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
let minIndex = 0;
  let maxIndex = items.length - 1;
  if (maxIndex < 0 || !condition(items[maxIndex])) {
    return items.length;
  }
  if (condition(items[minIndex])) {
    return minIndex;
  }
  while (minIndex < maxIndex) {
    const currentIndex = (minIndex + maxIndex) >> 1;
    const currentItem = items[currentIndex];
    if (condition(currentItem)) {
      maxIndex = currentIndex;
    } else {
      minIndex = currentIndex + 1;
    }
  }
  return minIndex; 
}
/**
 *  Approximates float number as a fraction using Farey sequence (max order
 *  of 8).
 *  @param {number} x - Positive float number.
 *  @returns {Array} Estimated fraction: the first array item is a numerator,
 *                   the second one is a denominator.
 */
function approximateFraction(x) {