Note: When installing your email signature in Thunderbird, you need to use the HTML source code of the email signature.
Step 1:
Once you are ready to set up your email signature, open Thunderbird. On the top right, click the Settings icon and select Account Settings.
Step 2:
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.
Step 3:
Click to close the Account Settings window and 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.
This does not work in Thunderbird 102.4.1 (64-bit)
Thanks, Christian. The instructions have just been updated.