If you find you still receive the same message ("This feature is disabled. It is available for Internet Explorer 6+ only.") in 32 bit mode, the details below will help;
In IE11 (X86, 32-bit mode), click Tools>Compatibility View Settings
Add ariba.com
Close all IE11 browsers
Re-open/login to Ariba and DFS can be enabled.
Cheers,
Ben