Works great so far! Thanks! So far I was using "Grab and drag", but sadly it does not support Firefox 57+ at the moment. Luckily, I found your add-on and it's nice that it has virtually the same capabilities.

I have a suggestion that you may implement in a future version:

When a page is being scrolled up or down with the infinite momentum enabled, it will be helpful if we can dynamically control the speed of the momentum by rotating the mouse wheel (scroll wheel) up or down. Example: If we scroll the page so that we see the content from top to bottom direction (scroll bar goes from top to bottom), rotating the mouse wheel upwards will decrease the momentum speed depending on how many "steps" of wheel rotation where used, while rotating the mouse wheel downwards will increase the momentum speed. This could be optional so that people don't get upset with the changes to something they already got used in the past. Also, it will be nice if the upwards/downwards action can be reversed, because some people may prefer to increase or decrease the momentum the reverse way. A left-click, middle-click or right-click will stop the movement of the page.