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
* @property {PDFFindController} [findController] - The find controller
 *   component.
 * @property {PDFRenderingQueue} [renderingQueue] - The rendering queue object.
 * @property {boolean} [removePageBorders] - Removes the border shadow around
 *   the pages. The default value is `false`.
 * @property {number} [textLayerMode] - Controls if the text layer used for
 *   selection and searching is created, and if the improved text selection
 *   behaviour is enabled. The constants from {TextLayerMode} should be used.
 *   The default value is `TextLayerMode.ENABLE`.
 * @property {string} [imageResourcesPath] - Path for image resources, mainly
 *   mainly for annotation icons. Include trailing slash.
 * @property {boolean} [renderInteractiveForms] - Enables rendering of
 *   interactive form elements. The default value is `true`.
 * @property {boolean} [enablePrintAutoRotate] - Enables automatic rotation of
 *   landscape pages upon printing. The default is `false`.
 * @property {string} renderer - 'canvas' or 'svg'. The default is 'canvas'.
 * @property {boolean} [enableWebGL] - Enables WebGL accelerated rendering for
 *   some operations. The default value is `false`.
 * @property {boolean} [useOnlyCssZoom] - Enables CSS only zooming. The default
 *   value is `false`.
 * @property {number} [maxCanvasPixels] - The maximum supported canvas size in
 *   total pixels, i.e. width * height. Use -1 for no limit. The default value
 *   is 4096 * 4096 (16 mega-pixels).
 * @property {IL10n} l10n - Localization service.
 * @property {boolean} [enableScripting] - Enable embedded script execution.
 *   The default value is `false`.
 * @property {Object} [mouseState] - The mouse button state. The default value
 *   is `null`.
 */
function PDFPageViewBuffer(size) {