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: July 11th, 2018
Focus has switched to full Gecko rendering now - they also have aarch64 and ARM versions, so I have compiled one of each. Builds are debug again due to apk signing!
Downloads can now be found in the "downloads" tab of this project.
And by request, here's a folder for viewing on mobile devices:
Focus by Firefox, App for all devices (see above for details)
Source Code: https://github.com/mozilla-mobile/focus-android
Last Updated 2018-07-13