This is taken directly from source with no modifications.
Firefox Focus for Android
Browse like no one’s watching. The new Firefox Focus automatically blocks a wide range of online trackers — from the moment you launch it to the second you leave it. Easily erase your history, passwords and cookies, so you won’t get followed by things like unwanted ads.
For more information please see the following links:
Updated as of: March 3rd, 2018
As of now there is no longer a Gecko version. Also, the Beta version requires the APK to be signed which I cannot do, so it's back to debug builds.
WebView Universal Debug version:
Klar (German language) WebView Universal Debug version:
Focus by Firefox, App for all devices (see above for details)
Source Code: https://github.com/mozilla-mobile/focus-android
Last Updated 2018-03-03