--- a/js/src/jsarray.cpp
+++ b/js/src/jsarray.cpp
@@ -1216,18 +1216,17 @@ array_toString_sub(JSContext *cx, JSObje
         sep = ,
         seplen = 1;
     }
 
     /*
      * Use HashTable entry as the cycle indicator. On first visit, create the
      * entry, and, when leaving, remove the entry.
      */
-    typedef js::HashSet<JSObject *> ObjSet;
-    ObjSet::AddPtr hashp = cx->busyArrays.lookupForAdd(obj);
+    BusyArraysMap::AddPtr hashp = cx->busyArrays.lookupForAdd(obj);
     uint32 genBefore;
     if (!hashp) {
         /* Not in hash table, so not a cycle. */
         if (!cx->busyArrays.add(hashp, obj))
             return false;
         genBefore = cx->busyArrays.generation();
     } else {
         /* Cycle, so return empty string. */

--- a/js/src/jscntxt.cpp
+++ b/js/src/jscntxt.cpp
@@ -741,16 +741,21 @@ js_NewContext(JSRuntime *rt, size_t stac
 
     JS_InitArenaPool(&cx->tempPool, "temp", TEMP_POOL_CHUNK_SIZE, sizeof(jsdouble),
                      &cx->scriptStackQuota);
     JS_InitArenaPool(&cx->regExpPool, "regExp", TEMP_POOL_CHUNK_SIZE, sizeof(int),
                      &cx->scriptStackQuota);
 
     JS_ASSERT(cx->resolveFlags == 0);
 
+    if (!cx->busyArrays.init()) {
+        FreeContext(cx);
+        return NULL;
+    }
+
 #ifdef JS_THREADSAFE
     if (!js_InitContextThread(cx)) {
         FreeContext(cx);
         return NULL;
     }
 #endif
 
     /*
@@ -836,22 +841,16 @@ js_NewContext(JSRuntime *rt, size_t stac
     }
 
     cxCallback = rt->cxCallback;
     if (cxCallback && !cxCallback(cx, JSCONTEXT_NEW)) {
         js_DestroyContext(cx, JSDCM_NEW_FAILED);
         return NULL;
     }
 
-    /* Using ContextAllocPolicy, so init after JSContext is ready. */
-    if (!cx->busyArrays.init()) {
-        FreeContext(cx);
-        return NULL;
-    }
-
     return cx;
 }
 
 #if defined DEBUG && defined XP_UNIX
 # include <stdio.h>
 
 class JSAutoFile {
 public:
@@ -1989,17 +1988,17 @@ DSTOffsetCache::DSTOffsetCache()
 {
     purge();
 }
 
 JSContext::JSContext(JSRuntime *rt)
   : runtime(rt),
     compartment(NULL),
     regs(NULL),
-    busyArrays(thisInInitializer())
+    busyArrays()
 {}
 
 void
 JSContext::resetCompartment()
 {
     JSObject *scopeobj;
     if (hasfp()) {
         scopeobj = &fp()->scopeChain();

--- a/js/src/jscntxt.h
+++ b/js/src/jscntxt.h
@@ -1628,16 +1628,20 @@ VersionHasFlags(JSVersion version)
 }
 
 static inline bool
 VersionIsKnown(JSVersion version)
 {
     return VersionNumber(version) != JSVERSION_UNKNOWN;
 }
 
+typedef js::HashSet<JSObject *,
+                    js::DefaultHasher<JSObject *>,
+                    js::SystemAllocPolicy> BusyArraysMap;
+
 } /* namespace js */
 
 struct JSContext
 {
     explicit JSContext(JSRuntime *rt);
 
     /* JSRuntime contextList linkage. */
     JSCList             link;
@@ -1727,17 +1731,17 @@ struct JSContext
     /* Temporary arena pool used while evaluate regular expressions. */
     JSArenaPool         regExpPool;
 
     /* Top-level object and pointer to top stack frame's scope chain. */
     JSObject            *globalObject;
 
     /* State for object and array toSource conversion. */
     JSSharpObjectMap    sharpObjectMap;
-    js::HashSet<JSObject *> busyArrays;
+    js::BusyArraysMap   busyArrays;
 
     /* Argument formatter support for JS_{Convert,Push}Arguments{,VA}. */
     JSArgumentFormatMap *argumentFormatMap;
 
     /* Last message string and log file for debugging. */
     char                *lastMessage;
 #ifdef DEBUG
     void                *logfp;
@@ -2128,19 +2132,16 @@ struct JSContext
   private:
     /*
      * The allocation code calls the function to indicate either OOM failure
      * when p is null or that a memory pressure counter has reached some
      * threshold when p is not null. The function takes the pointer and not
      * a boolean flag to minimize the amount of code in its inlined callers.
      */
     JS_FRIEND_API(void) checkMallocGCPressure(void *p);
-
-    /* To silence MSVC warning about using 'this' in a member initializer. */
-    JSContext *thisInInitializer() { return this; }
 }; /* struct JSContext */
 
 #ifdef JS_THREADSAFE
 # define JS_THREAD_ID(cx)       ((cx)->thread ? (cx)->thread->id : 0)
 #endif
 
 #if defined JS_THREADSAFE && defined DEBUG