Let $D$ be an integral domain with quotient field $K$, $E$ be a $K$-vector space, $R = D propto E$ be the trivial extension of $D$ by $E$, and $w$ be the so-called $w$-operation. In this paper, we show that $R$ is a $w$-FF ring if and only if $D$ is a $w$-FF domain; and in this case, each $w$-flat $w$-ideal of $R$ is $w$-invertible.
