On our return from Shannon Airport to JFK, we were surprised/pleased to go through U.S. customs/immigration in Ireland BEFORE boarding. Never had this experience before, and we were so happy to just pick up our bags and go once we arrived at JFK.
We've been traveling south out of DC area the last few years so this is completely new for us. Never flew from JFK.
My question is : How common is this? Does LHR have this? It's great!