It's a full html-mail. The critical part:

Content-Type: text/html; charset="utf-8"
Content-Transfer-Encoding: 8bit

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns:v="urn:schemas-microsoft-com:vml"><head><title>Weekly News</title>

- Same with you?
- If you go View>Message as, how does it look in the three options?
- It could be caused by an add-on. Try Help>Restart with add-ons disabled.
- It could be some strange setting the profile. Set up Thunderbird in a new Windows account. If it's OK there, deleted/rename the Thunderbird profile in your normal account. It will create a new one when you run it again, juat like it did in the new Windows account. Make a backup of the profile first!