Welcome to the Roku Community, @FusionFiery!
Thank you for contacting us regarding the setup of your Roku remote and the use of the headphone mode on Fire TV. We appreciate your interest and would like to clarify that the Roku remote is designed specifically for use with the Roku interface.
As Roku and other non-Roku streaming devices operate on different operating systems, the remote's compatibility is limited to Roku devices only.
If you have any further questions or need assistance, please feel free to ask!
Thanks,
Jharra
Jharra Q.
Roku Community Moderator