Attach (recommended) or Link to PDF file here:
See pdf in https://github.com/mozilla/pdf.js/issues/3109

Configuration:
- Web browser and its version: Firefox nightly
- Operating system and its version: Windows 10
- PDF.js version: builtin viewer

Steps to reproduce the problem:
1. Look at outlines

What is the expected behavior? (add screenshot)
![image](https://user-images.githubusercontent.com/5641725/141514798-0e656865-1cbf-4fb8-a89b-530d36da23c9.png)

What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/5641725/141514740-c95e0237-8bf4-4129-a4a5-cb2ea5a3f4df.png)

const toggler = document.createElement("div");
    toggler.className = "treeItemToggler";
    if (hidden) {
      toggler.classList.add("treeItemsHidden");
    }
    toggler.onclick = evt => {
      evt.stopPropagation();
      toggler.classList.toggle("treeItemsHidden");
      if (evt.shiftKey) {
        const shouldShowAll = !toggler.classList.contains("treeItemsHidden");
        this._toggleTreeItem(div, shouldShowAll);
      }
    };
    div.insertBefore(toggler, div.firstChild);
  }
  /**
   * Collapse or expand the subtree of a tree item.
   *
   * @param {Element} root - the root of the item (sub)tree.
   * @param {boolean} show - whether to show the item (sub)tree. If false,
   *   the item subtree rooted at `root` will be collapsed.
   * @private
   */
  _toggleTreeItem(root, show = false) {