Bottom third of tall PDF document is clipped/unpainted

[dholbert]

Attach (recommended) or Link to PDF file here: u6-longrange.pdf

(original link: http://dl.ubnt.com/qig/u6-longrange , linked from https://store.ui.com/collections/unifi-network-access-points/products/unifi-6-long-range-access-point ("installation guide")

Configuration:

• Web browser and its version: Firefox Nightly 87.0a1 (2021-02-03) (64-bit)
• Operating system and its version: Ubuntu 20.10 and macOS 11.2 Big Sur (reproduced on both)
• PDF.js version: Whatever is currently shipping with Firefox Nightly (I don't recall how to tell)
• Is a browser extension: I'm using the built-in version that comes with Firefox.

Steps to reproduce the problem:

1. View the provided PDF (which is a single extremely-tall page; Ubiquiti seems to do this for their guides for some reason)
2. Try to scroll to the end.

What is the expected behavior?
You should see graphical content all the way to the end of the document.

What went wrong?
About 2/3 of the way through the document, the graphical content is abruptly clipped, and the rest of the document is just blank.

[calixteman]

I reproduce in firefox nightly on master (depends of the zoom level).
But I don't in chrome (using local server too).

[calixteman]

So it's ok with zoom at 121% (width=387px, height = 16335px) and it isn't at 122% (width = 390px, height = 16490px).
So I'd say that something is wrong when height is greater than 16384px but I don't find anything here:
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/canvas#maximum_canvas_size