In this note we give equivalent characterizations for a fractional Triebel-Lizorkin space F_{p,q}^s(\Omega) in terms of first-order differences in a uniform domain \Omega. The characterization is valid for any positive, non-integer real smoothness s\in \mathbb{R}_+\setminus \mathbb{N} and indices 1 \leq p < \infty , 1\leq q \leq \infty as long as the fractional part s is greater than d/p-d/q.