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
let scale = parseFloat(value);
    if (scale > 0) {
      this._setScaleUpdatePages(scale, value, noScroll,  false);
    } else {
      const currentPage = this._pages[this._currentPageNumber - 1];
      if (!currentPage) {
        return;
      }
      const noPadding = this.isInPresentationMode || this.removePageBorders;
      let hPadding = noPadding ? 0 : SCROLLBAR_PADDING;
      let vPadding = noPadding ? 0 : VERTICAL_PADDING;
      if (!noPadding && this._isScrollModeHorizontal) {
        [hPadding, vPadding] = [vPadding, hPadding]; 
      }
      const pageWidthScale =
        (((this.container.clientWidth - hPadding) / currentPage.width) *
          currentPage.scale) /
        this._pageWidthScaleFactor;
      const pageHeightScale =
        ((this.container.clientHeight - vPadding) / currentPage.height) *
        currentPage.scale;
      switch (value) {
        case "page-actual":
          scale = 1;
          break;
        case "page-width":