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
const appConfig = this.appConfig;
    const eventBus =
      appConfig.eventBus ||
      new EventBus({ isInAutomation: this.externalServices.isInAutomation });
    this.eventBus = eventBus;
    this.overlayManager = new OverlayManager();
    const pdfRenderingQueue = new PDFRenderingQueue();
    pdfRenderingQueue.onIdle = this.cleanup.bind(this);
    this.pdfRenderingQueue = pdfRenderingQueue;
    const pdfLinkService = new PDFLinkService({
      eventBus,
      externalLinkTarget: AppOptions.get("externalLinkTarget"),
      externalLinkRel: AppOptions.get("externalLinkRel"),
      ignoreDestinationZoom: AppOptions.get("ignoreDestinationZoom"),
    });
    this.pdfLinkService = pdfLinkService;
    const downloadManager = this.externalServices.createDownloadManager();
    this.downloadManager = downloadManager;
    const findController = new PDFFindController({
      linkService: pdfLinkService,
      eventBus,
    });
    this.findController = findController;
    const container = appConfig.mainContainer;