[Bug]: Collapse all items on inital Document Outline

[a2zaustin]

Is the feature relevant to the Firefox PDF Viewer?

Yes

Feature description

Currently when the document outline is opened it is completely expanded so I manually close everything so my navigation can be cleaner. My suggested change would be, upon initial navigation to the document outline all items should be collapsed by default.

I have not labelled this as a bug, as I am not sure but I am on the following:

OS: Windows 11 Home
OS Version: 10.0.26200

Firefox Version: 146.0
Default PDF viewer

Other PDF viewers

No response

[a2zaustin]

Working Example:
rust-design-patterns.pdf

Failing Example:
CPlusPlusNotesForProfessionals.pdf

Since I was able to find a working example I am going to mark this as a bug instead.

[a2zaustin]

Steps to reproduce the problem:

1. Open in PDF viewer.
2. Navigate to document outline.

What is the expected behavior?

The outline should be collapsed completely.

What went wrong?

Everything is currently expanded by default.

[Riya-chandra]

Hi @timvandermeij,
I'd like to work on this issue, which also addresses the long-standing #7713.
After reviewing the codebase, I plan to modify the PDFOutlineViewer class in web/pdf_outline_viewer.js. Specifically, I'll locate the initialization logic that sets the default expansion behavior (likely in the constructor or _addToggleButton method) and change it to collapse all outline items initially. This will involve setting the appropriate CSS classes (treeItem elements should have the collapsed state by default) and ensuring the _setOpen method correctly handles the initial state. The existing toggle functionality through _bindLink will remain intact, allowing users to expand items on demand. I'll also check if there's a configuration parameter like this.maxExpandLevel or similar that controls the default expansion depth and set it to 0.
For testing, I'll verify the behavior with PDFs containing various outline structures (single-level, deeply nested, and no outline), run npx gulp unittest and npx gulp integrationtest, and test across different browsers to ensure consistency. If you have any specific implementation preferences or know the exact property/method I should modify, please let me know.
I'm ready to start immediately if you'd like to assign this to me. Thanks!