Page turning while PDF is loading

I am using the PineNote, an E-Ink Linux tablet, to play with my band. It is running Charts in the browser, and is understandably slow on that limited hardware. Especially PDFs are a pain point as they load so slowly that I can watch the individual elements making up the page appear one by one, and I cannot just let it load everything before service because only the few next pages are being kept in memory as it seems. But that is manageable, problematic is only the following:

Expectation: Using the arrow keys or buttons should navigate to the previous/next page immediately, letting the ongoing PDF load continue in the background, pause until the page is focused again, or aborted entirely.
Actual observation: Using the arrow keys or buttons does not turn the page. The header does change as if the page was turned, but the page stays the same even after PDF loading and rendering finishes. Navigating using the song list in the burger menu seems to work more reliably.

I was able to reproduce this on my old laptop in Chromium using 20× CPU slowdown (Dev tools → Performance tab → Environment settings (on the right side) → set dropdown to CPU: 20× slowdown) – for reference, my browser calibrated to need 5.2× slowdown for the Low-tier mobile device emulation and 1.4× slowdown for the Mid tier device emulation. Using 20× CPU slowdown the PDF loading effect was visible, but still more then twice as fast as on my PineNote – though in any way sufficient to reproduce the bug with page turning.

Hardware:
PineNote (from October 2024 batch) https://pine64.org/documentation/PineNote/Further_information/Specification/
CPU: RK3566 1.8GHz 64-bit quad-core A55
GPU: MALI G52 2EE

System:
Debian GNU/Linux trixie/sid
Linux pinenote 6.12.11-pinenote-202502161807-00386-gc94452303a55 #1 SMP Sun Feb 16 18:25:22 CST 2025 aarch64 GNU/Linux

Browser:
Firefox ESR 128.8.0esr (64-bit)