What used to be the held on the first Monday and Tuesday of December, the Cast Member parties at Disneyland Park (aka employees) have been moved in 2010. The scheduled days are now December 13th and 14th. That means the park closes at 6 PM, with Fireworks at 5:45 PM (weather permitting). California Adventure will remain open to 9 PM, with showings of World of Color.
The rest of the week, Disneyland is open to Midnight due to the expected large crowds.