It's been a long time since I've used Thunderbird, but if I remember correctly, you can open the address book by pressing Control plus Shift plus B. You can also find this option in the  tools menu. When you find the contact you want to delete, simply press the Forward delete key. It may ask you to confirm. In that case, press OK or Yes, and you should be good to go. I hope this helps.
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Abbie Johnson Taylor, Author https://abbiescorner.wordpress.com

http://www.abbiejohnsontaylor.com

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