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.active) {
      return;
    }
    evt.preventDefault();
    const delta = normalizeWheelEventDelta(evt);
    const currentTime = new Date().getTime();
    const storedTime = this.mouseScrollTimeStamp;
    
    if (
      currentTime > storedTime &&
      currentTime - storedTime < MOUSE_SCROLL_COOLDOWN_TIME
    ) {
      return;
    }
    
    if (
      (this.mouseScrollDelta > 0 && delta < 0) ||
      (this.mouseScrollDelta < 0 && delta > 0)
    ) {
      this._resetMouseScrollState();
    }
    this.mouseScrollDelta += delta;
    if (Math.abs(this.mouseScrollDelta) >= PAGE_SWITCH_THRESHOLD) {
      const totalDelta = this.mouseScrollDelta;
      this._resetMouseScrollState();