nsCStringKey key(prop); if (!Exists(&key)) return NS_ERROR_FAILURE;
nsProperties::SetProperty(const char* prop, nsISupports* value){    nsCStringKey key(prop);    if (!Exists(&key))        return NS_ERROR_FAILURE;    nsISupports* prevValue = (nsISupports*)Put(&key, value);    NS_IF_RELEASE(prevValue);    NS_IF_ADDREF(value);    return NS_OK;}