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._spreadMode !== SpreadMode.NONE) {
          this._updateSpreadMode();
        }
        
        
        
        this._onePageRenderedOrForceFetch().then(() => {
          if (this.findController) {
            this.findController.setDocument(pdfDocument); 
          }
          
          
          if (pdfDocument.loadingParams.disableAutoFetch || pagesCount > 7500) {
            
            this._pagesCapability.resolve();
            return;
          }
          let getPagesLeft = pagesCount - 1; 
          if (getPagesLeft <= 0) {
            this._pagesCapability.resolve();
            return;
          }
          for (let pageNum = 2; pageNum <= pagesCount; ++pageNum) {
            pdfDocument.getPage(pageNum).then(
              pdfPage => {
                const pageView = this._pages[pageNum - 1];
                if (!pageView.pdfPage) {
                  pageView.setPdfPage(pdfPage);
                }