It is not about your Firefox web browser but about your Mozilla Account as this support.mozilla.org site is one of the places you use a Mozilla Account for https://support.mozilla.org/en-US/kb/access-mozilla-services-firefox-account#w_what-services-can-i-use-with-a-mozilla-account Mozilla periodically deletes inactive accounts per their retention policies. If you haven’t signed in or used your account after two years, your account could be scheduled for deletion. You may want to check out [[Mozilla account deletion due to inactivity]]. That said, by using your Mozilla account to sign in and post a question here, your account should be safe.