[Bug]: Combination of defaultZoomValue: page-height and scrollModeOnLoad: 3 = unable to scroll past page with keyboard

Attach (recommended) or Link to PDF file

Any multiple pages long PDF file will do.

Web browser and its version

Firefox 156.0 / Thunderbird 156.0 / Firefox 140.13.0esr

Operating system and its version

Windows 11 25H2

PDF.js version

(Sorry but: How can I find it?)

Is the bug present in the latest PDF.js version?

Yes

Is a browser extension

No

Steps to reproduce the problem

1. Set the following values in user.js:

• user_pref("pdfjs.defaultZoomValue", "page-height");
• user_pref("pdfjs.scrollModeOnLoad", 3); // 3 = page
• user_pref("pdfjs.viewOnLoad", 1); // Just to make sure the settings above are applied

2. Open any multiple site long PDF file
3. Try to scroll with the arrow or page up/down keys

What is the expected behavior?

The arrow or page up/down keys scroll to the next page of the PDF.

What went wrong?

PDF.js stays on the displayed page.

Link to a viewer

No response

Additional context

Using the up/down buttons in the toolbar, it is possible to scroll between pages.

When setting the zoom to any other setting and then resetting it to page-height, scrolling with those keyboard keys becomes possible.
So the issue only occurs when starting with the mentioned user.js settings.

Reproduce the issue in the PDF.js viewer using a multi-page PDF and the three user.js settings listed in the report. Start by tracing keyboard page navigation alongside the initial page-height zoom setup, then verify that arrow and page up/down keys advance pages without requiring a later zoom change.