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._currentScaleValue = newValue.toString();
    if (isSameScale(this._currentScale, newScale)) {
      if (preset) {
        this.eventBus.dispatch("scalechanging", {
          source: this,
          scale: newScale,
          presetValue: newValue,
        });
      }
      return;
    }
    for (let i = 0, ii = this._pages.length; i < ii; i++) {
      this._pages[i].update(newScale);
    }
    this._currentScale = newScale;
    if (!noScroll) {
      let page = this._currentPageNumber,
        dest;
      if (
        this._location &&
        !(this.isInPresentationMode || this.isChangingPresentationMode)
      ) {
        page = this._location.pageNumber;
        dest = [
          null,
          { name: "XYZ" },
          this._location.left,
          this._location.top,
          null,
        ];