This problem applies to all the documents that I have ever opened.

Configuration:
- Web browser and its version: Google Chrome 83.0.4103.61 , also Firefox 76.0.1
- Operating system and its version: Win 7 x64
- PDF.js version: 2.3.164 version of extension
- Is a browser extension: yes

Steps to reproduce the problem:
1. Select any "Spreads" mode of view. Or "No spreads", but wrapped scrolling mode - doesn't matter. 
2. Select "Page Fit" zoom mode. We should get several pages per screen
3. Try to scroll document by any of keys: Page Down, n, j, Space Bar

I expect to see the next group of pages (for example, if there are 5 pages on the screen, I expect to see the next 5 pages)

What went wrong? Scrolling goes one page at a time, so if I have 5 pages on the screen, nothing happens when I pressed Page Down 5 times . For the 6th time I finally see the next group of pages.

Just for example: Adobe Reader scrolls properly in two-page mode, 2 pages at once. 

P.S. Sorry for my English, I hope I correctly stated the essence of the problem
(skipOverflowHiddenElements &&
      getComputedStyle(parent).overflow === "hidden")
  ) {
    if (parent.dataset._scaleY) {
      offsetY /= parent.dataset._scaleY;
      offsetX /= parent.dataset._scaleX;
    }
    offsetY += parent.offsetTop;
    offsetX += parent.offsetLeft;
    parent = parent.offsetParent;
    if (!parent) {
      return; 
    }
  }
  if (spot) {
    if (spot.top !== undefined) {
      offsetY += spot.top;
    }
    if (spot.left !== undefined) {
      offsetX += spot.left;
      parent.scrollLeft = offsetX;
    }
  }
  parent.scrollTop = offsetY;
}
/**
 * Helper function to start monitoring the scroll event and converting them into
 * PDF.js friendly one: with scroll debounce and scroll direction.
 */
function watchScroll(viewAreaElement, callback) {