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)

constructor(options) {
    if (this.constructor === BaseTreeViewer) {
      throw new Error("Cannot initialize BaseTreeViewer.");
    }
    this.container = options.container;
    this.eventBus = options.eventBus;
    this.reset();
  }
  reset() {
    this._pdfDocument = null;
    this._lastToggleIsShow = true;
    this._currentTreeItem = null;
    
    this.container.textContent = "";
    
    
    this.container.classList.remove("treeWithDeepNesting");
  }
  /**
   * @private
   */
  _dispatchEvent(count) {