This userscript is designed for mobile browsers to scroll page on double tap.

Scroll up – Double tap in top half of the screenScroll down – Double tap in bottom half of the screenFast scrolling – Double tap and start moving your finger before lifting on a second tap (can be disabled by fastScrollingEnabled variable)

Only double taps on empty space are recognized, e.g. if you double tap on link, image or button, they will consume the event and will be clicked.