Hello Sofia,
This addon is meant to be used with a mouse. So if you use touchpad on your Mac, then it's not gonna be useful.
If you do have mouse, make sure to visit Options page where you can setup what mouse button is used for scrolling and where you can test the scrolling (in the right area).
If you have more questions, you can contact me directly on my support email.
Best regards,
Juraj Mäsiar