Chinese phrases are often inserted into the English dialogue (sometimes to get away with saying things that the censors wouldn't allow them to say), and the ship has some signs in Chinese.
Every scene in space is shot without sound effects of the ship moving, precisely as it would in real vacuum. No air, no sound. (Note this does not cover dramatic music that plays during space scenes.)
According to an oral history of Dr. Horrible's Sing-Along Blog published in July 2008 in [Entertainment Weekly], Neil Patrick HarrisNeil Patrick Harris auditioned to play the doctor role on [Firefly] that was eventually filled by Sean MaherSean Maher.
The cast had a running gag where they would yell Summer GlauSummer Glau's name whenever they flubbed a line or messed up. It began after she forgot her line at the end of a particularly difficult scene. The gag continued through the filming of Serenity.
The cast preferred to use the ship's lounge instead of a green room or other accommodations when waiting between shots.
The Alliance's full title is the "Anglo-Sino Alliance". Joss WhedonJoss Whedon intended the Alliance to be the merger of the USA and China, the last of the world's superpowers. (This is why many characters on the show sometimes speak Chinese.) The Alliance flag, seen in the original pilot episode, is a blending of the US and Chinese flags.
The entire interior of Serenity (and some of its exterior) was built full-scale and almost completely contiguous, split across two soundstages - one stage for the upper deck and one for the lower deck, shuttle docks and hold. No "stock" corridors or redressed sets were ever used for Serenity's interiors.