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
}
    if ("disablestream" in hashParams) {
      AppOptions.set("disableStream", hashParams.disablestream === "true");
    }
    if ("disableautofetch" in hashParams) {
      AppOptions.set(
        "disableAutoFetch",
        hashParams.disableautofetch === "true"
      );
    }
    if ("disablefontface" in hashParams) {
      AppOptions.set("disableFontFace", hashParams.disablefontface === "true");
    }
    if ("disablehistory" in hashParams) {
      AppOptions.set("disableHistory", hashParams.disablehistory === "true");
    }
    if ("webgl" in hashParams) {
      AppOptions.set("enableWebGL", hashParams.webgl === "true");
    }
    if ("verbosity" in hashParams) {
      AppOptions.set("verbosity", hashParams.verbosity | 0);
    }
    if ("textlayer" in hashParams) {
      switch (hashParams.textlayer) {
        case "off":
          AppOptions.set("textLayerMode", TextLayerMode.DISABLE);
          break;
        case "visible":
        case "shadow":
        case "hover":