ThreadKey 3.0
by Onno Ekker, Luca Porzio
Strike the 'T' key to sort messages by thread, strike the 'U' key to sort them unthreaded again, just like the 'G' key switches to Grouped By Sort view.
About this Add-on
Please note that the 'T' key is by default assigned to the menu item 'Go > Next > Unread Thread': this key assignment will be replaced by 'Shift+T'.