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
errorMoreInfo.removeAttribute("hidden");
        moreInfoButton.setAttribute("hidden", "true");
        lessInfoButton.removeAttribute("hidden");
        errorMoreInfo.style.height = errorMoreInfo.scrollHeight + "px";
      };
      lessInfoButton.onclick = function () {
        errorMoreInfo.setAttribute("hidden", "true");
        moreInfoButton.removeAttribute("hidden");
        lessInfoButton.setAttribute("hidden", "true");
      };
      moreInfoButton.oncontextmenu = noContextMenuHandler;
      lessInfoButton.oncontextmenu = noContextMenuHandler;
      closeButton.oncontextmenu = noContextMenuHandler;
      moreInfoButton.removeAttribute("hidden");
      lessInfoButton.setAttribute("hidden", "true");
      Promise.all(moreInfoText).then(parts => {
        errorMoreInfo.value = parts.join("\n");
      });
    } else {
      Promise.all(moreInfoText).then(parts => {
        console.error(message + "\n" + parts.join("\n"));
      });
      this.fallback();
    }
  },
  progress(level) {
    if (this.downloadComplete) {
      
      
      return;