More than one page is displayed in the presentation mode

[radarfox]

Attach (recommended) or Link to PDF file here:

example-horizontal.pdf

Configuration:

• Web browser and its version: Firefox 67, Chrome 75
• Operating system and its version: Windows 10
• PDF.js version: 2.1.266
• Is a browser extension: no

Steps to reproduce the problem:

1. Open a PDF with horizontal pages on the portrait orientated display.
2. You can see one, two or even more pages at the same time, depends on the dimensions of the pages and the display.
3. The problem is caused by the page separation which is done just by the simple margin-bottom: 100%; assigned to the .page elements. But the 100% is computed from the PDF page width, not from the height of the display. So when the sum of the PDF page width and height is greater than the height of the display, this error occurs.

What is the expected behavior? (add screenshot)

To display only one PDF page in the presentation mode.

What went wrong? (add screenshot)

Note the next page header displayed on the bottom of the following screenshot.

[radarfox]

This problem might be related to #10906. If the vertical centering is done correctly, this problem would disappear.