Wow, this thing is weird.
Firefox Focus is a free and open-source privacy-focused browser from Mozilla, available for Android[2][3] and iOS smartphones and tablets.[4][5] Firefox Focus was initially a tracker-blocking application for mobile iOS devices, released in December 2015.[6] It was developed into a minimalistic web browser shortly afterwards.[7] However, it can still work solely as a tracking-blocker in the background of the Safari browser on Apple devices.
In June 2017, the first release for Android went public and was downloaded over one million times in the first month.[8] As of January 2017, it is available in 27 languages.[9] Since July 2018, Firefox Focus is preinstalled on the BlackBerry Key2 as part of the application Locker .[10][11]
To bypass content-blocker restrictions from Apple, Firefox Focus is using the UIWebView-API on iOS devices.[12][13] On Android, it has been using the Blink engine in version 6.x or earlier, and GeckoView since version 7.0.[14]
It’s like an ad-blocker that is basically a minimal web browser to do it’s job, so they made it one on it’s own… and then ported it to Android. 