This is from the Ford Fiesta Owner's Manuel.
Recreational Towing Note: Put your climate control system in recirculated air mode to prevent exhaust fumes from entering the vehicle. Follow these guidelines if you have a need for recreational (RV) towing. An example of recreational towing would be towing your vehicle behind a motorhome. These guidelines are designed to ensure that your transmission is not damaged. Vehicles with a Manual Transmission Your vehicle can be towed with all four wheels on the ground or with the front wheels off the ground by using a tow dolly. If you are using a tow dolly, follow the instructions specified by the equipment provider. If you tow your vehicle with all wheels on the ground, follow these instructions: 1. Tow only with your vehicle in the forward direction. Release the parking brake. 2. Place the transmission in neutral. Note: Do not exceed 70 mph (113 km/h) when towing your vehicle.
Just a note from someone that once towed for AAA.
You should never flat tow a vehicle with an automatic transmission unless it is equipped with a transmission disconnect.
Also, the steering column must remain un-locked.
I would have to say that since the Fiesta ST has neither an automatic transmission nor a steering column lock, it is safe to flat tow.