With TB 60+ a lot of old extensions are incompatible including my favourite nostalgy. Update: as of 23 Sep 2018 Nostalgy has a new version that is compatible with modern Thunderbird! Update 2: Nostalgy is broken for TB68+, but there’s a fork.
I now use Quick Folder Move (in combination with Dorando to rebind keymappings) & Folder Pane View.
Older extensions that are still compatible that I use are CompactHeader, Attach From Clipboard & Layout Button.