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
return destLength === 2;
    case "FitH":
    case "FitBH":
    case "FitV":
    case "FitBV":
      if (destLength !== 3) {
        return false;
      }
      break;
    case "FitR":
      if (destLength !== 6) {
        return false;
      }
      allowNull = false;
      break;
    default:
      return false;
  }
  for (let i = 2; i < destLength; i++) {
    const param = dest[i];
    if (!(typeof param === "number" || (allowNull && param === null))) {
      return false;
    }
  }
  return true;
}
/**
 * @implements {IPDFLinkService}
 */
class SimpleLinkService {