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
*   relevant layout assumptions.
 * @property {boolean} sortByVisibility - If `true`, the returned elements are
 *   sorted in descending order of the percent of their padding box that is
 *   visible. The default value is `false`.
 * @property {boolean} horizontal - If `true`, the elements are assumed to be
 *   laid out horizontally instead of vertically. The default value is `false`.
 * @property {boolean} rtl - If `true`, the `scrollEl` container is assumed to
 *   be in right-to-left mode. The default value is `false`.
 */
/**
 * Generic helper to find out what elements are visible within a scroll pane.
 *
 * Well, pretty generic. There are some assumptions placed on the elements
 * referenced by `views`:
 *   - If `horizontal`, no left of any earlier element is to the right of the
 *     left of any later element.
 *   - Otherwise, `views` can be split into contiguous rows where, within a row,
 *     no top of any element is below the bottom of any other element, and
 *     between rows, no bottom of any element in an earlier row is below the
 *     top of any element in a later row.
 *
 * (Here, top, left, etc. all refer to the padding edge of the element in
 * question. For pages, that ends up being equivalent to the bounding box of the
 * rendering canvas. Earlier and later refer to index in `views`, not page
 * layout.)
 *
 * @param {GetVisibleElementsParameters}
 * @returns {Object} `{ first, last, views: [{ id, x, y, view, percent }] }`
 */
function getVisibleElements({