First, install Firedrake:
curl -O https://raw.githubusercontent.com/firedrakeproject/firedrake/master/scripts/firedrake-install
python3 firedrake-install
You will need to check out the following branches to enable the Wu-Xu element:
FInAT (wuxu)
ufl (WuXu)
tsfc (WuXu)
FIAT (toriesz)
Source the interpreter:
source firedrake/bin/activate
and you are ready to go!