Evenscroll от Steven Lee

Features:
- An additional scrollbar appears on the right side of the webpage you are viewing; drag the thumb to scroll the webpage at ease, no matter how long the page is.
- Hover on the thumb to scroll the whole screen at a time with your mouse wheel.
- Middle-click on the thumb to go to the page bottom.
- Right-click on the thumb to navigate back to the page top.
- Double-click on the thumb to hide the default scrollbar.
- Buttery smooth transitions, especially on high refresh rate monitors.
- Movements are interruptible by moving the cursor out of the thumb.

• This additional scrollbar only appears on webpages longer than 3 screens in height.