1. Click Edit-> Mail & Newsgroup Account Settings
2. Click Add Account button
3. Choose Email Account. Click Next
4. Type name and email address in the boxes. Click Next
5. Choose POP and type 'localhost' as the incoming server.
6. Type '127.0.0.1' as the outgoing mail server.
7. Type your Yahoo user name. Click Next
8. Type the account name you want displayed in Mozilla Mail and click Next.
9. Verify the information and click Finish.

Enable authentication for outgoing mail. Provide your Yahoo email address as username and your Yahoo Mail password as the password.

The first time you try to access the account, Mozilla will ask for a password and if you want Mozilla to remember the password.