No menu configuration

Dear support team,
I upgraded to 4.4. Since then I am not able to edit the menu anymore. When I go to the menu site (Desgin -> Menu) the former edit area is not visible anymore. Only on the left I see the bar for sites and posts but everything else seems to be gone too. What happend to the menu editor?

(I use osx 10.7 and firefox 42).

Thank you!