Hello,
You can customize scrolling settings in the Options page - by default it simulates scrollbar, if you want constant speed, change it to Grab and Drag style.
Regarding performance - there is not much I can do, complex pages like Facebook or Twitter are too much resource consuming and scrolling won't be that smooth even on fast PC. But there is some special option in the Options page / Advanced / Performance that you could try.

Have a nice weekend :)

Best regards,
Juraj Mäsiar