My Thunderbird email client has frustratingly dropped its Subject column in the Unified view of my Inbox. Whilst I have "fixed" the problem in the three individual email Account displays I have not been able to make it re-appear in the Unified display. The part-fix was achieved after finding a recommendation on this site to:- 1. Try the 'Restore Column Order' menu item - which didn't work. 2. If that doesn't help open a folder that has the correct columns, then click the selector icon at the end of the column buttons, Apply columns to... and select the defective folder - which did work other than for the Unified view. How can the the Unified view be fixed?