=X=, you pretty much nailed it, we made the app to iPhone-ish, and we're learning to fix that now. In particular, we are changing the back button functionality so that it will pop you out of the app like a regular Android app does. That fix should be available as an update from the android market early next week.
Thanks for the note about .acsm issue on Dropbox/Astro. We will look at them and see if there is a way open them. As Tomsem noted, if you fulfill the book using ADE first and then drop it into dropbox, you can easily open it in Bluefirereader from the popup menu.
As for being able to open .acsm files in the browser, unfortunately this is appears to be a bug in the Android browser itself. It has been filed under Issue 17205. If anyone who is having this issue wants to
look it up and star it, that may help to expedite the process of fixing it.