This is a new privacy-enhanced browser for Android, based on Mozilla Firefox, configured by default to work with Orbot: Tor for Android.
You can find the source information on building "Fennec" for Android (aka Firefox) from source here: https://wiki.mozilla.org/Mobile/Fennec/Android#Building_Fennec
Review the "Orfox Spec" document in this repo for more information on the design goals and defaults for this browser.