[http://community.bitdefender.com/discussion/comment/356351#Comment_356351 Solution update posted at 8:48 Eastern time (12:48 UTC) Thursday by Alexlandru_BD], an admin at bitdefender, "The developers reverted the changes made in the last signature update and this should do the trick until a permanent fix is deployed. Just click on update in systray and reboot once completed. But keep in mind this change is being rolled out gradually, so it may not reach everyone at the same time.." More details at https://www.reddit.com/r/Thunderbird/comments/1mo693n/comment/n8ammvq/