Hi, just updated Mangle to 0.2. I've fixed several bugs:
Page back now moves one page only.
You can use shift+page navigation buttons to change chapters.
Workaround for another framework bug which caused the spinny progress thing to disappear when you run mangle.
Auto-resize images on orientation change.
It is available from here. If you've already rooted+installed my developer keys, all you need to do is unzip it onto your kindle over USB. If you're installing for the first time, please see here for instructions.