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.linkService.cachePageRef(pageNum, pdfPage.ref);
                if (--getPagesLeft === 0) {
                  this._pagesCapability.resolve();
                }
              },
              reason => {
                console.error(
                  `Unable to get page ${pageNum} to initialize viewer`,
                  reason
                );
                if (--getPagesLeft === 0) {
                  this._pagesCapability.resolve();
                }
              }
            );
          }
        });
        this.eventBus.dispatch("pagesinit", { source: this });
        if (this.defaultRenderingQueue) {
          this.update();
        }
      })
      .catch(reason => {
        console.error("Unable to initialize viewer", reason);
      });
  }
  /**
   * @param {Array|null} labels
   */
  setPageLabels(labels) {