  We study integrable models solvable by the nested algebraic Bethe ansatz and
described by $\mathfrak{gl}(2|1)$ or $\mathfrak{gl}(1|2)$ superalgebras. We
obtain explicit determinant representations for form factors of the monodromy
matrix entries. We show that all form factors are related to each other at
special limits of the Bethe parameters. Our results allow one to obtain
determinant formulas for form factors of local operators in the supersymmetric
t-J model.
