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
*     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import { normalizeWheelEventDelta, PresentationModeState } from "./ui_utils.js";
const DELAY_BEFORE_RESETTING_SWITCH_IN_PROGRESS = 1500; 
const DELAY_BEFORE_HIDING_CONTROLS = 3000; 
const ACTIVE_SELECTOR = "pdfPresentationMode";
const CONTROLS_SELECTOR = "pdfPresentationModeControls";
const MOUSE_SCROLL_COOLDOWN_TIME = 50; 
const PAGE_SWITCH_THRESHOLD = 0.1;
const SWIPE_MIN_DISTANCE_THRESHOLD = 50;
const SWIPE_ANGLE_THRESHOLD = Math.PI / 6;
/**
 * @typedef {Object} PDFPresentationModeOptions
 * @property {HTMLDivElement} container - The container for the viewer element.
 * @property {PDFViewer} pdfViewer - The document viewer.
 * @property {EventBus} eventBus - The application event bus.
 * @property {Array} [contextMenuItems] - The menu items that are added to the
 *   context menu in Presentation Mode.
 */
class PDFPresentationMode {
  /**
   * @param {PDFPresentationModeOptions} options
   */
  constructor({ container, pdfViewer, eventBus, contextMenuItems = null }) {