Dirty workaround:
...
UnimEditFirstname.CreateOrder := 1;
UnimEditFirstname.JSInterface.JSAddListener('painted', 'function(me){me.inputElement.dom.setAttribute("tabindex", "1")}');
UnimEditLastName.CreateOrder := 2;
UnimEditLastName.JSInterface.JSAddListener('painted', 'function(me){me.inputElement.dom.setAttribute("tabindex", "2")}');
UnimEditStreet.CreateOrder := 3;
UnimEditStreet.JSInterface.JSAddListener('painted', 'function(me){me.inputElement.dom.setAttribute("tabindex", "3")}');
UnimEditZIP.CreateOrder := 4;
UnimEditZIP.JSInterface.JSAddListener('painted', 'function(me){me.inputElement.dom.setAttribute("tabindex", "4")}');
UnimEditCity.CreateOrder := 5;
UnimEditCity.JSInterface.JSAddListener('painted', 'function(me){me.inputElement.dom.setAttribute("tabindex", "5")}');
UnimEditEmail.CreateOrder := 6;
UnimEditEmail.JSInterface.JSAddListener('painted', 'function(me){me.inputElement.dom.setAttribute("tabindex", "6")}');
...