diff --git a/js/src/xpconnect/src/xpcjsruntime.cpp b/js/src/xpconnect/src/xpcjsruntime.cpp
index f13d01d358c..d9ad3a21452 100644
--- a/js/src/xpconnect/src/xpcjsruntime.cpp
+++ b/js/src/xpconnect/src/xpcjsruntime.cpp
@@ -1329,6 +1329,10 @@ struct PRInt64Data {
     PRInt64 n;
 };
 
+// This function is miscompiled with MSVC 2005 when PGO is on.  See bug 664647.
+#ifdef _MSC_VER
+#pragma optimize("", off)
+#endif
 void
 GetJSObjectSlotsCallback(JSContext *cx, void *v, size_t traceKind, void *thing)
 {
@@ -1339,6 +1343,9 @@ GetJSObjectSlotsCallback(JSContext *cx, void *v, size_t traceKind, void *thing)
         data->n += obj->numSlots() * sizeof(js::Value);
     }
 }
+#ifdef _MSC_VER
+#pragma optimize("", on)
+#endif
 
 static PRInt64
 GetJSObjectSlots(void *dummy)
@@ -1359,6 +1366,10 @@ GetJSObjectSlots(void *dummy)
     return data.n;
 }
 
+// This function is miscompiled with MSVC 2005 when PGO is on.  See bug 664647.
+#ifdef _MSC_VER
+#pragma optimize("", off)
+#endif
 void
 GetJSStringCharsCallback(JSContext *cx, void *v, size_t traceKind, void *thing)
 {
@@ -1367,6 +1378,9 @@ GetJSStringCharsCallback(JSContext *cx, void *v, size_t traceKind, void *thing)
     PRInt64Data *data = (PRInt64Data *) v;
     data->n += str->charsHeapSize();
 }
+#ifdef _MSC_VER
+#pragma optimize("", on)
+#endif
  
 static PRInt64
 GetJSStringChars(void *dummy)
@@ -1592,9 +1606,8 @@ XPCJSRuntime::XPCJSRuntime(nsXPConnect* aXPConnect)
         NS_RegisterMemoryReporter(new NS_MEMORY_REPORTER_NAME(XPConnectJSGCHeap));
         NS_RegisterMemoryReporter(new NS_MEMORY_REPORTER_NAME(XPConnectJSStack));
         NS_RegisterMemoryReporter(new NS_MEMORY_REPORTER_NAME(XPConnectJSScripts));
-        // XXX: these two are disabled due to crashes.  See bug 664647.
-        //NS_RegisterMemoryReporter(new NS_MEMORY_REPORTER_NAME(XPConnectJSObjectSlots));
-        //NS_RegisterMemoryReporter(new NS_MEMORY_REPORTER_NAME(XPConnectJSStringChars));
+        NS_RegisterMemoryReporter(new NS_MEMORY_REPORTER_NAME(XPConnectJSObjectSlots));
+        NS_RegisterMemoryReporter(new NS_MEMORY_REPORTER_NAME(XPConnectJSStringChars));
 #ifdef JS_METHODJIT
         NS_RegisterMemoryReporter(new NS_MEMORY_REPORTER_NAME(XPConnectJSMjitCode));
         NS_RegisterMemoryReporter(new NS_MEMORY_REPORTER_NAME(XPConnectJSMjitData));