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
const eventListeners = (this._listeners[eventName] ||= []);
    eventListeners.push({
      listener,
      external: options?.external === true,
      once: options?.once === true,
    });
  }
  /**
   * @ignore
   */
  _off(eventName, listener, options = null) {
    const eventListeners = this._listeners[eventName];
    if (!eventListeners) {
      return;
    }
    for (let i = 0, ii = eventListeners.length; i < ii; i++) {
      if (eventListeners[i].listener === listener) {
        eventListeners.splice(i, 1);
        return;
      }
    }
  }
}
function clamp(v, min, max) {
  return Math.min(Math.max(v, min), max);
}
class ProgressBar {