I've been pestering Amazon and Roku and Samsung (smart tv) for ebook readers annually since 2012. They aren't interested. Amazon's Cloud Kindle only recognizes 4 web browsers and that doesn't even include Microsoft Edge.
For a workaround, I have hooked up a $35 Raspberry Pi computer, loaded it with the standard Raspbian OS (Linux) and added Iceweasel (Firefox for Linux). Using Iceweasel, you can log into your Cloud Kindle account (https://read.amazon.com
) and read your ebook in the browser. If you want, you can even download the entire book you're currently reading and set the browser to NOT clear data when you log out.
Then, when you reboot the Pi and restart Iceweasel, you can use "Work offline" mode (maybe while traveling away from your last wi-fi access) and continue reading your ebook right where you left off. Note: reading the books this way does not require either a Kindle or iOS device or a ROKU.
The Raspberry Pi computer, itself, is only $35, but to make it useful, you need some extra things. You can buy "Starter kits" with all the extra things (HDMI cable, mouse & keyboard, SD card with OS, power supply, etc) for prices from $59 on up, depending on what extras you want. You will need to supply your own monitor. Still worth it. The latest model Raspberry Pi 3 has a 1.2GHz quad core CPU and 1GB ram and can accept a 32GB SDcard and can output 1080P, 30fps videos just fine through it's HDMI connector.
I've hooked one onto our 50" LED TV in the living room to work around the fact that the TV manufacturers just don't want to bother with ebooks on their TV's. I can also use it to do anything else a basic computer can do, except for power gaming.
The Raspberry Pi's can also be used to run KODI, either by swapping out the SDcard or you can install KODI on top of Raspbian.
Meanwhile, in the years since we got our 2012 Samsung Smart TV, Amazon has only added their music store. Amazon videos can only be watched if you have the Amazon prime account.
I use the Raspberry Pi's and KODI and watch any darn thing I please. CoolReader and Calibre also can be run on the Raspberry Pi's and used with your ebooks directly.
Calibre on your PC can be used with add-ons to remove DRM from Kindle books you purchased legally and convert them to EPUB format you can then put on your Raspberry Pi and read with either CoolReader or Calibre.