There is a minor issue, that some rooted Fire TV owners are encountering, where they are unable to access the /sdcard and other directories while in su mode. The issue is caused by a namespace separation setting within the SuperSU app. Normally, you would launch the app and change the setting to resolve the issue, but since the SuperSU app is installed as a system app in rbox’s pre-rooted ROMs, you cannot open SuperSU to make the necessary changes. Thankfully rbox is on top of things. He has released a flashable zip, which you can find at the top of this thread or download directly here, that fixes the issue from within TWRP. So, if you, or an app you’re using, ever have trouble moving, copying, or accessing files from a directory while in su mode, but have no trouble while not in su mode, then you need to download the flashable zip and install it from within TWRP using this guide. The procedure to install the zip is identical to installing a pre-rooted ROM. Doing so will correct the namespace setting and allow you to access directories on a rooted Fire TV correctly.