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.pdfViewer.currentPageNumber = value + 1;
            break;
          case "print":
            this.pdfViewer.pagesPromise.then(() => {
              this.triggerPrinting();
            });
            break;
          case "println":
            console.log(value);
            break;
          case "zoom":
            this.pdfViewer.currentScaleValue = value;
            break;
        }
        return;
      }
      const element = document.getElementById(id);
      if (element) {
        element.dispatchEvent(new CustomEvent("updatefromsandbox", { detail }));
      } else {
        if (value !== undefined && value !== null) {
          
          pdfDocument.annotationStorage.setValue(id, value);
        }
      }
    };
    internalEvents.set("updatefromsandbox", updateFromSandbox);
    const visitedPages = new Map();
    const pageOpen = ({ pageNumber, actionsPromise }) => {
      visitedPages.set(