Android devices are a bit trick as you might need root access to any hidden system files of firebox browser so you maybe force to first have to root the device which is one long stressful process.
Try asking for help from the Mozilla community; https://support.mozilla.org/en-US/questions/new/mobile
This is helpful mate, I just hope so that Mozilla community will promptly accommodate my concerns since they're not focused on one problems only. However if given small chances, my account in metamask extension would be accessed as well. Thanks for the help as well as with other great members here in this forum, and I recommend this thread will be locked because my concern is now answered.