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._wheelUnusedTicks > 0 && ticks < 0) ||
      (this._wheelUnusedTicks < 0 && ticks > 0)
    ) {
      this._wheelUnusedTicks = 0;
    }
    this._wheelUnusedTicks += ticks;
    const wholeTicks =
      Math.sign(this._wheelUnusedTicks) *
      Math.floor(Math.abs(this._wheelUnusedTicks));
    this._wheelUnusedTicks -= wholeTicks;
    return wholeTicks;
  },
  /**
   * Used together with the integration-tests, to enable awaiting full
   * initialization of the scripting/sandbox.
   */
  get scriptingReady() {