Avast AVG and Mcafee are known to cause problems with update. If you use Avast, try the suggestion at https://support.mozilla.org/en-US/questions/1384853#answer-1525849 Other possibilities, are you running with a VPN or proxy? If none of those items have helped 1. Do Settings > General > type "config" into the search 2. Open Config Editor 3. Search at the top for "app.update.log" and set it to "true". 4. Restart Thunderbird. 5. Do Help > About 6. Open Tools > Developer Tools > Error Console 7. Type AUS into the filter at the top 8. Copy everything starting with "AUS:" 9. Please paste the information here.