Add check update feature for Firefox Scripts

[Merci-chao]

Since the script loader typically requires updates only when it fails, I propose adding a check-for-update feature to improve reliability.

For example, I have implemented logic in my scripts that compares the local version information with the remote file available in the repository: https://github.com/Merci-chao/userChrome.js/blob/fc941b9235939c6b08d1719e48c2fb41804d40f3/PageTitle%40Merci.chao.uc.js#L43-L90