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
null,
          "Warning: The PDF is not fully loaded for printing."
        )
        .then(notReadyMessage => {
          
          window.alert(notReadyMessage);
        });
      return;
    }
    const pagesOverview = this.pdfViewer.getPagesOverview();
    const printContainer = this.appConfig.printContainer;
    const printResolution = AppOptions.get("printResolution");
    const optionalContentConfigPromise = this.pdfViewer
      .optionalContentConfigPromise;
    const printService = PDFPrintServiceFactory.instance.createPrintService(
      this.pdfDocument,
      pagesOverview,
      printContainer,
      printResolution,
      optionalContentConfigPromise,
      this.l10n
    );
    this.printService = printService;
    this.forceRendering();
    printService.layout();
    this.externalServices.reportTelemetry({
      type: "print",
    });
  },
  afterPrint() {