As siduction is Debian sid, you already have firmware-linux-free because (one of) your sources.list points to debian repo. If you add "contrib non-free" in your debian.list, you have firmware-linux-nonfree from debian, too.
No need to have a redundant copy in siduction repos (Unless somebody would pack a special or patched version which would then probably go to extras or else, until upstreamed to debian).