Steps to reproduce: Nothing! I walk away from my Mac at night. When I come back in the morning, all of my normal apps are available and running fine (including Firefox). However, Thunderbird is unresponsive. Clicks made on the active mail area "Subject" aren't recognized. However, I can quit Thunderbird and relaunch it with it then normally opetational. Actual results: Thunderbird was unresponsive. Expected results: Click on Thunderbird and all functions are available.