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
: div.offsetTop + div.clientTop + div.clientHeight
        );
      }, 0);
      
      
      
      
      for (let i = -size; i < size; i += 7) {
        
        
        
        for (let j = i + 5; j < size; j += j - i) {
          const scrollEl = horizontal
            ? {
                scrollTop: 0,
                scrollLeft: i,
                clientHeight: 10000,
                clientWidth: j - i,
              }
            : {
                scrollTop: i,
                scrollLeft: 0,
                clientHeight: j - i,
                clientWidth: 10000,
              };
          expect(
            getVisibleElements({
              scrollEl,
              views: pages,
              sortByVisibility: false,