I also would like this feature. My go-to app for reading PDFs and e-books on android, ReadEra, has this option to hide navigation bar and status bar, one tap anywhere on the screen to get them back.
What? You have to be joking? Let me get this right. There is no way to go full screen/ maximize the Firefox browser so we can read pages?
Add it to the list of ways mozilla has fallen much too far behind Edge and Chrome to continue to use. Such a basic necessary function. Lost a day of work because of this insufficiency. Goodbye