Just how much money does Amazon generate from selling its Kindle eReaders and tablets? It’s tough to say because Amazon never releases specific sales figures for its devices. AllThingsD points us to new research from Morgan Stanley that estimates Amazon will sell $4.5 billion worth of Kindle-branded devices this year, a 26% increase from 2012. The Morgan Stanley researchers also think that Kindle sales will total $5 billion next year and $5.5 billion in 2015. Amazon will release the next generation of its 7-inch Kindle Fire this fall and its specs will include a 1,920 x 1,200-pixel display,¬†a 1.5GHz dual-core Texas Instruments¬†OMAP4 4470 processor with PowerVR SGX544 graphics, 1GB of RAM and Android 4.2.2 Jelly Bean. Second-generation Kindle Fire HD tablets are also in the works, and they feature some of the most impressive tablet specs we have ever seen.