Mozilla who makes the Firefox web browsers for Windows, macOS, Linux and mobile versions for Android and iOS/iPadOS does not have a email service for the general public. They do manually provide *@mozilla.org email addresses to people who work for Mozilla in a capacity that warrants getting one. They have to give it up when they leave. If you mean Mozilla Account formerly known as Firefox Account til Nov 2023 then you already have at least one as you are using a Mozilla Account to post this thread on this community support forum. https://support.mozilla.org/en-US/kb/access-mozilla-services-firefox-account