I pointed out how that happens already though. Firefox uses middle-click to direct a widgety thing to move the viewport. Other documents use middle click and drag to move the document. The same hand motion will move in two entirely opposite directions. I know some people get really (like REALLY) hung up on this though, and understand that. I just view it as another abstraction I get to move through.
(Also, for me its two entirely different physical movements of grabbing the scrollbar vs scrolling with two fingers, so I don’t even notice. In one, I use middle and ring to move a document around. Another, I’m moving the mouse with a single finger, and then pressing down directly or using my thumb to click and then moving the finger.)