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.documentInfo = info;
    this.metadata = metadata;
    this._contentDispositionFilename = contentDispositionFilename;
    this._contentLength ??= contentLength; 
    
    console.log(
      `PDF ${pdfDocument.fingerprint} [${info.PDFFormatVersion} ` +
        `${(info.Producer || "-").trim()} / ${(info.Creator || "-").trim()}] ` +
        `(PDF.js: ${version || "-"}` +
        `${this.pdfViewer.enableWebGL ? " [WebGL]" : ""})`
    );
    let pdfTitle;
    const infoTitle = info && info.Title;
    if (infoTitle) {
      pdfTitle = infoTitle;
    }
    const metadataTitle = metadata && metadata.get("dc:title");
    if (metadataTitle) {
      
      
      
      
      
      
      if (
        metadataTitle !== "Untitled" &&
        !/[\uFFF0-\uFFFF]/g.test(metadataTitle)
      ) {
        pdfTitle = metadataTitle;