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
Number.isInteger(pageNumber) && this._pages[pageNumber - 1];
    if (!pageView) {
      console.error(
        `${this._name}.scrollPageIntoView: ` +
          `"${pageNumber}" is not a valid pageNumber parameter.`
      );
      return;
    }
    if (this.isInPresentationMode || !destArray) {
      this._setCurrentPageNumber(pageNumber,  true);
      return;
    }
    let x = 0,
      y = 0;
    let width = 0,
      height = 0,
      widthScale,
      heightScale;
    const changeOrientation = pageView.rotation % 180 !== 0;
    const pageWidth =
      (changeOrientation ? pageView.height : pageView.width) /
      pageView.scale /
      CSS_UNITS;
    const pageHeight =
      (changeOrientation ? pageView.width : pageView.height) /
      pageView.scale /
      CSS_UNITS;
    let scale = 0;
    switch (destArray[1].name) {
      case "XYZ":