EasyScroll

This extension provides the ability to scroll smoothly using drag motion. Better accessibility for developers who prefer smooth scrolling for the visual continuity (instead of the snappy PgUp/PgDown/ScrollUp/ScrollDown motion)

• Hold MiddleClick to scroll vertically through the document
• Hold Shift with MiddleClick to scroll both vertically & horizontally at the same time

Go to Tools > Options > EasyScroll to edit the scroll amount