_TYPE, REAL_IF_WASM_JSPI,            \
-                           REAL_IF_EXPLICIT_RESOURCE_MANAGEMENT,            \
-                           REAL_IF_RECORD_TUPLE, REAL_IF_NIGHTLY)           \
+                           REAL_IF_NIGHTLY)                                 \
   IMAGINARY(Null, dummy)                                                    \
   REAL(Object, OCLASP(Plain))                                               \
   REAL(Function, &FunctionClass)                                            \
@@ -101,8 +86,8 @@
   REAL(EvalError, ERROR_CLASP(JSEXN_EVALERR))                               \
   REAL(RangeError, ERROR_CLASP(JSEXN_RANGEERR))                             \
   REAL(ReferenceError, ERROR_CLASP(JSEXN_REFERENCEERR))                     \
-  REAL_IF_EXPLICIT_RESOURCE_MANAGEMENT(SuppressedError,                     \
-                                       ERROR_CLASP(JSEXN_SUPPRESSEDERR))    \
+  IF_EXPLICIT_RESOURCE_MANAGEMENT(                                          \
+      REAL(SuppressedError, ERROR_CLASP(JSEXN_SUPPRESSEDERR)))              \
   REAL(SyntaxError, ERROR_CLASP(JSEXN_SYNTAXERR))                           \
   REAL(TypeError, ERROR_CLASP(JSEXN_TYPEERR))                               \
   REAL(URIError, ERROR_CLASP(JSEXN_URIERR))                                 \
@@ -166,10 +151,10 @@
   REAL(WeakRef, OCLASP(WeakRef))                                            \
   REAL(Iterator, OCLASP(Iterator))                                          \
   REAL(AsyncIterator, OCLASP(AsyncIterator))                                \
-  REAL_IF_EXPLICIT_RESOURCE_MANAGEMENT(DisposableStack,                     \
-                                       OCLASP(DisposableStack))             \
-  REAL_IF_EXPLICIT_RESOURCE_MANAGEMENT(AsyncDisposableStack,                \
-                                       OCLASP(AsyncDisposableStack))        \
+  IF_EXPLICIT_RESOURCE_MANAGEMENT(                                          \
+      REAL(DisposableStack, OCLASP(DisposableStack)))                       \
+  IF_EXPLICIT_RESOURCE_MANAGEMENT(                                          \
+      REAL(AsyncDisposableStack, OCLASP(AsyncDisposableStack)))             \
   REAL_IF_TEMPORAL(Temporal, OCLASP(temporal::Temporal))                    \
   REAL_IF_TEMPORAL(Duration, OCLASP(temporal::Duration))                    \
   REAL_IF_TEMPORAL(Instant, OCLASP(temporal::Instant))                      \
@@ -180,24 +165,14 @@
   REAL_IF_TEMPORAL(PlainTime, OCLASP(temporal::PlainTime))                  \
   REAL_IF_TEMPORAL(TemporalNow, OCLASP(temporal::TemporalNow))              \
   REAL_IF_TEMPORAL(ZonedDateTime, OCLASP(temporal::ZonedDateTime))          \
-  REAL_IF_RECORD_TUPLE(Record, (&RecordType::class_))                       \
-  REAL_IF_RECORD_TUPLE(Tuple, (&TupleType::class_))
-// DO NOT ADD CONDITIONAL ENTRIES TO THIS LIST! (As in, do not add entries that
-// are only present in some configurations.) It will break binary compatibility.
-// Instead, create an IF_<feature> macro and add it to the parameter list below
-// and add a corresponding parameter to JS_FOR_PROTOTYPES_ above.
-//
-// Note that entries may be freely added to or removed from this list, even in
-// the middle. The only invariant that must be upheld is that the offsets in the
-// list do not change depending on configuration settings of the same version of
-// the source.
+  IF_RECORD_TUPLE(REAL(Record, (&RecordType::class_)))                      \
+  IF_RECORD_TUPLE(REAL(Tuple, (&TupleType::class_)))
 
 #define JS_FOR_PROTOTYPES(REAL, IMAGINARY)                                     \
   JS_FOR_PROTOTYPES_(                                                          \
       REAL, IMAGINARY, IF_INTL(REAL, IMAGINARY), IF_TEMPORAL(REAL, IMAGINARY), \
       IF_WASM_TYPE(REAL, IMAGINARY), IF_WASM_JSPI(REAL, IMAGINARY),            \
-      IF_HAVE_EXPLICIT_RESOURCE_MANAGEMENT(REAL, IMAGINARY),                   \
-      IF_HAVE_RECORD_TUPLE(REAL, IMAGINARY), IF_NIGHTLY(REAL, IMAGINARY))
+      IF_NIGHTLY(REAL, IMAGINARY))
 
 #define JS_FOR_EACH_PROTOTYPE(MACRO) JS_FOR_PROTOTYPES(MACRO, MACRO)
 
diff --git a/mfbt/MaybeStorageBase.h b/mfbt/MaybeStorageBase.h
index 90ca2230d2d9..9469d427eb33 100644
--- a/mfbt/MaybeStorageBase.h
+++ b/mfbt/MaybeStorageBase.h
@@ -63,7 +63,7 @@ struct MaybeStorageBase<T, true> {
   using NonConstT = std::remove_const_t<T>;
 
   union Union {
-    constexpr Union() : empty{} {}
+    constexpr Union() : empty() {}
     constexpr explicit Union(const T& aVal) : val{aVal} {}
     constexpr explicit Union(T&& aVal) : val{std::move(aVal)} {}
     template <typename... Args>
@@ -71,8 +71,7 @@ struct MaybeStorageBase<T, true> {
         : val{std::forward<Args>(aArgs)...} {}
 
     NonConstT val;
-    struct {
-    } empty;
+    char empty;
   } mStorage;
 
  public: