Starfall is an Exile holiday that remembers the day that the wandering fleet crossed the galaxy to discover the Eldan planet. For the Exiles, Starfall marks the end of their journey and the beginning of a new home. It's a weeklong celebration that includes plenty of games, including Kiss the Matria (chances are that's a lot less sexy than it sounds). The festival is capped by an enormous fireworks display put on by the Alchemist's Guild.
Foundation Day, on the other hand, remembers both the foundation of the Dominion Empire and the establishment of Nexus as its new homeworld. Contrasted with the rough-and-tumble celebration of Starfall, Foundation Day is far more regal and official. After all, speeches are way better than kissing Matrias, right?
Both Starfall and Foundation Day come around about the same time each year, and depending on a player's allegiance, she might find herself engaging in a different celebration than her friends.