Mozilla released an important update for Thunderbird 16.0 with Thunderbird 16.0.2 on October 29th, 2012. Thunderbird 16.0.2 addressed these issues: Security vulnerabilities with Location object issues Bug 803843: IMAP based accounts could sometimes continuously download emails Existing Thunderbird 16.0.x users can update via Help > About Thunderbird or downloading and manually installing via the getthunderbird.com site.