Amazon clearly didn't have any problems generating a profit this holiday. The online retail powerhouse says that it made a tidy profit of $239 million in the fourth quarter of 2013, or more than twice as much as it managed a year earlier. That's on top of a year-over-year revenue increase, to boot -- Amazon raked in $25.59 billion during the quarter versus $21.27 billion at the tail end of 2012. The only sour note is a full-year profit of just $274 million, although that's still much better than the $39 million loss from 2012. The company hasn't said just why it did so well, although we wouldn't be surprised if the Kindle Fire HDX launch and a recently introduced Sunday delivery option played important roles.