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 (!PDFViewerApplication.supportsFullscreen) {
    appConfig.toolbar.presentationModeButton.classList.add("hidden");
    appConfig.secondaryToolbar.presentationModeButton.classList.add("hidden");
  }
  if (PDFViewerApplication.supportsIntegratedFind) {
    appConfig.toolbar.viewFind.classList.add("hidden");
  }
  appConfig.mainContainer.addEventListener(
    "transitionend",
    function (evt) {
      if (evt.target ===  this) {
        PDFViewerApplication.eventBus.dispatch("resize", { source: this });
      }
    },
    true
  );
  try {
    webViewerOpenFileViaURL(file);
  } catch (reason) {
    PDFViewerApplication.l10n
      .get("loading_error", null, "An error occurred while loading the PDF.")
      .then(msg => {
        PDFViewerApplication.error(msg, reason);
      });
  }
}
let webViewerOpenFileViaURL;
if (typeof PDFJSDev === "undefined" || PDFJSDev.test("GENERIC")) {
  webViewerOpenFileViaURL = function (file) {
    if (file && file.lastIndexOf("file:", 0) === 0) {