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.toolbar.setPageNumber(
      this.pdfViewer.currentPageNumber,
      this.pdfViewer.currentPageLabel
    );
    this.secondaryToolbar.setPageNumber(this.pdfViewer.currentPageNumber);
    if (!this.pdfViewer.currentScaleValue) {
      
      
      this.pdfViewer.currentScaleValue = DEFAULT_SCALE_VALUE;
    }
  },
  cleanup() {
    if (!this.pdfDocument) {
      return; 
    }
    this.pdfViewer.cleanup();
    this.pdfThumbnailViewer.cleanup();
    
    if (this.pdfViewer.renderer !== RendererType.SVG) {
      this.pdfDocument.cleanup();
    }
  },
  forceRendering() {
    this.pdfRenderingQueue.printing = !!this.printService;
    this.pdfRenderingQueue.isThumbnailViewEnabled = this.pdfSidebar.isThumbnailViewVisible;
    this.pdfRenderingQueue.renderHighestPriority();
  },
  beforePrint() {