Is it illegal to jailbreak a Firestick?
It is not illegal to jailbreak a Fire TV Stick. The only difference between a regular Fire TV Stick and a jailbroken one is the installation of KODI. Its legality depends on how you use the device. … This is done through 3rd party Kodi-Plugins that provide access to pirated/unlicensed content.

Reference:
Is It Illegal to Jailbreak a Fire Stick | Grounded Reason
May 2, 2019