diff --git a/js/src/frontend/BinASTTokenReaderContext.cpp b/js/src/frontend/BinASTTokenReaderContext.cpp
index 6bca93a63391..e2a9dfc8309c 100644
--- a/js/src/frontend/BinASTTokenReaderContext.cpp
+++ b/js/src/frontend/BinASTTokenReaderContext.cpp
@@ -2186,18 +2186,10 @@ HuffmanPreludeReader::readSingleValueTable<UnsignedLong>(
 }
 
 HuffmanDictionary::HuffmanDictionary(JSContext* cx)
-    : fields(cx), listLengths(cx) {
-  // Initialize `fields`. We have reserved space statically, this cannot fail.
-  for (size_t i = 0; i < BINAST_INTERFACE_AND_FIELD_LIMIT; ++i) {
-    fields.infallibleEmplaceBack(HuffmanTableUnreachable{});
-  }
-
-  // Initialize `listLengths`. We have reserved space statically, this cannot
-  // fail.
-  for (size_t i = 0; i < BINAST_NUMBER_OF_LIST_TYPES; ++i) {
-    listLengths.infallibleEmplaceBack(HuffmanTableUnreachable{});
-  }
-}
+    : fields(BINAST_PARAM_NUMBER_OF_INTERFACE_AND_FIELD(
+          mozilla::AsVariant(HuffmanTableUnreachable()))),
+      listLengths(BINAST_PARAM_NUMBER_OF_LIST_TYPES(
+          mozilla::AsVariant(HuffmanTableUnreachable()))) {}
 
 HuffmanTable& HuffmanDictionary::tableForField(
     NormalizedInterfaceAndField index) {
diff --git a/js/src/frontend/BinASTTokenReaderContext.h b/js/src/frontend/BinASTTokenReaderContext.h
index 341d140795e3..2056432d6089 100644
--- a/js/src/frontend/BinASTTokenReaderContext.h
+++ b/js/src/frontend/BinASTTokenReaderContext.h
@@ -7,10 +7,11 @@
 #ifndef frontend_BinASTTokenReaderContext_h
 #define frontend_BinASTTokenReaderContext_h
 
+#include "mozilla/Array.h"       // mozilla::Array
 #include "mozilla/Assertions.h"  // MOZ_ASSERT
 #include "mozilla/Attributes.h"  // MOZ_MUST_USE, MOZ_STACK_CLASS
-
-#include "mozilla/Maybe.h"  // mozilla::Maybe
+#include "mozilla/Maybe.h"       // mozilla::Maybe
+#include "mozilla/Variant.h"     // mozilla::Variant
 
 #include <stddef.h>  // size_t
 #include <stdint.h>  // uint8_t, uint32_t
@@ -324,7 +325,7 @@ class HuffmanDictionary {
   //
   // The mapping from `(Interface, Field) -> index` is extracted statically from
   // the webidl specs.
-  Vector<HuffmanTable, BINAST_INTERFACE_AND_FIELD_LIMIT> fields;
+  mozilla::Array<HuffmanTable, BINAST_INTERFACE_AND_FIELD_LIMIT> fields;
 
   // Huffman tables for list lengths. Some tables may be
   // `HuffmanTableUnreacheable` if they represent lists that actually do not
@@ -332,7 +333,8 @@ class HuffmanDictionary {
   //
   // The mapping from `List -> index` is extracted statically from the webidl
   // specs.
-  Vector<HuffmanTableListLength, BINAST_NUMBER_OF_LIST_TYPES> listLengths;
+  mozilla::Array<HuffmanTableListLength, BINAST_NUMBER_OF_LIST_TYPES>
+      listLengths;
 };
 
 /**