Also seeing it in Full Screen (F11) helps. That’s what I need (I personally use it always anyway) to see the button in standard zoom.
Scroll bar in FF seems to not be working correctly in standard zoom - doesn’t allow full scroll and showing this button whereas on Opera scroll bar seems to be giving more freedom and allows to see the button. But when you zoom some more it’s ok:
At 100% zoom (non-fullscreen):
A bit more zoom (non-fullscreen):
