Assuming that your navigation is set up to automatically generate tabs, the contact form will now appear in the global navigation. If not, check your settings at Site Setup → Navigation Settings. When selected, the tab will be marked as current in the navigation bar, just like an ordinary content page.
Note, that the manage_propertiesForm is not available via the Zope Management Interface.
Many thanks to Espen Moe-Nilssen and Marcos Romero for this tip.