Amazon is releasing a free software update to all Kindle Fire users over the next few days. The over-the-air update will upgrade the devices from version 6.2.2 to version 6.3. A downloadable upgrade file is also available on the site for the eager.

Most of the updates involve enhanced reading features and extras. Amazon says its latest upgrade will also include "faster re-connect of WiFi after Kindle Fire has been asleep, and general performance enhancements." Amazon has been vague about what specifically those general performance enhancements might entail.

Users of version 6.3 will have the ability to share passages from a book by highlighting a passage and choosing "share" within the book's toolbar. These shared passages will be available to other Kindle readers perusing the same book, and passages can be shared on Facebook and Twitter as well. Sharing passages is a feature that regular Kindle owners can already do, so this feature simply incorporates Kindle Fire.

Amazon is also bringing "Book Extras" to its books. It's an application powered by Shelfari, an Amazon-owned wiki for books. Version 6.3 will allow users to access Shelfari discussions, character descriptions, glossaries of terms, and other information about the book from within the book. That update should prove quite helpful if you like 19th century Russian novels.

Although the new update obviously won't deliver your Fire any more storage than the dinky 6GB (or so) it already has, Fire users will also be able to buy a large selection of print replica textbooks (which preserve the layout, text, and coloring of textbooks without being transferred to e-book confusion). Also, Amazon's Whispersync will now be available to archive personal documents in the cloud for re-download any time.

The update also means the rental period for movies on a Kindle Fire will start when the user starts watching the movie, not when the movie is downloaded.

Finally, a reading view for Amazon Silk will be available. Amazon claims it will load the body of any Web page in a single-screen view, even if it's a multi-page article, an allow the user to toggle back and forth between the original content and the reading view.