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._pageLabels) {
      return null;
    }
    const i = this._pageLabels.indexOf(label);
    if (i < 0) {
      return null;
    }
    return i + 1;
  }
  /**
   * @typedef ScrollPageIntoViewParameters
   * @property {number} pageNumber - The page number.
   * @property {Array} [destArray] - The original PDF destination array, in the
   *   format: <page-ref> </XYZ|/FitXXX> <args..>
   * @property {boolean} [allowNegativeOffset] - Allow negative page offsets.
   *   The default value is `false`.
   * @property {boolean} [ignoreDestinationZoom] - Ignore the zoom argument in
   *   the destination array. The default value is `false`.
   */
  /**
   * Scrolls page into view.
   * @param {ScrollPageIntoViewParameters} params
   */
  scrollPageIntoView({