The old Firefox 55.0.2 does not have security fixes that later versions have, many of which are critical. Use at your own risk. http://archive.mozilla.org/pub/mobile/releases/55.0.2/

Adobe stopped supporting the ancient Flash Player 11.1.x branch with last version out way back on September 10 2013.

Many websites have long since dropped support of the old 11.1 branch used by Android and BlackBerry Playbook and the old extended support 11.2 version for Linux. So even if you get this old Flash Plugin working in Firefox on Android it may not work for the site(s) you intend to use it on.

A bit surprised that Mozilla took four years to finally drop support of this ancient vulnerable Plugin in Android version of Firefox. I say this because Mozilla does add older versions of Flash Player for desktop to addons.mozilla.org/blocked/ when previous version has critical vulnerabilities (27.0.0.159 and older is currently on list).

https://developer.mozilla.org/en-US/docs/Plugins/Roadmap

This is genuine original on Mozilla site?

There are 3 choices there. Which is the installable program for Android supporting Flash? I still use Firefox 47 so it must be a little better anyway. I really need Flashplayer for work.

Which one works with Android 7?

recDNA said

This is genuine original on Mozilla site?

Of course as only Mozilla has control of the mozilla.org domain.

recDNA said

Which one works with Android 7?

The cpu used in your phone/tablet matters in this case. The x86 is for devices powered by AMD and Intel x86 processors, rather than RISC-based ARM chips for example.