You can install MEGA IPTV on Amazon Fire Stick by downloading the app called "Downloader" and type apk.mega-iptv.app in the URL field.
At the moment we do not have a dedicated feature for adding channels to favorite but we have an automatic saving feature for most wached TV channels, which is a good alternative to "Favorites".
The default code is 0000.
On Samsung and LG devices there is a dedicated Yellow KEY on the remote control which you can use in the TV Channels list if your playlist provider offers this feature.
On Android devices you must press and hold "OK" or "ENTER" key for 3 seconds on the remote control.