How to install key in Thunderbird

Please find attachments field below the message body and the registration key file (for example, AccelMan #2-01-232123-234.fxregkey). Point at the attach name with the mouse cursor and then double-click on it

You can see the confirmation message. Please do not change default settings and answer 'Ok' to open the registration key.

Now the registration key installed and you can see successful notification on the screen. Please restart application to complete the registration.