  We present the open-source $\texttt{C++}$ library $\texttt{FireFly}$ for the
reconstruction of multivariate rational functions over finite fields. We
discuss the involved algorithms and their implementation. As an application, we
use $\texttt{FireFly}$ in the context of integration-by-parts reductions and
compare runtime and memory consumption to a fully algebraic approach with the
program $\texttt{Kira}$.
