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 (this.pdfDocument) {
      this.eventBus.dispatch("pagesdestroy", { source: this });
      this._cancelRendering();
      this._resetView();
      if (this.findController) {
        this.findController.setDocument(null);
      }
    }
    this.pdfDocument = pdfDocument;
    if (!pdfDocument) {
      return;
    }
    const pagesCount = pdfDocument.numPages;
    const firstPagePromise = pdfDocument.getPage(1);
    
    const optionalContentConfigPromise = pdfDocument.getOptionalContentConfig();
    this._pagesCapability.promise.then(() => {
      this.eventBus.dispatch("pagesloaded", {
        source: this,
        pagesCount,
      });