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 (!isValidRotation(rotation)) {
      throw new Error("Invalid pages rotation angle.");
    }
    if (!this.pdfDocument) {
      return;
    }
    if (this._pagesRotation === rotation) {
      return; 
    }
    this._pagesRotation = rotation;
    const pageNumber = this._currentPageNumber;
    for (let i = 0, ii = this._pages.length; i < ii; i++) {
      const pageView = this._pages[i];
      pageView.update(pageView.scale, rotation);
    }
    
    
    if (this._currentScaleValue) {
      this._setScale(this._currentScaleValue, true);
    }
    this.eventBus.dispatch("rotationchanging", {
      source: this,
      pagesRotation: rotation,
      pageNumber,
    });
    if (this.defaultRenderingQueue) {
      this.update();
    }
  }
  get firstPagePromise() {