why not use perfect viewer? my understanding is that it is free although you can donate if you wish. Actually from the dev's page:
> License
>Perfect Viewer is free software.
>You can use Perfect Viewer on any Android-powered devices, including a device in a commercial organization. You don't need to register or pay for Perfect Viewer.
Here is the dev's page where you can download it for yourself if you want to give it a try.
I tried loading cbr and cbz files and the fire doesn't notice them. So then i tried making a mobi file of a comic once but the images came out distorted. My suggestion is to just use a comic reader.