Hi

I am sorry, but Firefox for Android is not available for Amazon Fire devices.

It is not available as in not listed on the Amazon app store. Mozilla did have Android Firefox on Amazon app store long ago but Amazon was found to modify the file which cause issues with updates if I recall so Mozilla pulled it since Amazon was not willing to change on doing that.

You may be able to side load install the Firefox apk file though. Fenix is the code name for Android Firefox.

https://archive.mozilla.org/pub/fenix/releases/145.0.1/android/

If you have a pretty current tablet then try the fenix-145.0.1-android-arm64-v8a/