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
pageNumber - 1
    );
    if (pageView && thumbnailView) {
      thumbnailView.setImage(pageView);
    }
  }
  if (error) {
    PDFViewerApplication.l10n
      .get(
        "rendering_error",
        null,
        "An error occurred while rendering the page."
      )
      .then(msg => {
        PDFViewerApplication.error(msg, error);
      });
  }
  PDFViewerApplication.externalServices.reportTelemetry({
    type: "pageInfo",
    timestamp,
  });
  
  PDFViewerApplication.pdfDocument.getStats().then(function (stats) {
    PDFViewerApplication.externalServices.reportTelemetry({
      type: "documentStats",
      stats,
    });
  });
}
function webViewerPageMode({ mode }) {