This app was mentioned in 7 comments, with an average of 2.00 upvotes
Try this one, it works pretty great for me. Also, if you're keeping the ROMs on an external storage, move it into the internal storage and try again.
To my knowledge the -oid emulators that were popular way back in 1.5-2.x era of Android, have all stopped working or are rather broken from being abandoned.
I've never used a Firestick myself, but I assume most emulators should work the same. I would recommend trying the free options first, there's John NES Lite, Nostalgia.NES, and RetroArch using one of the bnes/FCEUmm/Nestopia/QuickNES cores.