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
eventListeners.slice(0).forEach(({ listener, external, once }) => {
      if (once) {
        this._off(eventName, listener);
      }
      if (external) {
        (externalListeners ||= []).push(listener);
        return;
      }
      listener.apply(null, args);
    });
    
    
    if (externalListeners) {
      externalListeners.forEach(listener => {
        listener.apply(null, args);
      });
      externalListeners = null;
    }
    if (
      (typeof PDFJSDev === "undefined" || PDFJSDev.test("MOZCENTRAL")) &&
      this._isInAutomation
    ) {
      dispatchDOMEvent(eventName, args);
    }
  }
  /**
   * @ignore
   */
  _on(eventName, listener, options = null) {