I’m in the minority who believes Fox was right to start Firefly with the Train Robbery, so what do I know? :) (I know my wife fell asleep 1/2 way through the original pilot.)
There are problems with Season 1, Season 2 has a better hook and because they replaced the commander and are doing a bunch of catch up work, there’s no harm starting there then circling back.
Season 1 is a slow burn and there are a lot of filler episodes that don’t go anywhere (looking at you Infection, Deathwalker, Believers, TKO).
That being said, the must watch season 1 episodes: