[Kindle Fire Android Development] chrisliphart:
Straight off of Amazon's server. Figured the devs can start playing with this. :)

http://kindle-fire-updates.s3.amazonaws.com/update-kindle-6.3_D01E_4019920.bin

Only use this if you want to go completely stock. You will loose CWM/TWRP and root if you install this.

Pretty much devs only on this one.

EDIT: Root has been achieved by jcase: http://xdaforums.com/showthread.php?t=1568340

You can also install the ROM pre-rooted from eldarerathis: http://xdaforums.com/showthread.php?t=1569298

New Features (from the Coming Soon section on Amazon's site):

Sharing: Customers will be able to easily share favorite passages and notes from their books directly from Kindle Fire, without even leaving the book. Customers simply highlight a passage and select "Share" or choose the "Share" option from the toolbar within a book, write a note if they choose, and select which social network to share with. Passages or notes a customer chooses to share will be displayed to other Kindle readers viewing the same book, and customers can also choose to share via Facebook and Twitter. Amazon already has a vibrant community of readers who choose to share favorite passages and notes from their reading through Kindle.amazon.com. This update brings these notes and highlights to Kindle Fire, so a reader can easily see what other readers are saying about their books.

Book Extras: Powered by Shelfari, Amazon's community of book lovers, Book Extras make it easy for customers to see supplemental material about the book they are reading, without even leaving the book. Customers can view descriptions of characters, a glossary of common terms used in the book, information on the authors and common locations referenced in the book, and more. To view Book Extras from within a book, customers simply tap the top of the screen to bring up the toolbar, tap the menu button and select "Book Extras."

Archive of Personal Documents: Customers' personal documents will be stored in the Amazon Cloud and available for re-download at any time from the Documents tab on Kindle Fire. Just as with Kindle books, Whispersync will automatically sync notes, highlights and last page read for personal documents.

Print Replica Textbooks: Students can buy thousands of print replica textbooks to read on their Kindle Fire and save up to 60% off the list price of the print textbook. Print replica textbooks maintain the rich formatting, color and layout of the print editions, with features including notes and highlights, zoom and pan, linked table of contents, real page numbers and whispersync of notes, highlights and last page read.

Reading View for Amazon Silk: There is a seemingly endless array of interesting and engaging content available on the Internet. Sometimes, unfortunately, that business article, blog post, or sports recap you clicked on is surrounded by a host of competing material. With Reading View on Silk, the content that you're interested in is elevated above the clutter. When invoked by the customer, Silk will load the body of the page in a reading-optimized, single screen view (even for multi-page articles). The full page is still available in the background, allowing the reader to easily toggle back to a traditional view to see other interesting features on the page.

Movie Rentals: The rental period for movie rentals that are downloaded to Kindle Fire now starts when a customer starts watching the movie, rather than when a customer starts downloading the movie.

Additional Enhancements: This update will also bring some of the features customers have requested, including faster re-connect of Wi-Fi after Kindle Fire has been asleep, and general performance enhancements.