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
const previousScale = pdfViewer.currentScale;
    const delta = normalizeWheelEventDirection(evt);
    let ticks = 0;
    if (
      evt.deltaMode === WheelEvent.DOM_DELTA_LINE ||
      evt.deltaMode === WheelEvent.DOM_DELTA_PAGE
    ) {
      
      
      
      
      if (Math.abs(delta) >= 1) {
        ticks = Math.sign(delta);
      } else {
        
        
        ticks = PDFViewerApplication.accumulateWheelTicks(delta);
      }
    } else {
      
      const PIXELS_PER_LINE_SCALE = 30;
      ticks = PDFViewerApplication.accumulateWheelTicks(
        delta / PIXELS_PER_LINE_SCALE
      );
    }
    if (ticks < 0) {
      PDFViewerApplication.zoomOut(-ticks);
    } else if (ticks > 0) {
      PDFViewerApplication.zoomIn(ticks);
    }