I believe Firefox Focus (on Android and iOS) uses the OS native web view (effectively, Chrome or Safari), but the actual Firefox for Android uses Gecko.
^ This seems right from my quick googling, there is this project for a gecko webview, which needs work: https://wiki.mozilla.org/Mobile/GeckoView and mentions firefox focus' gecko build option.
Firefox on android is too slow to use a lot of times. Something mozilla should be able to do better.
