1. Everyone will be shocked when it's learned that Jayne is an alien lizard creature for some reason.
2. Due to the popularity of Star Wars Episode III, there will be a scene where they go to a lava planet. Once there they meet a lava monster that chases them when they try to take the treasure of the pirate ghost.
3. Everyone becomes ventriloquists.
4. Six little words: Tap dancing, Tap dancing, Tap dancing!
5. The 'Verse itself is rocked when there is a distressing Pudding Shortage!
6. It is learned that the thing that The Institute(or The School or whatever that scary place she was at is called) did to River is made her a Boggle champion, which becomes important in the final scenes when she plays Boggle against Galactus Eater of Worlds.
7. Wash joins the X-Men for some reason. His mutant power? Ability to make plastic dinosaurs talk.(eh, I was in the Marvel 'Verse anyway)
8. Everyone comes to realize that the number 8 is never used on the show and that it's because in the future the number 8 will be outlawed because of it's importance in... well, I can't say as it would give too much away. But I'll give you a hint: The Great Burrito Wars.
9. Boredom will cause a 26 fan of Firefly to make a pointless list of really fake spoilers.(see? that one's true, so the rest must be too. Or something)
10. The Crew of Serenity learns that somehow Badger is everyone's Father, though exactly how is saved until the sequel "Serenity 2: Electric Bugaloo".
There, hopefully this doesn't spoil the movie too much for everyone, but you can't say that I didn't warn you many times that there were spoilers and that they are all fake. Please don't hate me.