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
return; 
      }
      await this._scriptingInstance?.scripting.dispatchEventInSandbox({
        id: "page",
        name: "PageClose",
        pageNumber,
      });
    };
    internalEvents.set("pageopen", pageOpen);
    internalEvents.set("pageclose", pageClose);
    const dispatchEventInSandbox = ({ detail }) => {
      scripting.dispatchEventInSandbox(detail);
    };
    internalEvents.set("dispatcheventinsandbox", dispatchEventInSandbox);
    const mouseDown = event => {
      this._mouseState.isDown = true;
    };
    domEvents.set("mousedown", mouseDown);
    const mouseUp = event => {
      this._mouseState.isDown = false;
    };
    domEvents.set("mouseup", mouseUp);
    for (const [name, listener] of internalEvents) {
      this.eventBus._on(name, listener);
    }
    for (const [name, listener] of domEvents) {
      window.addEventListener(name, listener);
    }
    try {
      await scripting.createSandbox({