QLMobi is a plugin for OS X Quick Look feature. It generates previews based on ebook contents, similar to the actual look in the ebook reader. For the thumbnails it uses embedded covers (if present).
It is based on
libmobi library and supports most of the Mobipocket/Amazon formats: prc, mobi, azw, azw3, azw4 and some pdb files.
Source files and the plugin binary may be downloaded from
QLMobi github page.
You just need to move QLMobi.qlgenerator file into ~/Library/QuickLook/ folder to install it for your account, or into (Macintosh HD)/Library/QuickLook/ folder to install it for all users.