STR:
  - Go to https://mozilla.github.io/pdf.js/web/viewer.html
  - Click on "Open File" and open a pdf

The `Download` button and the `Current view` one just disappear.
I can reproduce this bug with Firefox nightly, Chrome stable and Epiphany on debian.
this.preferences = this.externalServices.createPreferences();
    this.appConfig = appConfig;
    await this._readPreferences();
    await this._parseHashParameters();
    this._forceCssTheme();
    await this._initializeL10n();
    if (
      this.isViewerEmbedded &&
      AppOptions.get("externalLinkTarget") === LinkTarget.NONE
    ) {
      
      
      AppOptions.set("externalLinkTarget", LinkTarget.TOP);
    }
    await this._initializeViewerComponents();
    
    
    this.bindEvents();
    this.bindWindowEvents();
    
    const appContainer = appConfig.appContainer || document.documentElement;
    this.l10n.translate(appContainer).then(() => {