BB 44125: Do not offer to save signatures by default in Private Browsing Mode

        return this.#getSignatures(data);

      case "delete":

        return this.#deleteSignature(data);

      case "isVolatile":

        return lazy.PrivateBrowsingUtils.isBrowserPrivate(this.browser);

      default:

        return null;

    }

  async size() {

    return (await this.getAll()).size;

  }

  async isVolatile() {

    return await this.#handleSignature({action: "isVolatile"});

  }

  async create(data) {

    if (await this.isFull()) {

      return null;

    this.#uiManager.removeEditListeners();

    const isStorageFull = await this.#signatureStorage.isFull();

    this.#saveContainer.classList.toggle("fullStorage", isStorageFull);

    this.#saveCheckbox.checked = !isStorageFull;

    const isVolatile = await this.#signatureStorage.isVolatile();

    this.#saveCheckbox.checked = !(isStorageFull || isVolatile);

    await this.#overlayManager.open(this.#dialog);

    const tabType = this.#tabButtons.get("type");

    tabType.focus();