I feel so popular!
The name comes from the first scene of the first broadcast episode of Firefly
called "The Train Job" (Fox aired the episodes out of order).
In the scene, the patrons in the bar are toasting to the 6th anniversary of "Unification Day", which was the end of an interplanetary civil war between the Alliance and the Independents (browncoats). The Alliance won.
The hero (of the series), Captain Malcolm Reynolds, fought for the Independents.
He goes to the bar and orders another drink. The toasting patron stops him, noting that he didn't toast. Then he says, "You know, your jacket is kind of a brownish color."
Mal responds, "It was on sale."
This is funny to me because my mom is a big "on sale" person and by extension, so am I.
Didn't need it? Can't afford it? Doesn't matter! "It was on sale!"