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.enablePrintAutoRotate = options.enablePrintAutoRotate || false;
    this.renderer = options.renderer || RendererType.CANVAS;
    this.enableWebGL = options.enableWebGL || false;
    this.useOnlyCssZoom = options.useOnlyCssZoom || false;
    this.maxCanvasPixels = options.maxCanvasPixels;
    this.l10n = options.l10n || NullL10n;
    this.enableScripting = options.enableScripting || false;
    this._mouseState = options.mouseState || null;
    this.defaultRenderingQueue = !options.renderingQueue;
    if (this.defaultRenderingQueue) {
      
      this.renderingQueue = new PDFRenderingQueue();
      this.renderingQueue.setViewer(this);
    } else {
      this.renderingQueue = options.renderingQueue;
    }
    this.scroll = watchScroll(this.container, this._scrollUpdate.bind(this));
    this.presentationModeState = PresentationModeState.UNKNOWN;
    this._onBeforeDraw = this._onAfterDraw = null;
    this._resetView();
    if (this.removePageBorders) {
      this.viewer.classList.add("removePageBorders");
    }
    
    
    Promise.resolve().then(() => {
      this.eventBus.dispatch("baseviewerinit", { source: this });
    });
  }
  get pagesCount() {