Since you are using the beta, I encourage you to participate in the beta forum at https://thunderbird.topicbox.com/groups/beta You should anticipate bugs will be the norm in the beta and it is not recommended for day-to-day use. I periodically use the beta and there are a number of features that are not working, but are being tested for eventual rollout to the release version. If you do not like the automatic upgrades, you can change that at settings>general.