Mozilla did get Firefox on Amazon App store for a short time as of version 9.0 however it was soon found out that Amazon modified and resigned the package and caused update problems as a result. This has not been resolved since. You may still be able to side load the apk though the Android Firefox is not made with Fire OS based on Android in mind. https://github.com/mozilla-mobile/fenix/releases Old article https://support.mozilla.org/en-US/kb/installing-firefox-android-amazon-kindle-fire