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
});
      
      pageRendered.then(function (type) {
        expect(type).toEqual(WaitOnType.TIMEOUT);
        done();
      }, done.fail);
    });
  });
  describe("getPageSizeInches", function () {
    it("gets page size (in inches)", function () {
      const page = {
        view: [0, 0, 595.28, 841.89],
        userUnit: 1.0,
        rotate: 0,
      };
      const { width, height } = getPageSizeInches(page);
      expect(+width.toPrecision(3)).toEqual(8.27);
      expect(+height.toPrecision(4)).toEqual(11.69);
    });
    it("gets page size (in inches), for non-default /Rotate entry", function () {
      const pdfPage1 = { view: [0, 0, 612, 792], userUnit: 1, rotate: 0 };
      const { width: width1, height: height1 } = getPageSizeInches(pdfPage1);
      expect(width1).toEqual(8.5);
      expect(height1).toEqual(11);
      const pdfPage2 = { view: [0, 0, 612, 792], userUnit: 1, rotate: 90 };
      const { width: width2, height: height2 } = getPageSizeInches(pdfPage2);
      expect(width2).toEqual(11);
      expect(height2).toEqual(8.5);
    });
  });