@
RunamuckRez
All you need to do is to connect your Kindle Fire to your computer with a microUSB cable,
Then use Windows Explorer "assuming that you are running windows" and move the mobi books to the Books folder on your Kindle Fire's sdcard.
This is called sideloading.
If you have WiFi, then you can get an app, WiFi File Explorer Pro at the Kindle Store and tether to your Kindle Fire through WiFi.