With the release of their Cloud Reader browser app for Kindle, Amazon has become the first of the major booksellers to respond to Apple's recent enforcement of its rules on in-app purchase with an attractive browser-based alternative.

The Cloud Reader currently works with the Chrome and Safari browsers only, and - perhaps curiously - on the iPad but not the iPhone. With the ability to read offline, and to add a homescreen shortcut, this seems on first impressions to offer a very slick user experience, definitely comparable to the native app. More importantly, so far as Amazon is concerned, it also reinstates the link to the Kindle store that was recently removed from the Kindle iOS app in order to conform to Apple's rules on in-app purchase. Though the transition from reading to buying isn't yet seamless - the navigation toolbars suppressed within the reader reappear when you move to the store, and there's no obvious way to return to the reader - it's certainly easier than reaching the Kindle store via the native Kindle app.

So how will Apple respond? I've been wondering whether they might remove the option for websites to add a shortcut to users' homescreens via Safari. This functionality allows webapps to mimic the smoothness and convenience of native apps by hiding browser toolbars and making them available via a single tap of an icon. By removing this option for all websites, Apple would redraw the divide between native apps and webapps and - most importantly - damage sales of ebooks from the Kindle store, sales from which they take no percentage. Not only would the Cloud Reader webapp be less visible without its homescreen shortcut, but every click you add to the purchasing process halves the chances of completing a sale. If Apple were to remove this homescreen shortcut functionality, it would add only one click to the purchase process, but that could still impact signficantly on Kindle ebook sales.

Apple, of course, will not be the only player to respond to Amazon's move. Kobo is said to be developing its own HTML5 webapp, and others will certainly follow. The next phase of the battle for ebook market dominance is upon us.