str = dont_AddRef(NS_STATIC_CAST(nsISupportsString*, mPropertyTable->Get(&key)));
str = dont_AddRef(NS_STATIC_CAST(nsISupportsWString*, mPropertyTable->Get(&key)));
nsPresState::GetStateProperty(const nsString& aName, nsString& aResult){  // Retrieve from hashtable.  nsCOMPtr<nsISupportsString> str;  nsStringKey key(aName);  if (mPropertyTable)    str = dont_AddRef(NS_STATIC_CAST(nsISupportsString*, mPropertyTable->Get(&key)));     if (str) {    char* data;    str->GetData(&data);    aResult = data;    nsAllocator::Free(data);  } else {    aResult = "";  }  return NS_OK;}