Do you mean that you want to set up "Two-step" authentication on your account? That isn't needed to use the account, but provides some protection against third party access. It also increases the risk of losing access to your own account in the future. One of the methods doesn't require a mobile phone, according to this article: [[Secure your Firefox Account with two-step authentication]]. It is a desktop app for Windows or Mac. However, I have never tried it myself.