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
if (!this.pagesCount) {
      return { views: [] };
    }
    const pageView = this._pages[this._currentPageNumber - 1];
    
    
    const element = pageView.div;
    const view = {
      id: pageView.id,
      x: element.offsetLeft + element.clientLeft,
      y: element.offsetTop + element.clientTop,
      view: pageView,
    };
    return { first: view, last: view, views: [view] };
  }
  _getVisiblePages() {
    return getVisibleElements({
      scrollEl: this.container,
      views: this._pages,
      sortByVisibility: true,
      horizontal: this._isScrollModeHorizontal,
      rtl: this._isScrollModeHorizontal && this._isContainerRtl,
    });
  }
  /**
   * @param {number} pageNumber
   */
  isPageVisible(pageNumber) {