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
this.viewer = options.viewer || options.container.firstElementChild;
    if (
      typeof PDFJSDev === "undefined" ||
      PDFJSDev.test("!PRODUCTION || GENERIC")
    ) {
      if (
        !(
          this.container?.tagName.toUpperCase() === "DIV" &&
          this.viewer?.tagName.toUpperCase() === "DIV"
        )
      ) {
        throw new Error("Invalid `container` and/or `viewer` option.");
      }
      if (getComputedStyle(this.container).position !== "absolute") {
        throw new Error("The `container` must be absolutely positioned.");
      }
    }
    this.eventBus = options.eventBus;
    this.linkService = options.linkService || new SimpleLinkService();
    this.downloadManager = options.downloadManager || null;
    this.findController = options.findController || null;
    this.removePageBorders = options.removePageBorders || false;
    this.textLayerMode = Number.isInteger(options.textLayerMode)
      ? options.textLayerMode
      : TextLayerMode.ENABLE;
    this.imageResourcesPath = options.imageResourcesPath || "";
    this.renderInteractiveForms =
      typeof options.renderInteractiveForms === "boolean"
        ? options.renderInteractiveForms
        : true;