Apple became the world’s most valuable company for a brief period yesterday, overtaking Exxon whose value had dipped on the back of the depressed oil prices. Those two should continue to duke it out as Apple posts record results, and oil prices inevitably rise. However, Apple’s celebrations may have been short-lived as Amazon came up with a clever way to circumvent their rules on in-app purchases. Today, Amazon released the Kindle Cloud Reader. Essentially, this is a snazzy version of the Kindle reading app, but the key difference is that it’s browser-based. This means that iPad owners will be able to read books, and browse for new purchases, all in the same web-based program.