Do I need to download/upgrade

Thunderbird offers updates automatically once available. You can also manually check for updates: At the top right of the Thunderbird window, click the menu button ≡ > Help > About Thunderbird <blockquote> I was just contacted and completed a survey, and signed up for your newsletter. </blockquote> If you received an email then this sounds more like a spam or even phishing attempt. I doubt Mozilla would actively contact you via email to complete a survey. So be careful.