The Amazon Kindle Fire comes with auto-orientation enabled by default. So whenever you rotate or roll the device, its internal accelerometer and gyroscope compensate by rotating the screen contents.
I’ve found this feature to be annoying when laying down to read from the device. Here’s how to disable the feature.
Tap the settings notification bar at the top right of the Kindle Fire home screen. From the drop-down menu, tap the Unlocked button so it says locked. Auto-orientation is now disabled.
Note: This will lock the screen orientation to its current setting. To rotate the screen again you’ll need to unlock the setting.