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
WaitOnType,
} from "../../web/ui_utils.js";
import { createObjectURL } from "../../src/shared/util.js";
import { isNodeJS } from "../../src/shared/is_node.js";
describe("ui_utils", function () {
  describe("binary search", function () {
    function isTrue(boolean) {
      return boolean;
    }
    function isGreater3(number) {
      return number > 3;
    }
    it("empty array", function () {
      expect(binarySearchFirstItem([], isTrue)).toEqual(0);
    });
    it("single boolean entry", function () {
      expect(binarySearchFirstItem([false], isTrue)).toEqual(1);
      expect(binarySearchFirstItem([true], isTrue)).toEqual(0);
    });
    it("three boolean entries", function () {
      expect(binarySearchFirstItem([true, true, true], isTrue)).toEqual(0);
      expect(binarySearchFirstItem([false, true, true], isTrue)).toEqual(1);
      expect(binarySearchFirstItem([false, false, true], isTrue)).toEqual(2);
      expect(binarySearchFirstItem([false, false, false], isTrue)).toEqual(3);
    });
    it("three numeric entries", function () {
      expect(binarySearchFirstItem([0, 1, 2], isGreater3)).toEqual(3);
      expect(binarySearchFirstItem([2, 3, 4], isGreater3)).toEqual(2);
      expect(binarySearchFirstItem([4, 5, 6], isGreater3)).toEqual(0);
    });