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
this.pdfViewer.currentPageNumber = val;
  },
  get supportsPrinting() {
    return PDFPrintServiceFactory.instance.supportsPrinting;
  },
  get supportsFullscreen() {
    let support;
    if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("MOZCENTRAL")) {
      support =
        document.fullscreenEnabled === true ||
        document.mozFullScreenEnabled === true;
    } else {
      const doc = document.documentElement;
      support = !!(
        doc.requestFullscreen ||
        doc.mozRequestFullScreen ||
        doc.webkitRequestFullScreen
      );
      if (
        document.fullscreenEnabled === false ||
        document.mozFullScreenEnabled === false ||
        document.webkitFullscreenEnabled === false
      ) {
        support = false;
      }
    }
    return shadow(this, "supportsFullscreen", support);
  },
  get supportsIntegratedFind() {