How do I view the full email header in Thunderbird? 

Here are the steps to viewing the full email header in Thunderbird.

1. Find the email you want to view the full header for and open it.

2. On the right, just above where the message is displayed, there will be an 'other actions' link.

3. Click the link and select 'View Source' from the drop down menu.

4. A new window will open up with the full email header.