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
dest = [
            null,
            { name: "XYZ" },
            zoomArgs.length > 1 ? zoomArgs[1] | 0 : null,
            zoomArgs.length > 2 ? zoomArgs[2] | 0 : null,
            zoomArgNumber ? zoomArgNumber / 100 : zoomArg,
          ];
        } else {
          if (zoomArg === "Fit" || zoomArg === "FitB") {
            dest = [null, { name: zoomArg }];
          } else if (
            zoomArg === "FitH" ||
            zoomArg === "FitBH" ||
            zoomArg === "FitV" ||
            zoomArg === "FitBV"
          ) {
            dest = [
              null,
              { name: zoomArg },
              zoomArgs.length > 1 ? zoomArgs[1] | 0 : null,
            ];
          } else if (zoomArg === "FitR") {
            if (zoomArgs.length !== 5) {
              console.error(
                'PDFLinkService.setHash: Not enough parameters for "FitR".'
              );
            } else {
              dest = [
                null,