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