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
});
    it("gets PDF filename from (some) standard protocols", function () {
      
      expect(getPDFFileNameFromURL("http:www.example.com/file1.pdf")).toEqual(
        "file1.pdf"
      );
      
      expect(
        getPDFFileNameFromURL("https:www.example.com/file2.pdf")
      ).toEqual("file2.pdf");
      
      expect(getPDFFileNameFromURL("file:/path/to/files/file3.pdf")).toEqual(
        "file3.pdf"
      );
      
      expect(getPDFFileNameFromURL("ftp:www.example.com/file4.pdf")).toEqual(
        "file4.pdf"
      );
    });
    it('gets PDF filename from query string appended to "blob:" URL', function () {
      if (isNodeJS) {
        pending("Blob in not supported in Node.js.");
      }
      const typedArray = new Uint8Array([1, 2, 3, 4, 5]);
      const blobUrl = createObjectURL(typedArray, "application/pdf");
      
      expect(blobUrl.startsWith("blob:")).toEqual(true);
      expect(getPDFFileNameFromURL(blobUrl + "?file.pdf")).toEqual("file.pdf");
    });
    it('gets fallback filename from query string appended to "data:" URL', function () {