Though television audiences only got to spend 10 episodes with Firefly, the series left quite the impression. With its mix of cultures and genres, its Civil War inspiration, and its larger-than-life characters, the show easily found a small but dedicated fanbase to promote it for years after its cancellation. Since the show's end, the games, the movie, and the comic books have further expanded the 'Verse, allowing fans to meet new characters and travel to new places in an expansive colonized solar system.
Only a handful of locations are visited in those properties, though many are referenced. Much of the show and the movie is simply set in the Firefly class spaceship, Serenity herself. There are several locations, however, that are incredibly important to the characters and the mythology of the franchise, whether the audience gets to spend significant time there or not.
Persephone
Without the existence of Persephone, Serenity wouldn’t have her newer passengers, or a port in a storm to stop and refuel. Persephone is one of the planets that wasn’t part of the original Alliance, which helped kick off the Civil War. Instead, it was one of the leading planets to house Independents, who were struggling to maintain their freedom from the Alliance that ends up ruling the solar system.
As a result, it’s home to a lot of colorful characters and criminals despite having an incredibly old-fashioned society where duels between men are as commonplace as Victorian-era-like balls. It’s on Persephone that Kaylee convinces Book and Simon to become paying passengers of the Serenity. It’s also on Persephone that Badger has his base of operations, allowing for a recurring character who trades with the ship and offers up jobs for the smugglers. Persephone is integral to keeping Malcolm Reynolds and his crew flying.
Sihnon
Sihnon is never visited onscreen, but it is repeatedly referenced in the series. It’s Inara’s home planet, and it’s where Companions are trained in their line of work. It’s also one of the heavily pan-Asian influenced planets.
The idea behind Firefly is that hundreds of years in the future, Earth-That-Was is no longer habitable for human life. As a result, the biggest superpowers in the world create teams to terraform and colonize new planets. China is one of those superpowers, hence the prolific use of Mandarin in the series. Sihnon is one of those main colonies.
Of course, the planet is also the location of the “Academy” River Tam is sent to as a child. It’s where the Alliance-controlled academic program gives way to scientific experimentation. Sihnon, then, creates two of the most important female characters in the series in very different training grounds: Inara and River.
Haven
Technically, Haven is not a planet. It’s a moon, specifically of the planet Deadwood. It is such an important place for the Serenity crew, though, that it deserves a spot amongst the most important planets. The moon is introduced to the audience through the movie Serenity, though it’s also referenced more in the novelization of the movie and in some of the comics that bridge the gap between the television series and feature film. Haven is, as its name implies, an actual haven for travelers.
Haven is where Shepherd Book makes his home after the events of the television series, and builds a faithful congregation. Some members of his congregation are likely not just from mining families (which the moon is known for), but also criminals. This is likely because the moon is also known as a place where former criminals and smugglers can hide out for a small fee, or where they can settle down when their running from the law is finally over. It’s clearly a place where the crew of Serenity feels at home when they visit Book and mingle with locals. It’s also the heartbreaking site of Book’s death when members of the Alliance are after Serenity.
Hera
The audience doesn’t spend a lot of time on Hera. It’s mainly seen in a handful of flashbacks to Malcolm Reynold’s time in the Unification War. However, just because the audience doesn’t see a lot of it doesn’t mean it isn’t important. In fact, it’s likely that if the series had continued, the audience would have seen quite a bit more of this planet as a result of the emotional significance for Mal, and potentially for Zoe as well, since the two served together in the war.
Hera is very similar to Earth. It was also one of the three major planets on the side of the Independents during the war. It is home to Serenity Valley. Serenity Valley is one of the bloodiest battles in the War for Unification, and it’s the place where Mal truly lost his faith as the war was lost, and the Alliance took over. Despite how hard the battle was, Mal named his spaceship after it. It’s a reminder of his own independence.
Miranda
Like Haven, Miranda doesn’t appear until the Serenity movie. Unlike Haven, Miranda is not a place where the crew feels at home. Instead, it’s a secret planet, full of mystery and death, which the crew tracks down only after River Tam unlocks her own memory of it.
After being experimented on by the Alliance, River often has trouble distinguishing between reality and what’s just in her head. Her memories are often confused, and her speech doesn’t always make sense to those around her. As she slowly begins to dig inside her own memories of her time with the Alliance, however, the name Miranda stands out, and she goes so far as to take over the ship and set a course for the planet that was presumed to be a failed terraforming event.
What the crew finds when they land on Miranda is one of the dirty secrets of the Alliance. Terraforming worked just fine there. The drugged air that was meant to make the population docile, however, killed many the people who lived there. The rest, it turned into Reavers, the cannibalistic people who live on the fringes of the occupied solar system. It’s a big reveal for the movie that could have certainly changed the way the public saw their government as the news of the cover-up spread.