Heading down the rabbit hole…
Qwikiverse maps the references between stories: what Firefly nods to, and what nods back. How it works
Wikipedia: Firefly (TV series)
The media may be obtained from Firefly (TV series).
Fair use
Nothing spotted here yet.
A line quoted, a cameo, a character named after something: if Firefly nods to another story, or another story nods to it, spot the first one.