--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -4408,16 +4408,20 @@ JS_LookupPropertyWithFlagsById(JSContext
 
 struct JSPropertyDescriptor {
     JSObject           *obj;
     unsigned           attrs;
     unsigned           shortid;
     JSPropertyOp       getter;
     JSStrictPropertyOp setter;
     jsval              value;
+
+    JSPropertyDescriptor() : obj(NULL), attrs(0), shortid(0), getter(NULL),
+                             setter(NULL), value(JSVAL_VOID)
+    {}
 };
 
 /*
  * Like JS_GetPropertyAttrsGetterAndSetterById but will return a property on
  * an object on the prototype chain (returned in objp). If data->obj is null,
  * then this property was not found on the prototype chain.
  */
 extern JS_PUBLIC_API(JSBool)

--- a/js/xpconnect/wrappers/AccessCheck.cpp
+++ b/js/xpconnect/wrappers/AccessCheck.cpp
@@ -409,17 +409,16 @@ ExposedPropertiesOnly::check(JSContext *
         return false;
     }
 
     JSObject *hallpass = &exposedProps.toObject();
 
     Access access = NO_ACCESS;
 
     JSPropertyDescriptor desc;
-    memset(&desc, 0, sizeof(desc));
     if (!JS_GetPropertyDescriptorById(cx, hallpass, id, JSRESOLVE_QUALIFIED, &desc)) {
         return false; // Error
     }
     if (!desc.obj || !(desc.attrs & JSPROP_ENUMERATE))
         return false;
 
     if (!JSVAL_IS_STRING(desc.value)) {
         JS_ReportError(cx, "property must be a string");

--- a/js/xpconnect/wrappers/ChromeObjectWrapper.cpp
+++ b/js/xpconnect/wrappers/ChromeObjectWrapper.cpp
@@ -67,32 +67,30 @@ ChromeObjectWrapper::has(JSContext *cx, 
     if (!JS_GetPrototype(cx, wrapper, &wrapperProto))
 	return false;
     if (*bp || !wrapperProto)
         return true;
 
     // Try the prototype if that failed.
     MOZ_ASSERT(js::IsObjectInContextCompartment(wrapper, cx));
     JSPropertyDescriptor desc;
-    memset(&desc, 0, sizeof(desc));
     if (!JS_GetPropertyDescriptorById(cx, wrapperProto, id, 0, &desc))
         return false;
     *bp = !!desc.obj;
     return true;
 }
 
 bool
 ChromeObjectWrapper::get(JSContext *cx, JSObject *wrapper, JSObject *receiver,
                          jsid id, js::Value *vp)
 {
     // Start with a call to getPropertyDescriptor. We unfortunately need to do
     // this because the call signature of ::get doesn't give us any way to
     // determine the object upon which the property was found.
     JSPropertyDescriptor desc;
-    memset(&desc, 0, sizeof(desc));
     if (!ChromeObjectWrapperBase::getPropertyDescriptor(cx, wrapper, id, false,
                                                         &desc)) {
         return false;
     }
 
     // Only call through to the get trap on the underlying object if we'll find
     // something, and if what we'll find is not on a standard prototype.
     vp->setUndefined();