Livestore fails to load in private browsing on Firefox

Repro (per title):

1. Open firefox in private browsing mode (aka incognito)
2. Attempt to run livestore

Actual error:

Uncaught (in promise) DOMException: Security error when calling GetDirectory opfs-utils.ts:18

It looks like getDirectory is not allowed, and needs to be handled. Relevant MDN docs: https://developer.mozilla.org/en-US/docs/Web/API/StorageManager/getDirectory

SecurityError DOMException Thrown if the browser is not able to map the requested directory to the local OPFS, for example due to storage or memory > constraints. Also thrown in some browsers if getDirectory() is called in private browsing mode.

Relevant livestore snippet

// To improve LiveStore compatibility with e.g. Node.js we're guarding for `navigator` / `navigator.storage` to be defined.
export const rootHandlePromise =
  typeof navigator === 'undefined' || navigator.storage === undefined
    ? // We're using a proxy here to make the promise reject lazy
      (new Proxy(
        {},
        {
          get: () =>
            Promise.reject(
              new Error(`Can't get OPFS root handle in this environment as navigator.storage is undefined`),
            ),
        },
      ) as never)
    : navigator.storage.getDirectory()