Thanks for letting us know about the situation. We'd love to help you with this.
To add the "mailto:firstname.lastname@example.org" in the Footer behind the email address, you can follow these steps:
1. Double click in Footer content column-> Editor tab will open.
2. Enter the email address or any text in Footer-> Select the text
3. Editor tab-> Click on "Hyperlink"
4. Enter "mailto: email@example.com" in External URL
Please check the screenshot for your reference.