Okay, so with nydave69’s help, I’ve installed a beta version of the plex player for the firestick tv.
On the firestick, I downloaded the “downloader” app and after allowing third party apps to be installed in the settings, I grabbed the latest version’s (7.30.1.16449-beta) download link from here:
https://forums.plex.tv/t/android-mobile-beta-release-notes/154125/299
and (painfully) typed it into the downloader app on the firestick. Installed and after 1hr of playback, all seems to be good so far.
Thanks!!