Today being the 23rd anniversary of the premiere of Firefly, I am both, doing a rewatch of the series as it aired should have aired, and started a new community for discussion of the show and related spin-off media.
https://en.m.wikipedia.org/wiki/Firefly_(TV_series)
Put on your browncoat and join us.
Opening scene is the battle of Serenity Valley, it cuts away to the crew collecting illegal salvage and having a close call with the Alliance, they pick up Shephard and Simon as passengers / commuters on Persephone which I think is the scene you’re referring to.