Note: When installing your email signature in Thunderbird, you need to use the HTML source code of the email signature.
Once you are ready to set up your email signature, open Thunderbird, at the top right, click the Settings icon and select Options then Account Settings.
On the right side paste your new or updated email signature into the Signature text field. Be sure to select “Use HTML” if it isn’t already ticked.
Click the OK button and click to compose a new email message. Enjoy your new signature!
Note: Thunderbird will often show red borders inside and around the email signature when you compose a new email. Those borders will not be visible to your recipients, and your email signature will look normal to them.