<blockquote> I need to attach a Thunderbird or Yahoo Email Address to my Firefox account </blockquote> I don't understand what that means. What are you trying to achieve in the first place? Beyond that, there is no such thing as a "Thunderbird account" or "Thunderbird Email Address". Neither Thunderbird nor Mozilla are an email provider. You've set up an account with an email provider, e.g. Gmail or Yahoo. Then you use Thunderbird to access mail for that account on your email provider's server, as well as to send mail via your email provider's server.