I've been wishing I could do this for a while now, and finally broke out some sniffing tools to see if it could be done. It can, with some caveats.
In Firefox (and probably many other browsers) it is possible to use the ebookstore.sony.com site and buy and download books (downloading does require that Adobe Digital Editions is installed).
You just need to find one of the many available add-ons for changing your user-agent-string, and set it to
Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/532+ (KHTML, like Gecko) ReaderLibrary/3.1
The store is a bit buggy this way, and occasionally throws up error messages (I always get one immediately after logging on), but if you are persistent enough you can do handy things like view your wishlist, or gift certificate balance without having to install the Sony software on all of your PCs.
Presumably the results would be even better on a webkit-based browser.
books does not work with this method, but downloading books bought before does. If a moderator could change the subject, I'd appreciate it.