FF4 installation using Google chrome web browser
https://www.jargonsoft.com/ff4.apk
or
scan the QR code:
Instructional video:
https://www.youtube.com/watch?v=YQsagHahCxs&feature=youtu.be
Shows how to use Google Chrome browser to download and install FF4.
Example showing manual URL entry as well as scanning QR code.
Illustrates what to do if Google Chrome acts strangely.