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
pdfRenderingQueue.setThumbnailViewer(this.pdfThumbnailViewer);
    this.pdfHistory = new PDFHistory({
      linkService: pdfLinkService,
      eventBus,
    });
    pdfLinkService.setHistory(this.pdfHistory);
    if (!this.supportsIntegratedFind) {
      this.findBar = new PDFFindBar(appConfig.findBar, eventBus, this.l10n);
    }
    this.pdfDocumentProperties = new PDFDocumentProperties(
      appConfig.documentProperties,
      this.overlayManager,
      eventBus,
      this.l10n
    );
    this.pdfCursorTools = new PDFCursorTools({
      container,
      eventBus,
      cursorToolOnLoad: AppOptions.get("cursorToolOnLoad"),
    });
    this.toolbar = new Toolbar(appConfig.toolbar, eventBus, this.l10n);
    this.secondaryToolbar = new SecondaryToolbar(
      appConfig.secondaryToolbar,
      container,
      eventBus
    );
    if (this.supportsFullscreen) {
      this.pdfPresentationMode = new PDFPresentationMode({
        container,
        pdfViewer: this.pdfViewer,