Hi,
I also hit this issue. However, I had upgraded thunderbird to 52.4.0-1 about a month ago, but only noticed this issue this week. One thing that changed for me this week is that I'm now running a kernel with AppArmor enabled. I suspect this issue might be AppArmor related, though I haven't seen any specific DENIED messages obviously related to it in /var/log/kern.log. -- Earthling Michel Dänzer | http://www.amd.com Libre software enthusiast | Mesa and X developer