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 learn more about the design of Tor Browser here: https://www.torproject.org/projects/torbrowser/design/
Review the "Orfox Spec" document in this repo for more information on the design goals and defaults for this browser.
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
Additionally, it is easiest to build when using a specific Android SDK setup to make sure that the version of things are correct, like the Support libs.
cd /opt
wget https://dl.google.com/android/android-sdk_r24.3.4-linux.tgz
tar xzf android-sdk_r24.3.4-linux.tgz
export ANDROID_HOME=/opt/android-sdk-linux
export PATH="$ANDROID_HOME/tools:$PATH"
android update sdk --no-ui --filter tools,platform-tools,build-tools-23.0.1,android-22
cd $ANDROID_HOME
mkdir -p extras/android
cd extras/android
wget https://dl.google.com/android/repository/support_r22.2.1.zip
unzip support_r22.2.1.zip
chmod -R a+rX $ANDROID_HOME
find $ANDROID_HOME -executable |xargs chmod a+x