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 (pageView.pdfPage) {
      return Promise.resolve(pageView.pdfPage);
    }
    if (this._pagesRequests.has(pageView)) {
      return this._pagesRequests.get(pageView);
    }
    const promise = this.pdfDocument
      .getPage(pageView.id)
      .then(pdfPage => {
        if (!pageView.pdfPage) {
          pageView.setPdfPage(pdfPage);
        }
        this._pagesRequests.delete(pageView);
        return pdfPage;
      })
      .catch(reason => {
        console.error("Unable to get page for page view", reason);
        
        this._pagesRequests.delete(pageView);
      });
    this._pagesRequests.set(pageView, promise);
    return promise;
  }
  forceRendering(currentlyVisiblePages) {