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
parameters[key] = args[key];
      }
    }
    const loadingTask = getDocument(parameters);
    this.pdfLoadingTask = loadingTask;
    loadingTask.onPassword = (updateCallback, reason) => {
      this.pdfLinkService.externalLinkEnabled = false;
      this.passwordPrompt.setUpdateCallback(updateCallback, reason);
      this.passwordPrompt.open();
    };
    loadingTask.onProgress = ({ loaded, total }) => {
      this.progress(loaded / total);
    };
    
    loadingTask.onUnsupportedFeature = this.fallback.bind(this);
    return loadingTask.promise.then(
      pdfDocument => {
        this.load(pdfDocument);
      },
      exception => {
        if (loadingTask !== this.pdfLoadingTask) {
          return undefined; 
        }
        const message = exception?.message;
        let loadingErrorMessage;
        if (exception instanceof InvalidPDFException) {
          
          loadingErrorMessage = this.l10n.get(
            "invalid_file_error",
            null,