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
{ file: moreInfo.filename },
              "File: {{file}}"
            )
          );
        }
        if (moreInfo.lineNumber) {
          moreInfoText.push(
            this.l10n.get(
              "error_line",
              { line: moreInfo.lineNumber },
              "Line: {{line}}"
            )
          );
        }
      }
    }
    if (typeof PDFJSDev === "undefined" || !PDFJSDev.test("MOZCENTRAL")) {
      const errorWrapperConfig = this.appConfig.errorWrapper;
      const errorWrapper = errorWrapperConfig.container;
      errorWrapper.removeAttribute("hidden");
      const errorMessage = errorWrapperConfig.errorMessage;
      errorMessage.textContent = message;
      const closeButton = errorWrapperConfig.closeButton;
      closeButton.onclick = function () {
        errorWrapper.setAttribute("hidden", "true");
      };
      const errorMoreInfo = errorWrapperConfig.errorMoreInfo;
      const moreInfoButton = errorWrapperConfig.moreInfoButton;
      const lessInfoButton = errorWrapperConfig.lessInfoButton;
      moreInfoButton.onclick = function () {