With Amazon set to release its fourth quarter—and year end—results Tuesday afternoon Stifel Nicolas analyst Jordan Rohan estimates that the company sold 6 million Kindle Fire tablets in the fourth quarter. Rohan had previously put the number sold at 5 million units. Rohan believes the strong performance of the Fire will provide Amazon with ongoing benefits by increasing the amount of content, including e-books, that new Fire owners will buy. As a result he has upped his revenue forecast for 2012 by over $2 billion to a total of $67 billion. And while Amazon is making no money on the Fire, Rohan notes that as more customers buy digital content, Amazon’s margins could improve because of lower shipping costs.