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 Mozilla Thunderbird for Mac. At the top, click on Tools and then Account Settings.
On the left side menu, select your email account at the top. On the right, paste your email signature into the section that says Signature text. Make sure you tick the “Use HTML” tickbox as this allows HTML attributes to be used in your signature.
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.