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
const SpreadMode = {
  UNKNOWN: -1,
  NONE: 0, 
  ODD: 1,
  EVEN: 2,
};
const AutoPrintRegExp = /\bprint\s*\(/;
function formatL10nValue(text, args) {
  if (!args) {
    return text;
  }
  return text.replace(/\{\{\s*(\w+)\s*\}\}/g, (all, name) => {
    return name in args ? args[name] : "{{" + name + "}}";
  });
}
/**
 * No-op implementation of the localization service.
 * @implements {IL10n}
 */
const NullL10n = {
  async getLanguage() {
    return "en-us";
  },
  async getDirection() {
    return "ltr";
  },
  async get(property, args, fallback) {
    return formatL10nValue(fallback, args);
  },
  async translate(element) {},