diff --git a/dom/bindings/Codegen.py b/dom/bindings/Codegen.py
index 758cf62369cb..518ce18a3567 100644
--- a/dom/bindings/Codegen.py
+++ b/dom/bindings/Codegen.py
@@ -476,6 +476,7 @@ class CGDOMJSClass(CGThing):
                 nullptr,               /* setProperty */
                 ${enumerate}, /* enumerate */
                 ${resolve}, /* resolve */
+                nullptr,               /* mayResolve */
                 nullptr,               /* convert */
                 ${finalize}, /* finalize */
                 ${call}, /* call */
@@ -616,6 +617,7 @@ class CGPrototypeJSClass(CGThing):
                 nullptr,               /* setProperty */
                 nullptr,               /* enumerate */
                 nullptr,               /* resolve */
+                nullptr,               /* mayResolve */
                 nullptr,               /* convert */
                 nullptr,               /* finalize */
                 nullptr,               /* call */
@@ -709,6 +711,7 @@ class CGInterfaceObjectJSClass(CGThing):
                 nullptr,               /* setProperty */
                 nullptr,               /* enumerate */
                 nullptr,               /* resolve */
+                nullptr,               /* mayResolve */
                 nullptr,               /* convert */
                 nullptr,               /* finalize */
                 ${ctorname}, /* call */
diff --git a/dom/indexedDB/ActorsParent.cpp b/dom/indexedDB/ActorsParent.cpp
index ad44a4eddb68..28eadab0766f 100644
--- a/dom/indexedDB/ActorsParent.cpp
+++ b/dom/indexedDB/ActorsParent.cpp
@@ -20125,6 +20125,7 @@ const JSClass CreateIndexOp::ThreadLocalJSRuntime::kGlobalClass = {
   /* setProperty */ nullptr,
   /* enumerate */ nullptr,
   /* resolve */ nullptr,
+  /* mayResolve */ nullptr,
   /* convert */ nullptr,
   /* finalize */ nullptr,
   /* call */ nullptr,
diff --git a/dom/plugins/base/nsJSNPRuntime.cpp b/dom/plugins/base/nsJSNPRuntime.cpp
index e796f24cce80..091aee752f8a 100644
--- a/dom/plugins/base/nsJSNPRuntime.cpp
+++ b/dom/plugins/base/nsJSNPRuntime.cpp
@@ -213,6 +213,7 @@ const static js::Class sNPObjectJSWrapperClass =
     NPObjWrapper_SetProperty,
     nullptr,
     NPObjWrapper_Resolve,
+    nullptr,                                                /* mayResolve */
     NPObjWrapper_Convert,
     NPObjWrapper_Finalize,
     NPObjWrapper_Call,
@@ -265,7 +266,7 @@ static const JSClass sNPObjectMemberClass =
   {
     "NPObject Ambiguous Member class", JSCLASS_HAS_PRIVATE | JSCLASS_IMPLEMENTS_BARRIERS,
     nullptr, nullptr, nullptr, nullptr,
-    nullptr, nullptr, NPObjectMember_Convert,
+    nullptr, nullptr, nullptr, NPObjectMember_Convert,
     NPObjectMember_Finalize, NPObjectMember_Call,
     nullptr, nullptr, NPObjectMember_Trace
   };
diff --git a/dom/workers/WorkerScope.cpp b/dom/workers/WorkerScope.cpp
index bb1e3e9ee291..0ee3106b8fc7 100644
--- a/dom/workers/WorkerScope.cpp
+++ b/dom/workers/WorkerScope.cpp
@@ -599,6 +599,7 @@ const js::Class workerdebuggersandbox_class = {
     nullptr,
     workerdebuggersandbox_enumerate,
     workerdebuggersandbox_resolve,
+    nullptr, /* mayResolve */
     workerdebuggersandbox_convert,
     workerdebuggersandbox_finalize,
     nullptr,
diff --git a/dom/xbl/nsXBLBinding.cpp b/dom/xbl/nsXBLBinding.cpp
index 274ed388ba62..1bb0eb8d9d94 100644
--- a/dom/xbl/nsXBLBinding.cpp
+++ b/dom/xbl/nsXBLBinding.cpp
@@ -93,7 +93,7 @@ static const JSClass gPrototypeJSClass = {
     // Our one reserved slot holds the relevant nsXBLPrototypeBinding
     JSCLASS_HAS_RESERVED_SLOTS(1),
     nullptr, nullptr, nullptr, nullptr,
-    XBLEnumerate, nullptr,
+    XBLEnumerate, nullptr, nullptr,
     nullptr, XBLFinalize,
     nullptr, nullptr, nullptr, nullptr
 };
diff --git a/js/public/Class.h b/js/public/Class.h
index cdcc760b6be5..34af88671f4d 100644
--- a/js/public/Class.h
+++ b/js/public/Class.h
@@ -24,6 +24,7 @@
  * object behavior and, e.g., allows custom slow layout.
  */
 
+struct JSAtomState;
 struct JSFreeOp;
 struct JSFunctionSpec;
 
@@ -281,6 +282,18 @@ typedef bool
 (* JSResolveOp)(JSContext* cx, JS::HandleObject obj, JS::HandleId id,
                 bool* resolvedp);
 
+// A class with a resolve hook can optionally have a mayResolve hook. This hook
+// must have no side effects and must return true for a given id if the resolve
+// hook may resolve this id. This is useful when we're doing a "pure" lookup: if
+// mayResolve returns false, we know we don't have to call the effectful resolve
+// hook.
+//
+// maybeObj, if non-null, is the object on which we're doing the lookup. This
+// can be nullptr: during JIT compilation we sometimes know the Class but not
+// the object.
+typedef bool
+(* JSMayResolveOp)(const JSAtomState& names, jsid id, JSObject* maybeObj);
+
 // Convert obj to the given type, returning true with the resulting value in
 // *vp on success, and returning false on error or exception.
 typedef bool
@@ -420,6 +433,7 @@ typedef void
     JSSetterOp          setProperty;                                          \
     JSEnumerateOp       enumerate;                                            \
     JSResolveOp         resolve;                                              \
+    JSMayResolveOp      mayResolve;                                           \
     JSConvertOp         convert;                                              \
     FinalizeOpType      finalize;                                             \
     JSNative            call;                                                 \
@@ -688,6 +702,8 @@ static_assert(offsetof(JSClass, enumerate) == offsetof(Class, enumerate),
               "Class and JSClass must be consistent");
 static_assert(offsetof(JSClass, resolve) == offsetof(Class, resolve),
               "Class and JSClass must be consistent");
+static_assert(offsetof(JSClass, mayResolve) == offsetof(Class, mayResolve),
+              "Class and JSClass must be consistent");
 static_assert(offsetof(JSClass, convert) == offsetof(Class, convert),
               "Class and JSClass must be consistent");
 static_assert(offsetof(JSClass, finalize) == offsetof(Class, finalize),
diff --git a/js/src/asmjs/AsmJSModule.cpp b/js/src/asmjs/AsmJSModule.cpp
index 3d45e892ce06..ecfb533d3c9a 100644
--- a/js/src/asmjs/AsmJSModule.cpp
+++ b/js/src/asmjs/AsmJSModule.cpp
@@ -998,6 +998,7 @@ const Class AsmJSModuleObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     AsmJSModuleObject_finalize,
     nullptr, /* call */
diff --git a/js/src/builtin/Intl.cpp b/js/src/builtin/Intl.cpp
index 08811268117b..dbc2c44cd25c 100644
--- a/js/src/builtin/Intl.cpp
+++ b/js/src/builtin/Intl.cpp
@@ -565,6 +565,7 @@ static const Class CollatorClass = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     collator_finalize
 };
@@ -1057,6 +1058,7 @@ static const Class NumberFormatClass = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     numberFormat_finalize
 };
@@ -1516,6 +1518,7 @@ static const Class DateTimeFormatClass = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     dateTimeFormat_finalize
 };
diff --git a/js/src/builtin/MapObject.cpp b/js/src/builtin/MapObject.cpp
index 2626b5923a55..358eb90f91dc 100644
--- a/js/src/builtin/MapObject.cpp
+++ b/js/src/builtin/MapObject.cpp
@@ -880,6 +880,7 @@ const Class MapIteratorObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     MapIteratorObject::finalize
 };
@@ -1024,6 +1025,7 @@ const Class MapObject::class_ = {
     nullptr, // setProperty
     nullptr, // enumerate
     nullptr, // resolve
+    nullptr, // mayResolve
     nullptr, // convert
     finalize,
     nullptr, // call
@@ -1616,6 +1618,7 @@ const Class SetIteratorObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     SetIteratorObject::finalize
 };
@@ -1756,6 +1759,7 @@ const Class SetObject::class_ = {
     nullptr, // setProperty
     nullptr, // enumerate
     nullptr, // resolve
+    nullptr, // mayResolve
     nullptr, // convert
     finalize,
     nullptr, // call
diff --git a/js/src/builtin/Object.cpp b/js/src/builtin/Object.cpp
index 6d3413c0c1b9..206b76ef8065 100644
--- a/js/src/builtin/Object.cpp
+++ b/js/src/builtin/Object.cpp
@@ -1189,6 +1189,7 @@ const Class PlainObject::class_ = {
     nullptr,  /* setProperty */
     nullptr,  /* enumerate */
     nullptr,  /* resolve */
+    nullptr,  /* mayResolve */
     nullptr,  /* convert */
     nullptr,  /* finalize */
     nullptr,  /* call */
diff --git a/js/src/builtin/SIMD.cpp b/js/src/builtin/SIMD.cpp
index 2ff61409f677..bf6674d66fbf 100644
--- a/js/src/builtin/SIMD.cpp
+++ b/js/src/builtin/SIMD.cpp
@@ -180,6 +180,7 @@ const Class SimdTypeDescr::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     TypeDescr::finalize,
     call
diff --git a/js/src/builtin/SymbolObject.cpp b/js/src/builtin/SymbolObject.cpp
index bb188b6d271f..f166df2626f7 100644
--- a/js/src/builtin/SymbolObject.cpp
+++ b/js/src/builtin/SymbolObject.cpp
@@ -25,6 +25,7 @@ const Class SymbolObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     convert
 };
 
diff --git a/js/src/builtin/TestingFunctions.cpp b/js/src/builtin/TestingFunctions.cpp
index a355cfef6c01..ba2cd99e80fc 100644
--- a/js/src/builtin/TestingFunctions.cpp
+++ b/js/src/builtin/TestingFunctions.cpp
@@ -1154,6 +1154,7 @@ static const JSClass FinalizeCounterClass = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     finalize_counter_finalize
 };
@@ -1835,6 +1836,7 @@ const Class CloneBufferObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     Finalize
 };
diff --git a/js/src/builtin/TypedObject.cpp b/js/src/builtin/TypedObject.cpp
index 8e1b9f21ab10..53120d7ec123 100644
--- a/js/src/builtin/TypedObject.cpp
+++ b/js/src/builtin/TypedObject.cpp
@@ -224,6 +224,7 @@ const Class js::ScalarTypeDescr::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     TypeDescr::finalize,
     ScalarTypeDescr::call
@@ -321,6 +322,7 @@ const Class js::ReferenceTypeDescr::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     TypeDescr::finalize,
     ReferenceTypeDescr::call
@@ -500,6 +502,7 @@ const Class ArrayTypeDescr::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     TypeDescr::finalize,
     nullptr, /* call */
@@ -727,6 +730,7 @@ const Class StructTypeDescr::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     TypeDescr::finalize,
     nullptr, /* call */
@@ -2246,6 +2250,7 @@ OutlineTransparentTypedObject::getOrCreateBuffer(JSContext* cx)
         nullptr,        /* setProperty */                \
         nullptr,        /* enumerate   */                \
         nullptr,        /* resolve     */                \
+        nullptr,        /* mayResolve  */                \
         nullptr,        /* convert     */                \
         nullptr,        /* finalize    */                \
         nullptr,        /* call        */                \
diff --git a/js/src/ctypes/CTypes.cpp b/js/src/ctypes/CTypes.cpp
index cd2d667a2f26..0249a2adc5c4 100644
--- a/js/src/ctypes/CTypes.cpp
+++ b/js/src/ctypes/CTypes.cpp
@@ -533,7 +533,7 @@ static const JSClass sCABIClass = {
 static const JSClass sCTypeProtoClass = {
   "CType",
   JSCLASS_HAS_RESERVED_SLOTS(CTYPEPROTO_SLOTS),
-  nullptr, nullptr, nullptr, nullptr,
+  nullptr, nullptr, nullptr, nullptr, nullptr,
   nullptr, nullptr, nullptr, nullptr,
   ConstructAbstract, nullptr, ConstructAbstract
 };
@@ -548,7 +548,7 @@ static const JSClass sCDataProtoClass = {
 static const JSClass sCTypeClass = {
   "CType",
   JSCLASS_IMPLEMENTS_BARRIERS | JSCLASS_HAS_RESERVED_SLOTS(CTYPE_SLOTS),
-  nullptr, nullptr, nullptr, nullptr,
+  nullptr, nullptr, nullptr, nullptr, nullptr,
   nullptr, nullptr, nullptr, CType::Finalize,
   CType::ConstructData, CType::HasInstance, CType::ConstructData,
   CType::Trace
@@ -558,14 +558,14 @@ static const JSClass sCDataClass = {
   "CData",
   JSCLASS_HAS_RESERVED_SLOTS(CDATA_SLOTS),
   nullptr, nullptr, ArrayType::Getter, ArrayType::Setter,
-  nullptr, nullptr, nullptr, CData::Finalize,
+  nullptr, nullptr, nullptr, nullptr, CData::Finalize,
   FunctionType::Call, nullptr, FunctionType::Call
 };
 
 static const JSClass sCClosureClass = {
   "CClosure",
   JSCLASS_IMPLEMENTS_BARRIERS | JSCLASS_HAS_RESERVED_SLOTS(CCLOSURE_SLOTS),
-  nullptr, nullptr, nullptr, nullptr,
+  nullptr, nullptr, nullptr, nullptr, nullptr,
   nullptr, nullptr, nullptr, CClosure::Finalize,
   nullptr, nullptr, nullptr, CClosure::Trace
 };
@@ -587,7 +587,7 @@ static const JSClass sCDataFinalizerProtoClass = {
 static const JSClass sCDataFinalizerClass = {
   "CDataFinalizer",
   JSCLASS_HAS_PRIVATE | JSCLASS_HAS_RESERVED_SLOTS(CDATAFINALIZER_SLOTS),
-  nullptr, nullptr, nullptr, nullptr,
+  nullptr, nullptr, nullptr, nullptr, nullptr,
   nullptr, nullptr, nullptr, CDataFinalizer::Finalize
 };
 
@@ -773,14 +773,14 @@ static const JSClass sUInt64ProtoClass = {
 static const JSClass sInt64Class = {
   "Int64",
   JSCLASS_HAS_RESERVED_SLOTS(INT64_SLOTS),
-  nullptr, nullptr, nullptr, nullptr,
+  nullptr, nullptr, nullptr, nullptr, nullptr,
   nullptr, nullptr, nullptr, Int64Base::Finalize
 };
 
 static const JSClass sUInt64Class = {
   "UInt64",
   JSCLASS_HAS_RESERVED_SLOTS(INT64_SLOTS),
-  nullptr, nullptr, nullptr, nullptr,
+  nullptr, nullptr, nullptr, nullptr, nullptr,
   nullptr, nullptr, nullptr, Int64Base::Finalize
 };
 
diff --git a/js/src/ctypes/Library.cpp b/js/src/ctypes/Library.cpp
index 688c8a03d836..394fa8a5882b 100644
--- a/js/src/ctypes/Library.cpp
+++ b/js/src/ctypes/Library.cpp
@@ -35,7 +35,7 @@ typedef Rooted<JSFlatString*>    RootedFlatString;
 static const JSClass sLibraryClass = {
   "Library",
   JSCLASS_HAS_RESERVED_SLOTS(LIBRARY_SLOTS),
-  nullptr, nullptr, nullptr, nullptr,
+  nullptr, nullptr, nullptr, nullptr, nullptr,
   nullptr, nullptr, nullptr, Library::Finalize
 };
 
diff --git a/js/src/gdb/gdb-tests.cpp b/js/src/gdb/gdb-tests.cpp
index 9ab81825c70d..ada42171ba77 100644
--- a/js/src/gdb/gdb-tests.cpp
+++ b/js/src/gdb/gdb-tests.cpp
@@ -17,7 +17,7 @@ const JSClass global_class = {
     "global", JSCLASS_GLOBAL_FLAGS,
     nullptr, nullptr, nullptr, nullptr,
     nullptr, nullptr, nullptr, nullptr,
-    nullptr, nullptr, nullptr,
+    nullptr, nullptr, nullptr, nullptr,
     JS_GlobalObjectTraceHook
 };
 
diff --git a/js/src/jit/IonBuilder.cpp b/js/src/jit/IonBuilder.cpp
index 00f6806c8a04..397eb88178f3 100644
--- a/js/src/jit/IonBuilder.cpp
+++ b/js/src/jit/IonBuilder.cpp
@@ -7102,18 +7102,8 @@ ObjectHasExtraOwnProperty(CompileCompartment* comp, TypeSet::ObjectKey* object,
         return name == comp->runtime()->names().length;
 
     // Resolve hooks can install new properties on objects on demand.
-    if (!clasp->resolve)
-        return false;
-
-    if (clasp->resolve == str_resolve) {
-        // str_resolve only resolves integers, not names.
-        return false;
-    }
-
-    if (clasp->resolve == fun_resolve)
-        return FunctionHasResolveHook(comp->runtime()->names(), NameToId(name));
-
-    return true;
+    JSObject* singleton = object->isSingleton() ? object->singleton() : nullptr;
+    return ClassMayResolveId(comp->runtime()->names(), clasp, NameToId(name), singleton);
 }
 
 void
diff --git a/js/src/jsapi-tests/testChromeBuffer.cpp b/js/src/jsapi-tests/testChromeBuffer.cpp
index 555598d41541..a7e94195229a 100644
--- a/js/src/jsapi-tests/testChromeBuffer.cpp
+++ b/js/src/jsapi-tests/testChromeBuffer.cpp
@@ -22,6 +22,7 @@ static const JSClass global_class = {
     nullptr,
     nullptr,
     nullptr,
+    nullptr,
     JS_GlobalObjectTraceHook
 };
 
diff --git a/js/src/jsapi-tests/testFreshGlobalEvalRedefinition.cpp b/js/src/jsapi-tests/testFreshGlobalEvalRedefinition.cpp
index 59f33c9d31df..0646de6a84c4 100644
--- a/js/src/jsapi-tests/testFreshGlobalEvalRedefinition.cpp
+++ b/js/src/jsapi-tests/testFreshGlobalEvalRedefinition.cpp
@@ -25,7 +25,7 @@ BEGIN_TEST(testRedefineGlobalEval)
         "global", JSCLASS_GLOBAL_FLAGS,
         nullptr, nullptr, nullptr, nullptr,
         GlobalEnumerate, GlobalResolve, nullptr,
-        nullptr, nullptr, nullptr, nullptr,
+        nullptr, nullptr, nullptr, nullptr, nullptr,
         JS_GlobalObjectTraceHook
     };
 
diff --git a/js/src/jsapi-tests/testGCNursery.cpp b/js/src/jsapi-tests/testGCNursery.cpp
index d7d2cea1fb40..db7276ac810f 100644
--- a/js/src/jsapi-tests/testGCNursery.cpp
+++ b/js/src/jsapi-tests/testGCNursery.cpp
@@ -27,6 +27,7 @@ static const js::Class TenuredClass = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* ??? */
     _finalize,
     nullptr, /* call */
@@ -47,6 +48,7 @@ static const js::Class NurseryClass = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* ??? */
     _finalize,
     nullptr, /* call */
diff --git a/js/src/jsapi-tests/testNewObject.cpp b/js/src/jsapi-tests/testNewObject.cpp
index f4da9bdfc13a..335c3736b8c2 100644
--- a/js/src/jsapi-tests/testNewObject.cpp
+++ b/js/src/jsapi-tests/testNewObject.cpp
@@ -98,7 +98,7 @@ BEGIN_TEST(testNewObject_1)
         0,
         nullptr, nullptr, nullptr, nullptr,
         nullptr, nullptr, nullptr, nullptr,
-        nullptr, nullptr, constructHook
+        nullptr, nullptr, nullptr, constructHook
     };
     JS::RootedObject ctor(cx, JS_NewObject(cx, &cls));
     CHECK(ctor);
diff --git a/js/src/jsapi-tests/testOps.cpp b/js/src/jsapi-tests/testOps.cpp
index f0072c2850f8..c3030f7c619c 100644
--- a/js/src/jsapi-tests/testOps.cpp
+++ b/js/src/jsapi-tests/testOps.cpp
@@ -23,7 +23,7 @@ static const JSClass myClass = {
     "MyClass",
     0,
     nullptr, nullptr, nullptr, nullptr,
-    nullptr, nullptr, my_convert
+    nullptr, nullptr, nullptr, my_convert
 };
 
 static bool
diff --git a/js/src/jsapi-tests/testPersistentRooted.cpp b/js/src/jsapi-tests/testPersistentRooted.cpp
index 3273ab8963f1..9b86e8dba038 100644
--- a/js/src/jsapi-tests/testPersistentRooted.cpp
+++ b/js/src/jsapi-tests/testPersistentRooted.cpp
@@ -29,6 +29,7 @@ const JSClass BarkWhenTracedClass::class_ = {
     nullptr,
     nullptr,
     nullptr,
+    nullptr,
     finalize,
     nullptr,
     nullptr,
diff --git a/js/src/jsapi-tests/testWeakMap.cpp b/js/src/jsapi-tests/testWeakMap.cpp
index 24861e59ec06..acb3b9487b58 100644
--- a/js/src/jsapi-tests/testWeakMap.cpp
+++ b/js/src/jsapi-tests/testWeakMap.cpp
@@ -148,6 +148,7 @@ JSObject* newKey()
         nullptr, /* setProperty */
         nullptr, /* enumerate */
         nullptr, /* resolve */
+        nullptr, /* mayResolve */
         nullptr, /* convert */
         nullptr, /* finalize */
         nullptr, /* call */
@@ -204,6 +205,7 @@ JSObject* newDelegate()
         nullptr, /* setProperty */
         nullptr, /* enumerate */
         nullptr, /* resolve */
+        nullptr, /* mayResolve */
         nullptr, /* convert */
         nullptr, /* finalize */
         nullptr, /* call */
diff --git a/js/src/jsapi-tests/tests.h b/js/src/jsapi-tests/tests.h
index a57a0b7b218b..d3423fea0572 100644
--- a/js/src/jsapi-tests/tests.h
+++ b/js/src/jsapi-tests/tests.h
@@ -230,7 +230,7 @@ class JSAPITest
             "global", JSCLASS_GLOBAL_FLAGS,
             nullptr, nullptr, nullptr, nullptr,
             nullptr, nullptr, nullptr, nullptr,
-            nullptr, nullptr, nullptr,
+            nullptr, nullptr, nullptr, nullptr,
             JS_GlobalObjectTraceHook
         };
         return &c;
diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index 83221f89435d..2bf2db2fd5eb 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -1138,13 +1138,12 @@ typedef struct JSStdName {
 } JSStdName;
 
 static const JSStdName*
-LookupStdName(JSRuntime* rt, HandleString name, const JSStdName* table)
+LookupStdName(const JSAtomState& names, JSAtom* name, const JSStdName* table)
 {
-    MOZ_ASSERT(name->isAtom());
     for (unsigned i = 0; !table[i].isSentinel(); i++) {
         if (table[i].isDummy())
             continue;
-        JSAtom* atom = AtomStateOffsetToName(*rt->commonNames, table[i].atomOffset);
+        JSAtom* atom = AtomStateOffsetToName(names, table[i].atomOffset);
         MOZ_ASSERT(atom);
         if (name == atom)
             return &table[i];
@@ -1220,11 +1219,10 @@ JS_ResolveStandardClass(JSContext* cx, HandleObject obj, HandleId id, bool* reso
     if (!rt->hasContexts() || !JSID_IS_ATOM(id))
         return true;
 
-    RootedString idstr(cx, JSID_TO_STRING(id));
-
     /* Check whether we're resolving 'undefined', and define it if so. */
+    JSAtom* idAtom = JSID_TO_ATOM(id);
     JSAtom* undefinedAtom = cx->names().undefined;
-    if (idstr == undefinedAtom) {
+    if (idAtom == undefinedAtom) {
         *resolved = true;
         return DefineProperty(cx, obj, undefinedAtom->asPropertyName(),
                               UndefinedHandleValue, nullptr, nullptr,
@@ -1232,11 +1230,11 @@ JS_ResolveStandardClass(JSContext* cx, HandleObject obj, HandleId id, bool* reso
     }
 
     /* Try for class constructors/prototypes named by well-known atoms. */
-    stdnm = LookupStdName(rt, idstr, standard_class_names);
+    stdnm = LookupStdName(cx->names(), idAtom, standard_class_names);
 
     /* Try less frequently used top-level functions and constants. */
     if (!stdnm)
-        stdnm = LookupStdName(rt, idstr, builtin_property_names);
+        stdnm = LookupStdName(cx->names(), idAtom, builtin_property_names);
 
     // If this class is anonymous, then it doesn't exist as a global
     // property, so we won't resolve anything.
@@ -1260,6 +1258,27 @@ JS_ResolveStandardClass(JSContext* cx, HandleObject obj, HandleId id, bool* reso
     return true;
 }
 
+JS_PUBLIC_API(bool)
+JS_MayResolveStandardClass(const JSAtomState& names, jsid id, JSObject* maybeObj)
+{
+    MOZ_ASSERT_IF(maybeObj, maybeObj->is<GlobalObject>());
+
+    // The global object's resolve hook is special: JS_ResolveStandardClass
+    // initializes the prototype chain lazily. Only attempt to optimize here
+    // if we know the prototype chain has been initialized.
+    if (!maybeObj || !maybeObj->getProto())
+        return true;
+
+    if (!JSID_IS_ATOM(id))
+        return false;
+
+    JSAtom* atom = JSID_TO_ATOM(id);
+
+    return atom == names.undefined ||
+           LookupStdName(names, atom, standard_class_names) ||
+           LookupStdName(names, atom, builtin_property_names);
+}
+
 JS_PUBLIC_API(bool)
 JS_EnumerateStandardClasses(JSContext* cx, HandleObject obj)
 {
@@ -1305,8 +1324,9 @@ JS_IdToProtoKey(JSContext* cx, HandleId id)
 
     if (!JSID_IS_ATOM(id))
         return JSProto_Null;
-    RootedString idstr(cx, JSID_TO_STRING(id));
-    const JSStdName* stdnm = LookupStdName(cx->runtime(), idstr, standard_class_names);
+
+    JSAtom* atom = JSID_TO_ATOM(id);
+    const JSStdName* stdnm = LookupStdName(cx->names(), atom, standard_class_names);
     if (!stdnm)
         return JSProto_Null;
 
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index 3918b0d837c5..61d6654b50ae 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -1506,6 +1506,9 @@ JS_InitStandardClasses(JSContext* cx, JS::Handle<JSObject*> obj);
 extern JS_PUBLIC_API(bool)
 JS_ResolveStandardClass(JSContext* cx, JS::HandleObject obj, JS::HandleId id, bool* resolved);
 
+extern JS_PUBLIC_API(bool)
+JS_MayResolveStandardClass(const JSAtomState& names, jsid id, JSObject* maybeObj);
+
 extern JS_PUBLIC_API(bool)
 JS_EnumerateStandardClasses(JSContext* cx, JS::HandleObject obj);
 
diff --git a/js/src/jsarray.cpp b/js/src/jsarray.cpp
index 772052733155..66a502b8f353 100644
--- a/js/src/jsarray.cpp
+++ b/js/src/jsarray.cpp
@@ -3249,6 +3249,7 @@ const Class ArrayObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     nullptr, /* finalize */
     nullptr, /* call */
diff --git a/js/src/jsdate.cpp b/js/src/jsdate.cpp
index 58f3fa391882..1b7f78678b50 100644
--- a/js/src/jsdate.cpp
+++ b/js/src/jsdate.cpp
@@ -3044,6 +3044,7 @@ const Class DateObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     date_convert,
     nullptr, /* finalize */
     nullptr, /* call */
diff --git a/js/src/jsexn.cpp b/js/src/jsexn.cpp
index 703ff7de5f34..a5511588f984 100644
--- a/js/src/jsexn.cpp
+++ b/js/src/jsexn.cpp
@@ -77,6 +77,7 @@ static const JSFunctionSpec exception_methods[] = {
         nullptr,                 /* setProperty */ \
         nullptr,                 /* enumerate */ \
         nullptr,                 /* resolve */ \
+        nullptr,                 /* mayResolve */ \
         nullptr,                 /* convert */ \
         exn_finalize, \
         nullptr,                 /* call        */ \
@@ -108,6 +109,7 @@ ErrorObject::classes[JSEXN_LIMIT] = {
         nullptr,                 /* setProperty */
         nullptr,                 /* enumerate */
         nullptr,                 /* resolve */
+        nullptr,                 /* mayResolve */
         nullptr,                 /* convert */
         exn_finalize,
         nullptr,                 /* call        */
diff --git a/js/src/jsfriendapi.h b/js/src/jsfriendapi.h
index 7dd7aa217f3b..ade724c5928b 100644
--- a/js/src/jsfriendapi.h
+++ b/js/src/jsfriendapi.h
@@ -319,6 +319,7 @@ namespace js {
         nullptr,                 /* setProperty */                                      \
         nullptr,                 /* enumerate */                                        \
         nullptr,                 /* resolve */                                          \
+        nullptr,                 /* mayResolve */                                       \
         js::proxy_Convert,                                                              \
         js::proxy_Finalize,      /* finalize    */                                      \
         nullptr,                 /* call        */                                      \
diff --git a/js/src/jsfun.cpp b/js/src/jsfun.cpp
index 6da5747f8b53..9d9862e58fb4 100644
--- a/js/src/jsfun.cpp
+++ b/js/src/jsfun.cpp
@@ -419,18 +419,18 @@ ResolveInterpretedFunctionPrototype(JSContext* cx, HandleObject obj)
     return proto;
 }
 
-bool
-js::FunctionHasResolveHook(const JSAtomState& atomState, jsid id)
+static bool
+fun_mayResolve(const JSAtomState& names, jsid id, JSObject*)
 {
     if (!JSID_IS_ATOM(id))
         return false;
 
     JSAtom* atom = JSID_TO_ATOM(id);
-    return atom == atomState.prototype || atom == atomState.length || atom == atomState.name;
+    return atom == names.prototype || atom == names.length || atom == names.name;
 }
 
-bool
-js::fun_resolve(JSContext* cx, HandleObject obj, HandleId id, bool* resolvedp)
+static bool
+fun_resolve(JSContext* cx, HandleObject obj, HandleId id, bool* resolvedp)
 {
     if (!JSID_IS_ATOM(id))
         return true;
@@ -891,7 +891,8 @@ const Class JSFunction::class_ = {
     nullptr,                 /* getProperty */
     nullptr,                 /* setProperty */
     fun_enumerate,
-    js::fun_resolve,
+    fun_resolve,
+    fun_mayResolve,
     nullptr,                 /* convert     */
     nullptr,                 /* finalize    */
     nullptr,                 /* call        */
diff --git a/js/src/jsfun.h b/js/src/jsfun.h
index cf4a5e999281..ba008df11cd8 100644
--- a/js/src/jsfun.h
+++ b/js/src/jsfun.h
@@ -53,8 +53,8 @@ class JSFunction : public js::NativeObject
                                        must be constructible but not decompilable. */
         HAS_REST         = 0x0200,  /* function has a rest (...) parameter */
         INTERPRETED_LAZY = 0x0400,  /* function is interpreted but doesn't have a script yet */
-        RESOLVED_LENGTH  = 0x0800,  /* f.length has been resolved (see js::fun_resolve). */
-        RESOLVED_NAME    = 0x1000,  /* f.name has been resolved (see js::fun_resolve). */
+        RESOLVED_LENGTH  = 0x0800,  /* f.length has been resolved (see fun_resolve). */
+        RESOLVED_NAME    = 0x1000,  /* f.name has been resolved (see fun_resolve). */
 
         FUNCTION_KIND_SHIFT = 13,
         FUNCTION_KIND_MASK  = 0x3 << FUNCTION_KIND_SHIFT,
@@ -568,9 +568,6 @@ DefineFunction(JSContext* cx, HandleObject obj, HandleId id, JSNative native,
 bool
 FunctionHasResolveHook(const JSAtomState& atomState, jsid id);
 
-extern bool
-fun_resolve(JSContext* cx, HandleObject obj, HandleId id, bool* resolvedp);
-
 extern bool
 fun_toString(JSContext* cx, unsigned argc, Value* vp);
 
diff --git a/js/src/jsiter.cpp b/js/src/jsiter.cpp
index eb02601a7b3f..041958b7f08b 100644
--- a/js/src/jsiter.cpp
+++ b/js/src/jsiter.cpp
@@ -988,6 +988,7 @@ const Class PropertyIteratorObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     finalize,
     nullptr, /* call        */
@@ -1375,6 +1376,7 @@ const Class StopIterationObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     nullptr, /* finalize */
     nullptr, /* call */
diff --git a/js/src/jsobj.cpp b/js/src/jsobj.cpp
index 7c7fde519fbb..39fa4770c4d6 100644
--- a/js/src/jsobj.cpp
+++ b/js/src/jsobj.cpp
@@ -2784,19 +2784,10 @@ js::LookupPropertyPure(ExclusiveContext* cx, JSObject* obj, jsid id, JSObject**
                 return true;
             }
 
-            // Fail if there's a resolve hook. We allow the JSFunction resolve hook
-            // if we know it will never add a property with this name or str_resolve
-            // with a non-integer property.
-            do {
-                const Class* clasp = obj->getClass();
-                if (!clasp->resolve)
-                    break;
-                if (clasp->resolve == fun_resolve && !FunctionHasResolveHook(cx->names(), id))
-                    break;
-                if (clasp->resolve == str_resolve && !JSID_IS_INT(id))
-                    break;
+            // Fail if there's a resolve hook, unless the mayResolve hook tells
+            // us the resolve hook won't define a property with this id.
+            if (ClassMayResolveId(cx->names(), obj->getClass(), id, obj))
                 return false;
-            } while (0);
         } else if (obj->is<UnboxedPlainObject>()) {
             if (obj->as<UnboxedPlainObject>().containsUnboxedOrExpandoProperty(cx, id)) {
                 *objp = obj;
diff --git a/js/src/jsscript.cpp b/js/src/jsscript.cpp
index 26ef199aebd7..abc7a5e24ff3 100644
--- a/js/src/jsscript.cpp
+++ b/js/src/jsscript.cpp
@@ -1361,6 +1361,7 @@ const Class ScriptSourceObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     finalize,
     nullptr, /* call */
diff --git a/js/src/jsstr.cpp b/js/src/jsstr.cpp
index 7752217af047..2fc3c3924e68 100644
--- a/js/src/jsstr.cpp
+++ b/js/src/jsstr.cpp
@@ -394,8 +394,15 @@ str_enumerate(JSContext* cx, HandleObject obj)
     return true;
 }
 
-bool
-js::str_resolve(JSContext* cx, HandleObject obj, HandleId id, bool* resolvedp)
+static bool
+str_mayResolve(const JSAtomState&, jsid id, JSObject*)
+{
+    // str_resolve ignores non-integer ids.
+    return JSID_IS_INT(id);
+}
+
+static bool
+str_resolve(JSContext* cx, HandleObject obj, HandleId id, bool* resolvedp)
 {
     if (!JSID_IS_INT(id))
         return true;
@@ -424,7 +431,8 @@ const Class StringObject::class_ = {
     nullptr, /* getProperty */
     nullptr, /* setProperty */
     str_enumerate,
-    str_resolve
+    str_resolve,
+    str_mayResolve
 };
 
 /*
diff --git a/js/src/jsstr.h b/js/src/jsstr.h
index 217a85077fdc..feec7846e1e4 100644
--- a/js/src/jsstr.h
+++ b/js/src/jsstr.h
@@ -408,9 +408,6 @@ str_split(JSContext* cx, unsigned argc, Value* vp);
 JSObject*
 str_split_string(JSContext* cx, HandleObjectGroup group, HandleString str, HandleString sep);
 
-bool
-str_resolve(JSContext* cx, HandleObject obj, HandleId id, bool* resolvedp);
-
 bool
 str_replace_regexp_raw(JSContext* cx, HandleString string, HandleObject regexp,
                        HandleString replacement, MutableHandleValue rval);
diff --git a/js/src/jsweakmap.cpp b/js/src/jsweakmap.cpp
index 97a660e9ce39..027076214949 100644
--- a/js/src/jsweakmap.cpp
+++ b/js/src/jsweakmap.cpp
@@ -616,6 +616,7 @@ const Class WeakMapObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     WeakMap_finalize,
     nullptr, /* call */
diff --git a/js/src/perf/jsperf.cpp b/js/src/perf/jsperf.cpp
index d113db0cce3f..143ea2a468e2 100644
--- a/js/src/perf/jsperf.cpp
+++ b/js/src/perf/jsperf.cpp
@@ -163,7 +163,7 @@ static void pm_finalize(JSFreeOp* fop, JSObject* obj);
 
 static const JSClass pm_class = {
     "PerfMeasurement", JSCLASS_HAS_PRIVATE,
-    nullptr, nullptr, nullptr, nullptr,
+    nullptr, nullptr, nullptr, nullptr, nullptr,
     nullptr, nullptr, nullptr, pm_finalize
 };
 
diff --git a/js/src/shell/js.cpp b/js/src/shell/js.cpp
index 0bf8e8c92ce0..4f0e1b4ada69 100644
--- a/js/src/shell/js.cpp
+++ b/js/src/shell/js.cpp
@@ -2660,7 +2660,7 @@ static const JSClass sandbox_class = {
     JSCLASS_GLOBAL_FLAGS,
     nullptr, nullptr, nullptr, nullptr,
     sandbox_enumerate, sandbox_resolve,
-    nullptr, nullptr,
+    nullptr, nullptr, nullptr,
     nullptr, nullptr, nullptr,
     JS_GlobalObjectTraceHook
 };
@@ -5119,10 +5119,16 @@ global_resolve(JSContext* cx, HandleObject obj, HandleId id, bool* resolvedp)
     return true;
 }
 
+static bool
+global_mayResolve(const JSAtomState& names, jsid id, JSObject* maybeObj)
+{
+    return JS_MayResolveStandardClass(names, id, maybeObj);
+}
+
 static const JSClass global_class = {
     "global", JSCLASS_GLOBAL_FLAGS,
     nullptr, nullptr, nullptr, nullptr,
-    global_enumerate, global_resolve,
+    global_enumerate, global_resolve, global_mayResolve,
     nullptr, nullptr,
     nullptr, nullptr, nullptr,
     JS_GlobalObjectTraceHook
diff --git a/js/src/vm/ArgumentsObject.cpp b/js/src/vm/ArgumentsObject.cpp
index 1352b1f9b0e4..73539d58cb74 100644
--- a/js/src/vm/ArgumentsObject.cpp
+++ b/js/src/vm/ArgumentsObject.cpp
@@ -560,6 +560,7 @@ const Class NormalArgumentsObject::class_ = {
     nullptr,                 /* setProperty */
     args_enumerate,
     args_resolve,
+    nullptr,                 /* mayResolve  */
     nullptr,                 /* convert     */
     ArgumentsObject::finalize,
     nullptr,                 /* call        */
@@ -584,6 +585,7 @@ const Class StrictArgumentsObject::class_ = {
     nullptr,                 /* setProperty */
     strictargs_enumerate,
     strictargs_resolve,
+    nullptr,                 /* mayResolve  */
     nullptr,                 /* convert     */
     ArgumentsObject::finalize,
     nullptr,                 /* call        */
diff --git a/js/src/vm/ArrayBufferObject.cpp b/js/src/vm/ArrayBufferObject.cpp
index 39a03adcd762..c73f0b7be6ab 100644
--- a/js/src/vm/ArrayBufferObject.cpp
+++ b/js/src/vm/ArrayBufferObject.cpp
@@ -108,6 +108,7 @@ const Class ArrayBufferObject::class_ = {
     nullptr,                 /* setProperty */
     nullptr,                 /* enumerate */
     nullptr,                 /* resolve */
+    nullptr,                 /* mayResolve */
     nullptr,                 /* convert */
     ArrayBufferObject::finalize,
     nullptr,        /* call        */
diff --git a/js/src/vm/Debugger.cpp b/js/src/vm/Debugger.cpp
index 566c48cb4f73..ec8db41fcbfb 100644
--- a/js/src/vm/Debugger.cpp
+++ b/js/src/vm/Debugger.cpp
@@ -2405,7 +2405,7 @@ const Class Debugger::jsclass = {
     "Debugger",
     JSCLASS_HAS_PRIVATE | JSCLASS_IMPLEMENTS_BARRIERS |
     JSCLASS_HAS_RESERVED_SLOTS(JSSLOT_DEBUG_COUNT),
-    nullptr, nullptr, nullptr, nullptr,
+    nullptr, nullptr, nullptr, nullptr, nullptr,
     nullptr, nullptr, nullptr, Debugger::finalize,
     nullptr,              /* call        */
     nullptr,              /* hasInstance */
@@ -4204,7 +4204,7 @@ const Class DebuggerScript_class = {
     "Script",
     JSCLASS_HAS_PRIVATE | JSCLASS_IMPLEMENTS_BARRIERS |
     JSCLASS_HAS_RESERVED_SLOTS(JSSLOT_DEBUGSCRIPT_COUNT),
-    nullptr, nullptr, nullptr, nullptr,
+    nullptr, nullptr, nullptr, nullptr, nullptr,
     nullptr, nullptr, nullptr, nullptr,
     nullptr,              /* call        */
     nullptr,              /* hasInstance */
@@ -5225,7 +5225,7 @@ const Class DebuggerSource_class = {
     "Source",
     JSCLASS_HAS_PRIVATE | JSCLASS_IMPLEMENTS_BARRIERS |
     JSCLASS_HAS_RESERVED_SLOTS(JSSLOT_DEBUGSOURCE_COUNT),
-    nullptr, nullptr, nullptr, nullptr,
+    nullptr, nullptr, nullptr, nullptr, nullptr,
     nullptr, nullptr, nullptr, nullptr,
     nullptr,              /* call        */
     nullptr,              /* hasInstance */
@@ -5580,7 +5580,7 @@ DebuggerFrame_finalize(FreeOp* fop, JSObject* obj)
 
 const Class DebuggerFrame_class = {
     "Frame", JSCLASS_HAS_PRIVATE | JSCLASS_HAS_RESERVED_SLOTS(JSSLOT_DEBUGFRAME_COUNT),
-    nullptr, nullptr, nullptr, nullptr,
+    nullptr, nullptr, nullptr, nullptr, nullptr,
     nullptr, nullptr, nullptr, DebuggerFrame_finalize
 };
 
@@ -6342,7 +6342,7 @@ const Class DebuggerObject_class = {
     "Object",
     JSCLASS_HAS_PRIVATE | JSCLASS_IMPLEMENTS_BARRIERS |
     JSCLASS_HAS_RESERVED_SLOTS(JSSLOT_DEBUGOBJECT_COUNT),
-    nullptr, nullptr, nullptr, nullptr,
+    nullptr, nullptr, nullptr, nullptr, nullptr,
     nullptr, nullptr, nullptr, nullptr,
     nullptr,              /* call        */
     nullptr,              /* hasInstance */
@@ -7252,7 +7252,7 @@ const Class DebuggerEnv_class = {
     "Environment",
     JSCLASS_HAS_PRIVATE | JSCLASS_IMPLEMENTS_BARRIERS |
     JSCLASS_HAS_RESERVED_SLOTS(JSSLOT_DEBUGENV_COUNT),
-    nullptr, nullptr, nullptr, nullptr,
+    nullptr, nullptr, nullptr, nullptr, nullptr,
     nullptr, nullptr, nullptr, nullptr,
     nullptr,              /* call        */
     nullptr,              /* hasInstance */
diff --git a/js/src/vm/GlobalObject.cpp b/js/src/vm/GlobalObject.cpp
index 39c20a3ce7d3..badefdfffa0b 100644
--- a/js/src/vm/GlobalObject.cpp
+++ b/js/src/vm/GlobalObject.cpp
@@ -506,7 +506,7 @@ GlobalDebuggees_finalize(FreeOp* fop, JSObject* obj)
 static const Class
 GlobalDebuggees_class = {
     "GlobalDebuggee", JSCLASS_HAS_PRIVATE,
-    nullptr, nullptr, nullptr, nullptr,
+    nullptr, nullptr, nullptr, nullptr, nullptr,
     nullptr, nullptr, nullptr, GlobalDebuggees_finalize
 };
 
diff --git a/js/src/vm/HelperThreads.cpp b/js/src/vm/HelperThreads.cpp
index bcd75cc8234d..536fd45b668a 100644
--- a/js/src/vm/HelperThreads.cpp
+++ b/js/src/vm/HelperThreads.cpp
@@ -192,7 +192,7 @@ static const JSClass parseTaskGlobalClass = {
     "internal-parse-task-global", JSCLASS_GLOBAL_FLAGS,
     nullptr, nullptr, nullptr, nullptr,
     nullptr, nullptr, nullptr, nullptr,
-    nullptr, nullptr, nullptr,
+    nullptr, nullptr, nullptr, nullptr,
     JS_GlobalObjectTraceHook
 };
 
diff --git a/js/src/vm/NativeObject-inl.h b/js/src/vm/NativeObject-inl.h
index 98e5c6adddeb..b13bdf1facb9 100644
--- a/js/src/vm/NativeObject-inl.h
+++ b/js/src/vm/NativeObject-inl.h
@@ -414,6 +414,11 @@ CallResolveOp(JSContext* cx, HandleNativeObject obj, HandleId id, MutableHandleS
     if (!resolved)
         return true;
 
+    // Assert the mayResolve hook, if there is one, returns true for this
+    // property.
+    MOZ_ASSERT_IF(obj->getClass()->mayResolve,
+                  obj->getClass()->mayResolve(cx->names(), id, obj));
+
     if (JSID_IS_INT(id) && obj->containsDenseElement(JSID_TO_INT(id))) {
         MarkDenseOrTypedArrayElementFound<CanGC>(propp);
         return true;
@@ -425,6 +430,28 @@ CallResolveOp(JSContext* cx, HandleNativeObject obj, HandleId id, MutableHandleS
     return true;
 }
 
+static MOZ_ALWAYS_INLINE bool
+ClassMayResolveId(const JSAtomState& names, const Class* clasp, jsid id, JSObject* maybeObj)
+{
+    MOZ_ASSERT_IF(maybeObj, maybeObj->getClass() == clasp);
+
+    if (!clasp->resolve) {
+        // Sanity check: we should only have a mayResolve hook if we have a
+        // resolve hook.
+        MOZ_ASSERT(!clasp->mayResolve, "Class with mayResolve hook but no resolve hook");
+        return false;
+    }
+
+    if (clasp->mayResolve) {
+        // Tell the analysis our mayResolve hooks won't trigger GC.
+        JS::AutoSuppressGCAnalysis nogc;
+        if (!clasp->mayResolve(names, id, maybeObj))
+            return false;
+    }
+
+    return true;
+}
+
 template <AllowGC allowGC>
 static MOZ_ALWAYS_INLINE bool
 LookupOwnPropertyInline(ExclusiveContext* cx,
diff --git a/js/src/vm/PIC.cpp b/js/src/vm/PIC.cpp
index 36bb59189a7f..4019d11cbd4d 100644
--- a/js/src/vm/PIC.cpp
+++ b/js/src/vm/PIC.cpp
@@ -296,7 +296,7 @@ ForOfPIC_traceObject(JSTracer* trc, JSObject* obj)
 
 const Class ForOfPIC::jsclass = {
     "ForOfPIC", JSCLASS_HAS_PRIVATE | JSCLASS_IMPLEMENTS_BARRIERS,
-    nullptr, nullptr, nullptr, nullptr,
+    nullptr, nullptr, nullptr, nullptr, nullptr,
     nullptr, nullptr, nullptr, ForOfPIC_finalize,
     nullptr,              /* call        */
     nullptr,              /* hasInstance */
diff --git a/js/src/vm/RegExpObject.cpp b/js/src/vm/RegExpObject.cpp
index dd9dbc1a90a4..e50ff21c6ecb 100644
--- a/js/src/vm/RegExpObject.cpp
+++ b/js/src/vm/RegExpObject.cpp
@@ -269,6 +269,7 @@ const Class RegExpObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     nullptr, /* finalize */
     nullptr, /* call */
diff --git a/js/src/vm/RegExpStatics.cpp b/js/src/vm/RegExpStatics.cpp
index 2732f8b30840..5e72091a8f1b 100644
--- a/js/src/vm/RegExpStatics.cpp
+++ b/js/src/vm/RegExpStatics.cpp
@@ -44,6 +44,7 @@ const Class RegExpStaticsObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     resc_finalize,
     nullptr, /* call */
diff --git a/js/src/vm/SavedStacks.cpp b/js/src/vm/SavedStacks.cpp
index da1819c8111e..0ca9b14efbea 100644
--- a/js/src/vm/SavedStacks.cpp
+++ b/js/src/vm/SavedStacks.cpp
@@ -185,6 +185,7 @@ SavedFrame::finishSavedFrameInit(JSContext* cx, HandleObject ctor, HandleObject
     nullptr,                    // setProperty
     nullptr,                    // enumerate
     nullptr,                    // resolve
+    nullptr,                    // mayResolve
     nullptr,                    // convert
     SavedFrame::finalize,       // finalize
     nullptr,                    // call
diff --git a/js/src/vm/ScopeObject.cpp b/js/src/vm/ScopeObject.cpp
index e5eed90776d3..dbc432944de2 100644
--- a/js/src/vm/ScopeObject.cpp
+++ b/js/src/vm/ScopeObject.cpp
@@ -540,6 +540,7 @@ const Class DynamicWithObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     nullptr, /* finalize */
     nullptr, /* call */
@@ -977,6 +978,7 @@ const Class UninitializedLexicalObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     nullptr, /* finalize */
     nullptr, /* call */
diff --git a/js/src/vm/SelfHosting.cpp b/js/src/vm/SelfHosting.cpp
index 7358a6670b9d..199ae9466528 100644
--- a/js/src/vm/SelfHosting.cpp
+++ b/js/src/vm/SelfHosting.cpp
@@ -1542,7 +1542,7 @@ JSRuntime::createSelfHostingGlobal(JSContext* cx)
         "self-hosting-global", JSCLASS_GLOBAL_FLAGS,
         nullptr, nullptr, nullptr, nullptr,
         nullptr, nullptr, nullptr, nullptr,
-        nullptr, nullptr, nullptr,
+        nullptr, nullptr, nullptr, nullptr,
         JS_GlobalObjectTraceHook
     };
 
diff --git a/js/src/vm/SharedArrayObject.cpp b/js/src/vm/SharedArrayObject.cpp
index 1d666cad1574..32234681d1c7 100644
--- a/js/src/vm/SharedArrayObject.cpp
+++ b/js/src/vm/SharedArrayObject.cpp
@@ -313,6 +313,7 @@ const Class SharedArrayBufferObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     SharedArrayBufferObject::Finalize,
     nullptr, /* call */
diff --git a/js/src/vm/SharedTypedArrayObject.cpp b/js/src/vm/SharedTypedArrayObject.cpp
index 37b4132595d4..16b582962dd2 100644
--- a/js/src/vm/SharedTypedArrayObject.cpp
+++ b/js/src/vm/SharedTypedArrayObject.cpp
@@ -711,6 +711,7 @@ IMPL_SHARED_TYPED_ARRAY_COMBINED_UNWRAPPERS(Float64, double, double)
     nullptr,                 /* setProperty */                                 \
     nullptr,                 /* enumerate   */                                 \
     nullptr,                 /* resolve     */                                 \
+    nullptr,                 /* mayResolve  */                                 \
     nullptr,                 /* convert     */                                 \
     nullptr,                 /* finalize    */                                 \
     nullptr,                 /* call        */                                 \
@@ -732,6 +733,7 @@ IMPL_SHARED_TYPED_ARRAY_COMBINED_UNWRAPPERS(Float64, double, double)
     nullptr,                 /* setProperty */                                 \
     nullptr,                 /* enumerate   */                                 \
     nullptr,                 /* resolve     */                                 \
+    nullptr,                 /* mayResolve  */                                 \
     nullptr,                 /* convert     */                                 \
     nullptr,                 /* finalize    */                                 \
     nullptr,                 /* call        */                                 \
diff --git a/js/src/vm/TypedArrayObject.cpp b/js/src/vm/TypedArrayObject.cpp
index d710804ac71c..568779fb165e 100644
--- a/js/src/vm/TypedArrayObject.cpp
+++ b/js/src/vm/TypedArrayObject.cpp
@@ -839,6 +839,7 @@ TypedArrayObject::sharedTypedArrayPrototypeClass = {
     nullptr,                /* setProperty */
     nullptr,                /* enumerate */
     nullptr,                /* resolve */
+    nullptr,                /* mayResolve */
     nullptr,                /* convert */
     nullptr,                /* finalize */
     nullptr,                /* call */
@@ -1801,6 +1802,7 @@ IMPL_TYPED_ARRAY_COMBINED_UNWRAPPERS(Float64, double, double)
     nullptr,                 /* setProperty */                                 \
     nullptr,                 /* enumerate   */                                 \
     nullptr,                 /* resolve     */                                 \
+    nullptr,                 /* mayResolve  */                                 \
     nullptr,                 /* convert     */                                 \
     nullptr,                 /* finalize    */                                 \
     nullptr,                 /* call        */                                 \
@@ -1846,6 +1848,7 @@ const Class TypedArrayObject::classes[Scalar::MaxTypedArrayViewType] = {
     nullptr, /* setProperty */ \
     nullptr, /* enumerate */ \
     nullptr, /* resolve */ \
+    nullptr, /* mayResolve */ \
     nullptr, /* convert */ \
     nullptr, /* finalize */ \
     nullptr, /* call */ \
@@ -1901,6 +1904,7 @@ const Class DataViewObject::class_ = {
     nullptr, /* setProperty */
     nullptr, /* enumerate */
     nullptr, /* resolve */
+    nullptr, /* mayResolve */
     nullptr, /* convert */
     nullptr, /* finalize */
     nullptr, /* call */
diff --git a/js/src/vm/UnboxedObject.cpp b/js/src/vm/UnboxedObject.cpp
index 763896e7f26c..2d2865cf9cf9 100644
--- a/js/src/vm/UnboxedObject.cpp
+++ b/js/src/vm/UnboxedObject.cpp
@@ -893,6 +893,7 @@ const Class UnboxedPlainObject::class_ = {
     nullptr,        /* setProperty */
     nullptr,        /* enumerate   */
     nullptr,        /* resolve     */
+    nullptr,        /* mayResolve  */
     nullptr,        /* convert     */
     nullptr,        /* finalize    */
     nullptr,        /* call        */
diff --git a/js/xpconnect/src/Sandbox.cpp b/js/xpconnect/src/Sandbox.cpp
index 99f3ec4e7705..b2ca02d92b51 100644
--- a/js/xpconnect/src/Sandbox.cpp
+++ b/js/xpconnect/src/Sandbox.cpp
@@ -468,7 +468,9 @@ static const js::Class SandboxClass = {
     "Sandbox",
     XPCONNECT_GLOBAL_FLAGS_WITH_EXTRA_SLOTS(1),
     nullptr, nullptr, nullptr, nullptr,
-    sandbox_enumerate, sandbox_resolve, sandbox_convert,  sandbox_finalize,
+    sandbox_enumerate, sandbox_resolve,
+    nullptr,        /* mayResolve */
+    sandbox_convert,  sandbox_finalize,
     nullptr, nullptr, nullptr, JS_GlobalObjectTraceHook,
     JS_NULL_CLASS_SPEC,
     {
@@ -487,7 +489,9 @@ static const js::Class SandboxWriteToProtoClass = {
     "Sandbox",
     XPCONNECT_GLOBAL_FLAGS_WITH_EXTRA_SLOTS(1),
     sandbox_addProperty, nullptr, nullptr, nullptr,
-    sandbox_enumerate, sandbox_resolve, sandbox_convert,  sandbox_finalize,
+    sandbox_enumerate, sandbox_resolve,
+    nullptr,        /* mayResolve */
+    sandbox_convert,  sandbox_finalize,
     nullptr, nullptr, nullptr, JS_GlobalObjectTraceHook,
     JS_NULL_CLASS_SPEC,
     {
diff --git a/js/xpconnect/src/XPCWrappedJSClass.cpp b/js/xpconnect/src/XPCWrappedJSClass.cpp
index ab7f2b90f2bc..3c67954a10b6 100644
--- a/js/xpconnect/src/XPCWrappedJSClass.cpp
+++ b/js/xpconnect/src/XPCWrappedJSClass.cpp
@@ -1456,6 +1456,7 @@ static const JSClass XPCOutParamClass = {
     nullptr,   /* setProperty */
     nullptr,   /* enumerate */
     nullptr,   /* resolve */
+    nullptr,   /* mayResolve */
     nullptr,   /* convert */
     FinalizeStub,
     nullptr,   /* call */
diff --git a/js/xpconnect/src/XPCWrappedNativeJSOps.cpp b/js/xpconnect/src/XPCWrappedNativeJSOps.cpp
index e42501dde5a6..ae1e1b565d9d 100644
--- a/js/xpconnect/src/XPCWrappedNativeJSOps.cpp
+++ b/js/xpconnect/src/XPCWrappedNativeJSOps.cpp
@@ -648,6 +648,7 @@ const XPCWrappedNativeJSClass XPC_WN_NoHelper_JSClass = {
 
     XPC_WN_Shared_Enumerate,           // enumerate
     XPC_WN_NoHelper_Resolve,           // resolve
+    nullptr,                           // mayResolve
     XPC_WN_Shared_Convert,             // convert
     XPC_WN_NoHelper_Finalize,          // finalize
 
@@ -1288,6 +1289,7 @@ const js::Class XPC_WN_ModsAllowed_WithCall_Proto_JSClass = {
     nullptr,                        // setProperty;
     XPC_WN_Shared_Proto_Enumerate,  // enumerate;
     XPC_WN_ModsAllowed_Proto_Resolve, // resolve;
+    nullptr,                        // mayResolve;
     nullptr,                        // convert;
     XPC_WN_Shared_Proto_Finalize,   // finalize;
 
@@ -1313,6 +1315,7 @@ const js::Class XPC_WN_ModsAllowed_NoCall_Proto_JSClass = {
     nullptr,                        // setProperty;
     XPC_WN_Shared_Proto_Enumerate,  // enumerate;
     XPC_WN_ModsAllowed_Proto_Resolve, // resolve;
+    nullptr,                        // mayResolve;
     nullptr,                        // convert;
     XPC_WN_Shared_Proto_Finalize,   // finalize;
 
@@ -1391,6 +1394,7 @@ const js::Class XPC_WN_NoMods_WithCall_Proto_JSClass = {
     nullptr,                                   // setProperty;
     XPC_WN_Shared_Proto_Enumerate,             // enumerate;
     XPC_WN_NoMods_Proto_Resolve,               // resolve;
+    nullptr,                                   // mayResolve;
     nullptr,                                   // convert;
     XPC_WN_Shared_Proto_Finalize,              // finalize;
 
@@ -1416,6 +1420,7 @@ const js::Class XPC_WN_NoMods_NoCall_Proto_JSClass = {
     nullptr,                                   // setProperty;
     XPC_WN_Shared_Proto_Enumerate,             // enumerate;
     XPC_WN_NoMods_Proto_Resolve,               // resolve;
+    nullptr,                                   // mayResolve;
     nullptr,                                   // convert;
     XPC_WN_Shared_Proto_Finalize,              // finalize;
 
@@ -1511,6 +1516,7 @@ const js::Class XPC_WN_Tearoff_JSClass = {
     nullptr,                                   // setProperty;
     XPC_WN_TearOff_Enumerate,                  // enumerate;
     XPC_WN_TearOff_Resolve,                    // resolve;
+    nullptr,                                   // mayResolve;
     XPC_WN_Shared_Convert,                     // convert;
     XPC_WN_TearOff_Finalize,                   // finalize;
 
diff --git a/js/xpconnect/wrappers/XrayWrapper.cpp b/js/xpconnect/wrappers/XrayWrapper.cpp
index 21ce6ff77b11..55c024a02f48 100644
--- a/js/xpconnect/wrappers/XrayWrapper.cpp
+++ b/js/xpconnect/wrappers/XrayWrapper.cpp
@@ -887,7 +887,7 @@ ExpandoObjectFinalize(JSFreeOp* fop, JSObject* obj)
 const JSClass ExpandoObjectClass = {
     "XrayExpandoObject",
     JSCLASS_HAS_RESERVED_SLOTS(JSSLOT_EXPANDO_COUNT),
-    nullptr, nullptr, nullptr, nullptr,
+    nullptr, nullptr, nullptr, nullptr, nullptr,
     nullptr, nullptr, nullptr, ExpandoObjectFinalize
 };
 
diff --git a/netwerk/base/ProxyAutoConfig.cpp b/netwerk/base/ProxyAutoConfig.cpp
index 994608c99b8b..a7dddb9191dc 100644
--- a/netwerk/base/ProxyAutoConfig.cpp
+++ b/netwerk/base/ProxyAutoConfig.cpp
@@ -669,7 +669,7 @@ const JSClass JSRuntimeWrapper::sGlobalClass = {
   "PACResolutionThreadGlobal",
   JSCLASS_GLOBAL_FLAGS,
   nullptr, nullptr, nullptr, nullptr,
-  nullptr, nullptr, nullptr,
+  nullptr, nullptr, nullptr, nullptr,
   nullptr, nullptr, nullptr, nullptr,
   JS_GlobalObjectTraceHook
 };
diff --git a/toolkit/components/finalizationwitness/FinalizationWitnessService.cpp b/toolkit/components/finalizationwitness/FinalizationWitnessService.cpp
index dd70c4c87a48..0678ceddd2f5 100644
--- a/toolkit/components/finalizationwitness/FinalizationWitnessService.cpp
+++ b/toolkit/components/finalizationwitness/FinalizationWitnessService.cpp
@@ -120,6 +120,7 @@ static const JSClass sWitnessClass = {
   nullptr /* setProperty */,
   nullptr /* enumerate */,
   nullptr /* resolve */,
+  nullptr /* mayResolve */,
   nullptr /* convert */,
   Finalize /* finalize */
 };
diff --git a/xpcom/glue/tests/gtest/TestGCPostBarriers.cpp b/xpcom/glue/tests/gtest/TestGCPostBarriers.cpp
index 569b7a6af5e6..c44b8c2e27e0 100644
--- a/xpcom/glue/tests/gtest/TestGCPostBarriers.cpp
+++ b/xpcom/glue/tests/gtest/TestGCPostBarriers.cpp
@@ -88,7 +88,7 @@ CreateGlobalAndRunTest(JSRuntime* rt, JSContext* cx)
     "global", JSCLASS_GLOBAL_FLAGS,
     nullptr, nullptr, nullptr, nullptr,
     nullptr, nullptr, nullptr, nullptr,
-    nullptr, nullptr, nullptr,
+    nullptr, nullptr, nullptr, nullptr,
     JS_GlobalObjectTraceHook
   };