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
};
/**
 * Returns scale factor for the canvas. It makes sense for the HiDPI displays.
 * @returns {Object} The object with horizontal (sx) and vertical (sy)
 *                   scales. The scaled property is set to false if scaling is
 *                   not required, true otherwise.
 */
function getOutputScale(ctx) {
  const devicePixelRatio = window.devicePixelRatio || 1;
  const backingStoreRatio =
    ctx.webkitBackingStorePixelRatio ||
    ctx.mozBackingStorePixelRatio ||
    ctx.backingStorePixelRatio ||
    1;
  const pixelRatio = devicePixelRatio / backingStoreRatio;
  return {
    sx: pixelRatio,
    sy: pixelRatio,
    scaled: pixelRatio !== 1,
  };
}
/**
 * Scrolls specified element into view of its parent.
 * @param {Object} element - The element to be visible.
 * @param {Object} spot - An object with optional top and left properties,
 *   specifying the offset from the top left edge.
 * @param {boolean} skipOverflowHiddenElements - Ignore elements that have
 *   the CSS rule `overflow: hidden;` set. The default is false.
 */
function scrollIntoView(element, spot, skipOverflowHiddenElements = false) {