Thread:Project:Support desk/Versions required to run "Usability Initiative" and updated "Vector" skin/reply (2)

The collapsible navigation is created using the Vector extension. Do an update to MediaWiki 1.19. This version is still supported (e.g. with security updates) and it contains the Vector extension. After the update you will have to install and configure the extension; more information on that topic are available on the page Extension:Vector.

If you want to update to MediaWiki 1.20 in the future, note that you will need a newer PHP version first: MediaWiki 1.20 needs PHP 5.3.2 at least. (And it contains Vector as well.)