diff --git a/js/public/Class.h b/js/public/Class.h
index a2aa8bb4d36a9..abc7260949ea6 100644
--- a/js/public/Class.h
+++ b/js/public/Class.h
@@ -700,7 +700,7 @@ static const uint32_t JSCLASS_FOREGROUND_FINALIZE =
 // application.
 static const uint32_t JSCLASS_GLOBAL_APPLICATION_SLOTS = 5;
 static const uint32_t JSCLASS_GLOBAL_SLOT_COUNT =
-    JSCLASS_GLOBAL_APPLICATION_SLOTS + JSProto_LIMIT * 2 + 26;
+    JSCLASS_GLOBAL_APPLICATION_SLOTS + JSProto_LIMIT * 2 + 25;
 
 static constexpr uint32_t JSCLASS_GLOBAL_FLAGS_WITH_SLOTS(uint32_t n) {
   return JSCLASS_IS_GLOBAL |
diff --git a/js/src/builtin/FinalizationRegistryObject.cpp b/js/src/builtin/FinalizationRegistryObject.cpp
index 04e119f7c3f5b..bc9e660c3f33e 100644
--- a/js/src/builtin/FinalizationRegistryObject.cpp
+++ b/js/src/builtin/FinalizationRegistryObject.cpp
@@ -326,7 +326,6 @@ bool FinalizationRegistryObject::construct(JSContext* cx, unsigned argc,
                    recordsToBeCleanedUp.release(),
                    MemoryUse::FinalizationRegistryRecordVector);
   registry->initReservedSlot(IsQueuedForCleanupSlot, BooleanValue(false));
-  registry->initReservedSlot(IsCleanupJobActiveSlot, BooleanValue(false));
 
   if (!cx->runtime()->gc.addFinalizationRegistry(cx, registry)) {
     return false;
@@ -439,10 +438,6 @@ bool FinalizationRegistryObject::isQueuedForCleanup() const {
   return getReservedSlot(IsQueuedForCleanupSlot).toBoolean();
 }
 
-bool FinalizationRegistryObject::isCleanupJobActive() const {
-  return getReservedSlot(IsCleanupJobActiveSlot).toBoolean();
-}
-
 void FinalizationRegistryObject::queueRecordToBeCleanedUp(
     FinalizationRecordObject* record) {
   AutoEnterOOMUnsafeRegion oomUnsafe;
@@ -456,11 +451,6 @@ void FinalizationRegistryObject::setQueuedForCleanup(bool value) {
   setReservedSlot(IsQueuedForCleanupSlot, BooleanValue(value));
 }
 
-void FinalizationRegistryObject::setCleanupJobActive(bool value) {
-  MOZ_ASSERT(value != isCleanupJobActive());
-  setReservedSlot(IsCleanupJobActiveSlot, BooleanValue(value));
-}
-
 // FinalizationRegistry.prototype.register(target, heldValue [, unregisterToken
 // ])
 // https://tc39.es/proposal-weakrefs/#sec-finalization-registry.prototype.register
@@ -705,11 +695,7 @@ bool FinalizationRegistryObject::cleanupSome(JSContext* cx, unsigned argc,
   CallArgs args = CallArgsFromVp(argc, vp);
 
   // 1. Let finalizationRegistry be the this value.
-  // 2. If Type(finalizationRegistry) is not Object, throw a TypeError
-  //    exception.
-  // 3. If finalizationRegistry does not have [[Cells]] and
-  //    [[IsFinalizationRegistryCleanupJobActive]] internal slots, throw a
-  //    TypeError exception.
+  // 2. Perform ? RequireInternalSlot(finalizationRegistry, [[Cells]]).
   if (!args.thisv().isObject() ||
       !args.thisv().toObject().is<FinalizationRegistryObject>()) {
     JS_ReportErrorNumberASCII(
@@ -718,17 +704,10 @@ bool FinalizationRegistryObject::cleanupSome(JSContext* cx, unsigned argc,
     return false;
   }
 
-  // 4. If finalizationRegistry.[[IsFinalizationRegistryCleanupJobActive]] is
-  //    true, throw a TypeError exception.
   RootedFinalizationRegistryObject registry(
       cx, &args.thisv().toObject().as<FinalizationRegistryObject>());
-  if (registry->isCleanupJobActive()) {
-    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
-                              JSMSG_BAD_CLEANUP_STATE);
-    return false;
-  }
 
-  // 5. If callback is not undefined and IsCallable(callback) is false, throw a
+  // 3. If callback is not undefined and IsCallable(callback) is false, throw a
   //    TypeError exception.
   RootedObject cleanupCallback(cx);
   if (!args.get(0).isUndefined()) {
@@ -746,24 +725,6 @@ bool FinalizationRegistryObject::cleanupSome(JSContext* cx, unsigned argc,
   return true;
 }
 
-/* static */
-bool FinalizationRegistryObject::hasRegisteredRecordsToBeCleanedUp(
-    HandleFinalizationRegistryObject registry) {
-  FinalizationRecordVector* records = registry->recordsToBeCleanedUp();
-  size_t initialLength = records->length();
-  if (initialLength == 0) {
-    return false;
-  }
-
-  for (FinalizationRecordObject* record : *records) {
-    if (record->isActive()) {
-      return true;
-    }
-  }
-
-  return false;
-}
-
 // CleanupFinalizationRegistry ( finalizationRegistry [ , callback ] )
 // https://tc39.es/proposal-weakrefs/#sec-cleanup-finalization-registry
 /* static */
@@ -772,20 +733,7 @@ bool FinalizationRegistryObject::cleanupQueuedRecords(
     HandleObject callbackArg) {
   MOZ_ASSERT(cx->compartment() == registry->compartment());
 
-  // 2. If CheckForEmptyCells(finalizationRegistry) is false, return.
-  if (!hasRegisteredRecordsToBeCleanedUp(registry)) {
-    return true;
-  }
-
-  // 3. Let iterator be
-  //    !CreateFinalizationRegistryCleanupIterator(finalizationRegistry).
-  Rooted<FinalizationIteratorObject*> iterator(
-      cx, FinalizationIteratorObject::create(cx, registry));
-  if (!iterator) {
-    return false;
-  }
-
-  // 4. If callback is undefined, set callback to
+  // 2. If callback is undefined, set callback to
   //    finalizationRegistry.[[CleanupCallback]].
   RootedValue callback(cx);
   if (callbackArg) {
@@ -796,193 +744,34 @@ bool FinalizationRegistryObject::cleanupQueuedRecords(
     callback.setObject(*cleanupCallback);
   }
 
-  // 5. Set finalizationRegistry.[[IsFinalizationRegistryCleanupJobActive]] to
-  //    true.
-  registry->setCleanupJobActive(true);
-
-  FinalizationRecordVector* records = registry->recordsToBeCleanedUp();
-#ifdef DEBUG
-  size_t initialLength = records->length();
-#endif
-
-  // 6. Let result be Call(callback, undefined, iterator).
-  RootedValue iteratorVal(cx, ObjectValue(*iterator));
-  RootedValue rval(cx);
-  bool ok = Call(cx, callback, UndefinedHandleValue, iteratorVal, &rval);
-
-  // Remove records that were iterated over.
-  size_t index = iterator->index();
-  MOZ_ASSERT(index <= records->length());
-  MOZ_ASSERT(initialLength <= records->length());
-  if (index > 0) {
-    records->erase(records->begin(), records->begin() + index);
-  }
-
-  // 7. Set finalizationRegistry.[[IsFinalizationRegistryCleanupJobActive]] to
-  //    false.
-  registry->setCleanupJobActive(false);
-
-  // 8. Set iterator.[[FinalizationRegistry]] to empty.
-  iterator->clearFinalizationRegistry();
-
-  return ok;
-}
-
-///////////////////////////////////////////////////////////////////////////
-// FinalizationIteratorObject
-
-const JSClass FinalizationIteratorObject::class_ = {
-    "FinalizationRegistryCleanupIterator",
-    JSCLASS_HAS_RESERVED_SLOTS(SlotCount), JS_NULL_CLASS_OPS,
-    JS_NULL_CLASS_SPEC};
-
-const JSFunctionSpec FinalizationIteratorObject::methods_[] = {
-    JS_FN(js_next_str, next, 0, 0), JS_FS_END};
-
-const JSPropertySpec FinalizationIteratorObject::properties_[] = {
-    JS_STRING_SYM_PS(toStringTag, "FinalizationRegistry Cleanup Iterator",
-                     JSPROP_READONLY),
-    JS_PS_END};
-
-/* static */
-bool GlobalObject::initFinalizationIteratorProto(JSContext* cx,
-                                                 Handle<GlobalObject*> global) {
-  Rooted<JSObject*> base(
-      cx, GlobalObject::getOrCreateIteratorPrototype(cx, global));
-  if (!base) {
-    return false;
-  }
-  RootedPlainObject proto(
-      cx, GlobalObject::createBlankPrototypeInheriting<PlainObject>(cx, base));
-  if (!proto) {
-    return false;
-  }
-  if (!JS_DefineFunctions(cx, proto, FinalizationIteratorObject::methods_) ||
-      !JS_DefineProperties(cx, proto,
-                           FinalizationIteratorObject::properties_)) {
-    return false;
-  }
-  global->setReservedSlot(FINALIZATION_ITERATOR_PROTO, ObjectValue(*proto));
-  return true;
-}
-
-/* static */ FinalizationIteratorObject* FinalizationIteratorObject::create(
-    JSContext* cx, HandleFinalizationRegistryObject registry) {
-  MOZ_ASSERT(registry);
-
-  RootedObject proto(cx, GlobalObject::getOrCreateFinalizationIteratorPrototype(
-                             cx, cx->global()));
-  if (!proto) {
-    return nullptr;
-  }
-
-  FinalizationIteratorObject* iterator =
-      NewObjectWithGivenProto<FinalizationIteratorObject>(cx, proto);
-  if (!iterator) {
-    return nullptr;
-  }
-
-  iterator->initReservedSlot(FinalizationRegistrySlot, ObjectValue(*registry));
-  iterator->initReservedSlot(IndexSlot, Int32Value(0));
-
-  return iterator;
-}
-
-FinalizationRegistryObject* FinalizationIteratorObject::finalizationRegistry()
-    const {
-  Value value = getReservedSlot(FinalizationRegistrySlot);
-  if (value.isUndefined()) {
-    return nullptr;
-  }
-  return &value.toObject().as<FinalizationRegistryObject>();
-}
-
-size_t FinalizationIteratorObject::index() const {
-  int32_t i = getReservedSlot(IndexSlot).toInt32();
-  MOZ_ASSERT(i >= 0);
-  return size_t(i);
-}
-
-void FinalizationIteratorObject::setIndex(size_t i) {
-  MOZ_ASSERT(i <= INT32_MAX);
-  setReservedSlot(IndexSlot, Int32Value(int32_t(i)));
-}
-
-void FinalizationIteratorObject::clearFinalizationRegistry() {
-  MOZ_ASSERT(finalizationRegistry());
-  setReservedSlot(FinalizationRegistrySlot, UndefinedValue());
-}
-
-// %FinalizationRegistryCleanupIteratorPrototype%.next()
-// https://tc39.es/proposal-weakrefs/#sec-%finalizationregistrycleanupiterator%.next
-/* static */
-bool FinalizationIteratorObject::next(JSContext* cx, unsigned argc, Value* vp) {
-  CallArgs args = CallArgsFromVp(argc, vp);
-
-  // 1. Let iterator be the this value.
-  // 2. If Type(iterator) is not Object, throw a TypeError exception.
-  // 3. If iterator does not have a [[FinalizationRegistry]] internal slot,
-  //    throw a TypeError exception.
-  if (!args.thisv().isObject() ||
-      !args.thisv().toObject().is<FinalizationIteratorObject>()) {
-    JS_ReportErrorNumberASCII(
-        cx, GetErrorMessage, nullptr, JSMSG_NOT_A_FINALIZATION_ITERATOR,
-        "Receiver of FinalizationRegistryCleanupIterator.next call");
-    return false;
-  }
-
-  RootedFinalizationIteratorObject iterator(
-      cx, &args.thisv().toObject().as<FinalizationIteratorObject>());
-
-  // 4. If iterator.[[FinalizationRegistry]] is empty, throw a TypeError
-  //    exception.
-  // 5. Let finalizationRegistry be iterator.[[FinalizationRegistry]].
-  RootedFinalizationRegistryObject registry(cx,
-                                            iterator->finalizationRegistry());
-  if (!registry) {
-    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
-                              JSMSG_STALE_FINALIZATION_REGISTRY_ITERATOR);
-    return false;
-  }
-
-  // 8. If finalizationRegistry.[[Cells]] contains a Record cell such that
-  //    cell.[[Target]] is empty,
+  // 3. While finalizationRegistry.[[Cells]] contains a Record cell such that
+  //    cell.[[WeakRefTarget]] is empty, then an implementation may perform the
+  //    following steps,
   //    a. Choose any such cell.
   //    b. Remove cell from finalizationRegistry.[[Cells]].
-  //    c. Return CreateIterResultObject(cell.[[HeldValue]], false).
-  FinalizationRecordVector* records = registry->recordsToBeCleanedUp();
-  size_t index = iterator->index();
-  MOZ_ASSERT(index <= records->length());
+  //    c. Perform ? Call(callback, undefined, « cell.[[HeldValue]] »).
 
-  // Advance until we find a record that hasn't been unregistered.
-  while (index < records->length() && index < INT32_MAX &&
-         !(*records)[index]->isActive()) {
-    index++;
-    iterator->setIndex(index);
-  }
+  RootedValue heldValue(cx);
+  RootedValue rval(cx);
+  FinalizationRecordVector* records = registry->recordsToBeCleanedUp();
+  FinalizationRecordSet* activeRecords = registry->activeRecords();
+  while (!records->empty()) {
+    FinalizationRecordObject* record = records->popCopy();
 
-  if (index < records->length() && index < INT32_MAX) {
-    RootedFinalizationRecordObject record(cx, (*records)[index]);
-    RootedValue heldValue(cx, record->heldValue());
-    PlainObject* result = CreateIterResultObject(cx, heldValue, false);
-    if (!result) {
-      return false;
+    // Skip over records that have been unregistered.
+    if (!record->isActive()) {
+      continue;
     }
 
-    registry->activeRecords()->remove(record);
-    record->clear();
-    iterator->setIndex(index + 1);
+    heldValue.set(record->heldValue());
 
-    args.rval().setObject(*result);
-    return true;
-  }
+    activeRecords->remove(record);
+    record->clear();
 
-  // 9. Otherwise, return CreateIterResultObject(undefined, true).
-  PlainObject* result = CreateIterResultObject(cx, UndefinedHandleValue, true);
-  if (!result) {
-    return false;
+    if (!Call(cx, callback, UndefinedHandleValue, heldValue, &rval)) {
+      return false;
+    }
   }
 
-  args.rval().setObject(*result);
   return true;
 }
diff --git a/js/src/builtin/FinalizationRegistryObject.h b/js/src/builtin/FinalizationRegistryObject.h
index 926862a6cecb3..b9dbc05992955 100644
--- a/js/src/builtin/FinalizationRegistryObject.h
+++ b/js/src/builtin/FinalizationRegistryObject.h
@@ -181,7 +181,6 @@ class FinalizationRegistryObject : public NativeObject {
     ActiveRecords,
     RecordsToBeCleanedUpSlot,
     IsQueuedForCleanupSlot,
-    IsCleanupJobActiveSlot,
     SlotCount
   };
 
@@ -194,11 +193,9 @@ class FinalizationRegistryObject : public NativeObject {
   FinalizationRecordSet* activeRecords() const;
   FinalizationRecordVector* recordsToBeCleanedUp() const;
   bool isQueuedForCleanup() const;
-  bool isCleanupJobActive() const;
 
   void queueRecordToBeCleanedUp(FinalizationRecordObject* record);
   void setQueuedForCleanup(bool value);
-  void setCleanupJobActive(bool value);
 
   void sweep();
 
@@ -227,9 +224,6 @@ class FinalizationRegistryObject : public NativeObject {
 
   static void trace(JSTracer* trc, JSObject* obj);
   static void finalize(JSFreeOp* fop, JSObject* obj);
-
-  static bool hasRegisteredRecordsToBeCleanedUp(
-      HandleFinalizationRegistryObject registry);
 };
 
 // An iterator over a finalization registry's queued held values. In the spec
diff --git a/js/src/jit-test/tests/gc/bug-1620196.js b/js/src/jit-test/tests/gc/bug-1620196.js
index 2d145a1870929..79f98e073e894 100644
--- a/js/src/jit-test/tests/gc/bug-1620196.js
+++ b/js/src/jit-test/tests/gc/bug-1620196.js
@@ -2,8 +2,8 @@
 
 gczeal(4);
 let heldValues = [];
-registry = new FinalizationRegistry(iterator => {
-    heldValues.push(...iterator);
+registry = new FinalizationRegistry(value => {
+    heldValues.push(value);
 });
 registry.register({}, 42);
 gc();
diff --git a/js/src/jit-test/tests/gc/bug1600488-1.js b/js/src/jit-test/tests/gc/bug1600488-1.js
index 7827ec5baca03..b15bb2f2912c0 100644
--- a/js/src/jit-test/tests/gc/bug1600488-1.js
+++ b/js/src/jit-test/tests/gc/bug1600488-1.js
@@ -1,9 +1,9 @@
 // |jit-test| --enable-weak-refs
 
 const token = {};
-let iterated;
-const finalizationRegistry = new FinalizationRegistry(items => {
-    iterated = items.next().value;
+let cleanedUpValue;
+const finalizationRegistry = new FinalizationRegistry(value => {
+  cleanedUpValue = value;
 });
 {
     let object = {};
@@ -12,5 +12,5 @@ const finalizationRegistry = new FinalizationRegistry(items => {
 }
 gc();
 finalizationRegistry.cleanupSome();
-assertEq(iterated, token);
+assertEq(cleanedUpValue, token);
 assertEq(finalizationRegistry.unregister(token), false);
diff --git a/js/src/jit-test/tests/gc/finalizationRegistry-ccw.js b/js/src/jit-test/tests/gc/finalizationRegistry-ccw.js
index 12517b132b384..da4faffc40375 100644
--- a/js/src/jit-test/tests/gc/finalizationRegistry-ccw.js
+++ b/js/src/jit-test/tests/gc/finalizationRegistry-ccw.js
@@ -11,8 +11,8 @@ function ccwToObject() {
 }
 
 function newRegistry() {
-  return new FinalizationRegistry(iterator => {
-    heldValues.push(...iterator);
+  return new FinalizationRegistry(value => {
+    heldValues.push(value);
   });
 }
 
@@ -20,7 +20,7 @@ function ccwToRegistry() {
   let global = newGlobal({newCompartment: true});
   global.heldValues = heldValues;
   return global.eval(
-    `new FinalizationRegistry(iterator => heldValues.push(...iterator))`);
+    `new FinalizationRegistry(value => heldValues.push(value))`);
 }
 
 function incrementalGC() {
diff --git a/js/src/jit-test/tests/gc/finalizationRegistry-cleanupSome-recursive.js b/js/src/jit-test/tests/gc/finalizationRegistry-cleanupSome-recursive.js
new file mode 100644
index 0000000000000..2f38b8b899d79
--- /dev/null
+++ b/js/src/jit-test/tests/gc/finalizationRegistry-cleanupSome-recursive.js
@@ -0,0 +1,51 @@
+// |jit-test| --enable-weak-refs
+
+// Test trying to call cleanupSome recursively in callback.
+
+// 0: Initial state.
+// 1: Attempt recursive calls.
+// 2: After recursive calls.
+let state = 0;
+
+let registry = new FinalizationRegistry(x => {
+  if (state === 0) {
+    state = 1;
+    try {
+      registry.cleanupSome();
+    } catch (e) {
+      // Pass the test if any error was thrown.
+      return;
+    } finally {
+      state = 2;
+    }
+    throw new Error("expected stack overflow error");
+  }
+
+  if (state === 1) {
+    registry.cleanupSome();
+  }
+});
+
+// Attempt to find the maximum supported stack depth.
+function findStackSize(i) {
+  try {
+    return findStackSize(i + 1);
+  } catch {
+    return i;
+  }
+}
+const stackSize = findStackSize(0);
+
+// Multiply the calculated stack size by some factor just to be on the safe side.
+const exceedStackDepthLimit = stackSize * 5;
+
+let values = [];
+for (let i = 0; i < exceedStackDepthLimit; ++i) {
+  let v = {};
+  registry.register(v, i);
+  values.push(v);
+}
+values.length = 0;
+
+gc();
+drainJobQueue();
diff --git a/js/src/jit-test/tests/gc/finalizationRegistry-gray.js b/js/src/jit-test/tests/gc/finalizationRegistry-gray.js
index 1acdece8b6e5b..0746ad07cda42 100644
--- a/js/src/jit-test/tests/gc/finalizationRegistry-gray.js
+++ b/js/src/jit-test/tests/gc/finalizationRegistry-gray.js
@@ -2,7 +2,7 @@
 
 // Test gray finalization registry is correctly barrired.
 target = {};
-registry = new FinalizationRegistry(iterator => undefined);
+registry = new FinalizationRegistry(value => undefined);
 registry.register(target, 1);
 grayRoot()[0] = registry;
 registry = undefined;
diff --git a/js/src/jit-test/tests/gc/finalizationRegistry.js b/js/src/jit-test/tests/gc/finalizationRegistry.js
index c4af5a3c4e5e3..740c102ec5dd8 100644
--- a/js/src/jit-test/tests/gc/finalizationRegistry.js
+++ b/js/src/jit-test/tests/gc/finalizationRegistry.js
@@ -61,36 +61,9 @@ let registry = new FinalizationRegistry(x => 0);
 assertEq(Object.getPrototypeOf(registry), proto);
 assertEq(Object.getOwnPropertyNames(registry).length, 0);
 
-// Get a cleanup iterator.
-let iterator;
-registry = new FinalizationRegistry(it => iterator = it);
-registry.register({}, 0);
-gc();
-drainJobQueue();
-assertEq(typeof registry, 'object');
-assertEq(typeof iterator, 'object');
-
-// 3.5.2 The %FinalizationRegistryCleanupIteratorPrototype% Object
-let arrayIterator = [][Symbol.iterator]();
-let iteratorProto = arrayIterator.__proto__.__proto__;
-proto = iterator.__proto__;
-assertEq(typeof proto, "object");
-assertEq(proto.__proto__, iteratorProto);
-
-// 3.5.2.1 %FinalizationRegistryCleanupIteratorPrototype%.next()
-assertEq(proto.hasOwnProperty("next"), true);
-assertEq(typeof proto.next, "function");
-
-// 3.5.2.2 %FinalizationRegistryCleanupIteratorPrototype% [ @@toStringTag ]
-assertEq(proto[Symbol.toStringTag], "FinalizationRegistry Cleanup Iterator");
-checkPropertyDescriptor(proto, Symbol.toStringTag, false, false, true);
-
-// 3.5.3 Properties of FinalizationRegistry Cleanup Iterator Instances
-assertEq(Object.getOwnPropertyNames(iterator).length, 0);
-
 let heldValues = [];
-registry = new FinalizationRegistry(iterator => {
-  heldValues.push(...iterator);
+registry = new FinalizationRegistry(value => {
+  heldValues.push(value);
 });
 
 // Test a single target.
@@ -117,8 +90,8 @@ for (let i = 0; i < 100; i++) {
 // Test a single object in multiple registries
 heldValues = [];
 let heldValues2 = [];
-let registry2 = new FinalizationRegistry(iterator => {
-  heldValues2.push(...iterator);
+let registry2 = new FinalizationRegistry(value => {
+  heldValues2.push(value);
 });
 {
   let object = {};
@@ -196,8 +169,8 @@ class MyRegistry extends FinalizationRegistry {
     super(callback);
   }
 }
-let r2 = new MyRegistry(iterator => {
-  heldValues.push(...iterator);
+let r2 = new MyRegistry(value => {
+  heldValues.push(value);
 });
 heldValues = [];
 r2.register({}, 42);
@@ -206,26 +179,9 @@ drainJobQueue();
 assertEq(heldValues.length, 1);
 assertEq(heldValues[0], 42);
 
-// Test trying to use iterator after the callback.
-iterator = undefined;
-let r3 = new FinalizationRegistry(i => iterator = i);
-r3.register({}, 1);
-gc();
-drainJobQueue();
-assertEq(typeof iterator, 'object');
-assertThrowsTypeError(() => iterator.next());
-
-// Test trying to use the wrong iterator inside the callback.
-let r4 = new FinalizationRegistry(x => {
-  assertThrowsTypeError(() => iterator.next());
-});
-r4.register({}, 1);
-gc();
-drainJobQueue();
-
 // Test cleanupSome.
 heldValues = [];
-let r5 = new FinalizationRegistry(i => heldValues = [...i]);
+let r5 = new FinalizationRegistry(v => heldValues.push(v));
 r5.register({}, 1);
 r5.register({}, 2);
 r5.register({}, 3);
@@ -239,15 +195,29 @@ assertEq(heldValues[2], 3);
 
 // Test trying to call cleanupSome in callback.
 let r6 = new FinalizationRegistry(x => {
-  assertThrowsTypeError(() => r6.cleanupSome());
+  r6.cleanupSome();
 });
 r6.register({}, 1);
 gc();
 drainJobQueue();
 
+// Test trying to call cleanupSome in callback with multiple values.
+let callbackCounter7 = 0;
+let r7 = new FinalizationRegistry(x => {
+  callbackCounter7++;
+  r7.cleanupSome();
+});
+r7.register({}, 1);
+r7.register({}, 2);
+r7.register({}, 3);
+r7.register({}, 4);
+gc();
+drainJobQueue();
+assertEq(callbackCounter7, 4);
+
 // Test that targets don't keep the finalization registry alive.
 let target = {};
-registry = new FinalizationRegistry(iterator => undefined);
+registry = new FinalizationRegistry(value => undefined);
 registry.register(target, 1);
 let weakRef = new WeakRef(registry);
 registry = undefined;
@@ -259,7 +229,7 @@ assertEq(typeof target, 'object');
 
 // Test that targets don't keep the finalization registry alive when also
 // used as the unregister token.
-registry = new FinalizationRegistry(iterator => undefined);
+registry = new FinalizationRegistry(value => undefined);
 registry.register(target, 1, target);
 weakRef = new WeakRef(registry);
 registry = undefined;
@@ -271,8 +241,8 @@ assertEq(typeof target, 'object');
 
 // Test that cleanup doesn't happen if the finalization registry dies.
 heldValues = [];
-new FinalizationRegistry(iterator => {
-  heldValues.push(...iterator);
+new FinalizationRegistry(value => {
+  heldValues.push(value);
 }).register({}, 1);
 gc();
 drainJobQueue();
diff --git a/js/src/tests/jstests.list b/js/src/tests/jstests.list
index 1ae5295bd5f38..afdd45ab53927 100644
--- a/js/src/tests/jstests.list
+++ b/js/src/tests/jstests.list
@@ -412,14 +412,6 @@ skip script test262/intl402/ListFormat/constructor/constructor/proto-from-ctor-r
 # https://bugzilla.mozilla.org/show_bug.cgi?id=1362154
 skip script test262/built-ins/String/prototype/replaceAll/searchValue-replacer-RegExp-call.js
 
-# https://github.com/tc39/proposal-weakrefs/pull/187
-# https://bugzilla.mozilla.org/show_bug.cgi?id=1629796
-skip script test262/built-ins/FinalizationRegistry/gc-has-one-chance-to-call-cleanupCallback.js
-skip script test262/built-ins/FinalizationRegistry/prototype/cleanupSome/holdings-multiple-values.js
-skip script test262/built-ins/FinalizationRegistry/prototype/cleanupSome/cleanup-prevented-with-reference.js
-skip script test262/built-ins/FinalizationRegistry/prototype/cleanupSome/reentrancy.js
-skip script test262/built-ins/FinalizationRegistry/prototype/unregister/unregister-cleaned-up-cell.js
-
 # Depends upon the SharedArrayBuffer constructor being defined as a global
 # property -- and right now, it's only defined for cross-site-isolated pages
 # that request it using COOP/COEP.
diff --git a/js/src/vm/GlobalObject.h b/js/src/vm/GlobalObject.h
index 35a0b6872cce5..b708c67aa6f58 100644
--- a/js/src/vm/GlobalObject.h
+++ b/js/src/vm/GlobalObject.h
@@ -115,7 +115,6 @@ class GlobalObject : public NativeObject {
     IMPORT_ENTRY_PROTO,
     EXPORT_ENTRY_PROTO,
     REQUESTED_MODULE_PROTO,
-    FINALIZATION_ITERATOR_PROTO,
     REGEXP_STATICS,
     RUNTIME_CODEGEN_ENABLED,
     INTRINSICS,
@@ -548,12 +547,6 @@ class GlobalObject : public NativeObject {
     return &global->getPrototype(JSProto_TypedArray).toObject();
   }
 
-  static JSObject* getOrCreateFinalizationIteratorPrototype(
-      JSContext* cx, Handle<GlobalObject*> global) {
-    return getOrCreateObject(cx, global, FINALIZATION_ITERATOR_PROTO,
-                             initFinalizationIteratorProto);
-  }
-
  private:
   using ObjectInitOp = bool (*)(JSContext*, Handle<GlobalObject*>);
 
@@ -853,10 +846,6 @@ class GlobalObject : public NativeObject {
   static bool initTypedObjectModule(JSContext* cx,
                                     Handle<GlobalObject*> global);
 
-  // Implemented in builtin/FinalizationRegistry.cpp
-  static bool initFinalizationIteratorProto(JSContext* cx,
-                                            Handle<GlobalObject*> global);
-
   static bool initStandardClasses(JSContext* cx, Handle<GlobalObject*> global);
   static bool initSelfHostingBuiltins(JSContext* cx,
                                       Handle<GlobalObject*> global,
diff --git a/js/xpconnect/tests/mochitest/finalizationRegistry_worker.js b/js/xpconnect/tests/mochitest/finalizationRegistry_worker.js
index 8b2233c268930..d603cdab38002 100644
--- a/js/xpconnect/tests/mochitest/finalizationRegistry_worker.js
+++ b/js/xpconnect/tests/mochitest/finalizationRegistry_worker.js
@@ -19,27 +19,27 @@ onmessage = (event) => {
 
 function startTest() {
   // Registry with no registered objects.
-  let registry1 = new FinalizationRegistry(i => holdings1 = [...i]);
+  let registry1 = new FinalizationRegistry(v => { holdings1.push(v); });
 
   // Registry with three registered objects.
-  let registry2 = new FinalizationRegistry(i => holdings2 = [...i]);
+  let registry2 = new FinalizationRegistry(v => { holdings2.push(v); });
   registry2.register({}, 1);
   registry2.register({}, 2);
   registry2.register({}, 3);
 
   // Registry with registered object that is then unregistered.
-  let registry3 = new FinalizationRegistry(i => holdings3 = [...i]);
+  let registry3 = new FinalizationRegistry(v => { holdings3.push(v); });
   let token3 = {}
   registry3.register({}, 1, token3);
   registry3.unregister(token3);
 
   // Registry with registered object that doesn't die.
-  let registry4 = new FinalizationRegistry(i => holdings4 = [...i]);
+  let registry4 = new FinalizationRegistry(v => { holdings4.push(v); });
   let object4 = {};
   registry4.register(object4, 1);
 
   // Registry observing cyclic JS data structure.
-  let registry5 = new FinalizationRegistry(i => holdings5 = [...i]);
+  let registry5 = new FinalizationRegistry(v => { holdings5.push(v); });
   registry5.register(makeJSCycle(4), 5);
 
   const { gc } = getJSTestingFunctions();
diff --git a/js/xpconnect/tests/mochitest/test_finalizationRegistry.html b/js/xpconnect/tests/mochitest/test_finalizationRegistry.html
index db9ddef14c902..dea4e39c4a4ac 100644
--- a/js/xpconnect/tests/mochitest/test_finalizationRegistry.html
+++ b/js/xpconnect/tests/mochitest/test_finalizationRegistry.html
@@ -12,35 +12,35 @@
 
         // Registry with no registered objects.
         let holdings1 = [];
-        let registry1 = new FinalizationRegistry(i => holdings1 = [...i]);
+        let registry1 = new FinalizationRegistry(v => { holdings1.push(v); });
 
         // Registry with three registered objects.
         let holdings2 = [];
-        let registry2 = new FinalizationRegistry(i => holdings2 = [...i]);
+        let registry2 = new FinalizationRegistry(v => { holdings2.push(v); });
         registry2.register({}, 1);
         registry2.register({}, 2);
         registry2.register({}, 3);
 
         // Registry with registered object that is then unregistered.
         let holdings3 = [];
-        let registry3 = new FinalizationRegistry(i => holdings3 = [...i]);
+        let registry3 = new FinalizationRegistry(v => { holdings3.push(v); });
         let token3 = {}
         registry3.register({}, 1, token3);
         registry3.unregister(token3);
 
         // Registry with registered object that doesn't die.
         let holdings4 = [];
-        let registry4 = new FinalizationRegistry(i => holdings4 = [...i]);
+        let registry4 = new FinalizationRegistry(v => { holdings4.push(v); });
         registry4.register(object4, 1);
 
         // Registry observing cyclic JS data structure.
         let holdings5 = [];
-        let registry5 = new FinalizationRegistry(i => holdings5 = [...i]);
+        let registry5 = new FinalizationRegistry(v => { holdings5.push(v); });
         registry5.register(makeJSCycle(4), 5);
 
         // Registry observing cyclic DOM/JS data structure.
         let holdings6 = [];
-        let registry6 = new FinalizationRegistry(i => holdings6 = [...i]);
+        let registry6 = new FinalizationRegistry(v => { holdings6.push(v); });
         registry6.register(makeDOMCycle(4), 6);
 
         // Need to run full GC/CC/GC cycle to collect cyclic garbage through DOM