--- a/js/src/gc/Marking.cpp
+++ b/js/src/gc/Marking.cpp
@@ -1503,24 +1503,24 @@ struct UnmarkGrayTracer : public JSTrace
     /*
      * We set eagerlyTraceWeakMaps to false because the cycle collector will fix
      * up any color mismatches involving weakmaps when it runs.
      */
     UnmarkGrayTracer(JSRuntime *rt)
       : tracingShape(false), previousShape(NULL)
     {
         JS_TracerInit(this, rt, UnmarkGrayChildren);
-        eagerlyTraceWeakMaps = false;
+        eagerlyTraceWeakMaps = DoNotTraceWeakMaps;
     }
 
     UnmarkGrayTracer(JSTracer *trc, bool tracingShape)
       : tracingShape(tracingShape), previousShape(NULL)
     {
         JS_TracerInit(this, trc->runtime, UnmarkGrayChildren);
-        eagerlyTraceWeakMaps = false;
+        eagerlyTraceWeakMaps = DoNotTraceWeakMaps;
     }
 
     /* True iff we are tracing the immediate children of a shape. */
     bool tracingShape;
 
     /* If tracingShape, shape child or NULL. Otherwise, NULL. */
     void *previousShape;
 };

--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -2652,23 +2652,28 @@ JSVAL_TRACE_KIND(jsval v)
  *
  * If eagerlyTraceWeakMaps is true, when we trace a WeakMap visit all
  * of its mappings.  This should be used in cases where the tracer
  * wants to use the existing liveness of entries.
  */
 typedef void
 (* JSTraceCallback)(JSTracer *trc, void **thingp, JSGCTraceKind kind);
 
+enum WeakMapTraceKind {
+    DoNotTraceWeakMaps = 0,
+    TraceWeakMapValues = 1
+};
+
 struct JSTracer {
     JSRuntime           *runtime;
     JSTraceCallback     callback;
     JSTraceNamePrinter  debugPrinter;
     const void          *debugPrintArg;
     size_t              debugPrintIndex;
-    JSBool              eagerlyTraceWeakMaps;
+    WeakMapTraceKind    eagerlyTraceWeakMaps;
 #ifdef JS_GC_ZEAL
     void                *realLocation;
 #endif
 };
 
 /*
  * The method to call on each reference to a traceable thing stored in a
  * particular JSObject or other runtime structure. With DEBUG defined the

--- a/js/src/jsgc.cpp
+++ b/js/src/jsgc.cpp
@@ -1619,17 +1619,17 @@ js_UnlockThing(JSRuntime *rt, void *thin
 void
 js::InitTracer(JSTracer *trc, JSRuntime *rt, JSTraceCallback callback)
 {
     trc->runtime = rt;
     trc->callback = callback;
     trc->debugPrinter = NULL;
     trc->debugPrintArg = NULL;
     trc->debugPrintIndex = size_t(-1);
-    trc->eagerlyTraceWeakMaps = true;
+    trc->eagerlyTraceWeakMaps = TraceWeakMapValues;
 #ifdef JS_GC_ZEAL
     trc->realLocation = NULL;
 #endif
 }
 
 /* static */ int64_t
 SliceBudget::TimeBudget(int64_t millis)
 {
@@ -1698,17 +1698,17 @@ GCMarker::start()
 
     JS_ASSERT(!unmarkedArenaStackTop);
     JS_ASSERT(markLaterArenas == 0);
 
     /*
      * The GC is recomputing the liveness of WeakMap entries, so we delay
      * visting entries.
      */
-    eagerlyTraceWeakMaps = JS_FALSE;
+    eagerlyTraceWeakMaps = DoNotTraceWeakMaps;
 }
 
 void
 GCMarker::stop()
 {
     JS_ASSERT(isDrained());
 
     JS_ASSERT(started);

--- a/js/xpconnect/src/nsXPConnect.cpp
+++ b/js/xpconnect/src/nsXPConnect.cpp
@@ -768,17 +768,17 @@ NoteJSChildTracerShim(JSTracer *trc, voi
 
 static inline void
 NoteGCThingJSChildren(JSRuntime *rt, void *p, JSGCTraceKind traceKind,
                       nsCycleCollectionTraversalCallback &cb)
 {
     MOZ_ASSERT(rt);
     TraversalTracer trc(cb);
     JS_TracerInit(&trc, rt, NoteJSChildTracerShim);
-    trc.eagerlyTraceWeakMaps = false;
+    trc.eagerlyTraceWeakMaps = DoNotTraceWeakMaps;
     JS_TraceChildren(&trc, p, traceKind);
 }
 
 static inline void
 NoteGCThingXPCOMChildren(js::Class *clasp, JSObject *obj,
                          nsCycleCollectionTraversalCallback &cb)
 {
     MOZ_ASSERT(clasp);
@@ -2390,17 +2390,17 @@ public:
          * or is a cross-compartment wrapper. In the former case, we don't need to
          * represent these edges in the CC graph because JS objects are not ref counted.
          * In the latter case, the JS engine keeps a map of these wrappers, which we
          * iterate over.
          */
         TraversalTracer trc(cb);
         JSRuntime *rt = nsXPConnect::GetRuntimeInstance()->GetJSRuntime();
         JS_TracerInit(&trc, rt, NoteJSChildTracerShim);
-        trc.eagerlyTraceWeakMaps = false;
+        trc.eagerlyTraceWeakMaps = DoNotTraceWeakMaps;
         js::VisitGrayWrapperTargets(c, NoteJSChildGrayWrapperShim, &trc);
 
         /*
          * To find C++ children of things in the compartment, we scan every JS Object in
          * the compartment. Only JS Objects can have C++ children.
          */
         js::IterateGrayObjects(c, TraverseObjectShim, &cb);