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.pdfDocument = pdfDocument;
    pdfDocument.getDownloadInfo().then(({ length }) => {
      this._contentLength = length; 
      this.downloadComplete = true;
      this.loadingBar.hide();
      firstPagePromise.then(() => {
        this.eventBus.dispatch("documentloaded", { source: this });
      });
    });
    
    
    const pageLayoutPromise = pdfDocument.getPageLayout().catch(function () {
      
    });
    const pageModePromise = pdfDocument.getPageMode().catch(function () {
      
    });
    const openActionPromise = pdfDocument.getOpenAction().catch(function () {
      
    });
    this.toolbar.setPagesCount(pdfDocument.numPages, false);
    this.secondaryToolbar.setPagesCount(pdfDocument.numPages);
    let baseDocumentUrl;
    if (typeof PDFJSDev === "undefined" || PDFJSDev.test("GENERIC")) {
      baseDocumentUrl = null;
    } else if (PDFJSDev.test("MOZCENTRAL")) {
      baseDocumentUrl = this.baseUrl;