Add a max speed setting for dragging

[davidparsson]

[ostrich]

To this point, I think it would be nice to have a toggle to allow the user to switch between Scrollbar Anywhere style scrolling (constant scroll speed relative to the scroll bar) and Wet Banana style scrolling (constant scroll speed relative to mouse speed).

I started out using Scrollbar Anywhere on Firefox and then switched to Wet Banana, and after a little while I found myself thinking that Wet Banana style scrolling is more logical and more usable. Wet Banana itself, however, is too buggy and development seems to have stagnated.