Suddenly I cannot access the "Options" menu. It shows in the tab "Tools", but when selected Thunderbird locks up, requiring End Task from Task Manager. If I restart with all add-ons disabled, "Options" does become available. However, if I disable any one of the add-ons individually, "Options" locks up the app. Makes it impossible to isolate which add-on might be causing a problem. Thunderbird upgraded to this version (64.4.0) a week or two ago, but have not had the need to open "Options" until now. Unsure if the defect is due to this upgrade or something different. Nothing appears in the Error Console or Crash Reports. Thanks Doc