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
}
    if (x_ <= p / q) {
      c = p;
      d = q;
    } else {
      a = p;
      b = q;
    }
  }
  let result;
  
  if (x_ - a / b < c / d - x_) {
    result = x_ === x ? [a, b] : [b, a];
  } else {
    result = x_ === x ? [c, d] : [d, c];
  }
  return result;
}
function roundToDivide(x, div) {
  const r = x % div;
  return r === 0 ? x : Math.round(x - r + div);
}
/**
 * Gets the size of the specified page, converted from PDF units to inches.
 * @param {Object} An Object containing the properties: {Array} `view`,
 *   {number} `userUnit`, and {number} `rotate`.
 * @returns {Object} An Object containing the properties: {number} `width`
 *   and {number} `height`, given in inches.
 */
function getPageSizeInches({ view, userUnit, rotate }) {