Same as forestpiskie: I don't have Lightning installed at all and have the same issue, which I reported here: https://bugs.launchpad.net/ubuntu/+source/thunderbird/+bug/934155
Same as forestpiskie: I don't have Lightning installed at all and have the same issue, which I reported here: https:/ /bugs.launchpad .net/ubuntu/ +source/ thunderbird/ +bug/934155