Register for a Mozilla Persona user account
In order to be able to install an app, you’ll need to sign in to Firefox Marketplace with your Mozilla Persona user account. If you don’t have an account, just register a new account. (A Mozilla Persona account also enables you to sync your Firefox browser’s bookmarks and settings across your computers and devices that have Firefox installed on them.) All the apps in Firefox Marketplace are free to install, but Mozilla plans to allow developers to sell their apps.