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
PDFViewerApplication.zoomIn();
}
function webViewerZoomOut() {
  PDFViewerApplication.zoomOut();
}
function webViewerZoomReset() {
  PDFViewerApplication.zoomReset();
}
function webViewerPageNumberChanged(evt) {
  const pdfViewer = PDFViewerApplication.pdfViewer;
  
  
  if (evt.value !== "") {
    PDFViewerApplication.pdfLinkService.goToPage(evt.value);
  }
  
  
  if (
    evt.value !== pdfViewer.currentPageNumber.toString() &&
    evt.value !== pdfViewer.currentPageLabel
  ) {
    PDFViewerApplication.toolbar.setPageNumber(
      pdfViewer.currentPageNumber,
      pdfViewer.currentPageLabel
    );
  }
}
function webViewerScaleChanged(evt) {