When opening my Yahoo mail client, although it does show the address header, there is no text. This is true of all my Yahoo email using Mozilla Firefox. I am including a screen print of the confirmation email sent by Mozilla for this user ID. I had to open and read it with IE. A rather irritating factor, this limitation.
There is an older bug filed for this, I'm making this as a duplicate of that bug.
Sorry, duped to wrong bug. Apologizes.