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
pageIdsToKeep.add(pagesToKeep[i].id);
      }
      moveToEndOfArray(data, function (page) {
        return pageIdsToKeep.has(page.id);
      });
    }
    while (data.length > size) {
      data.shift().destroy();
    }
  };
  this.has = function (view) {
    return data.includes(view);
  };
}
function isSameScale(oldScale, newScale) {
  if (newScale === oldScale) {
    return true;
  }
  if (Math.abs(newScale - oldScale) < 1e-15) {
    
    
    return true;
  }
  return false;
}
/**
 * Simple viewer control to display PDF content/pages.
 * @implements {IRenderableView}
 */
class BaseViewer {