XCOM: Enemy Unknown – Disable startup videos [Steam/Mac]

To disable startup videos for the Steam Mac version of XCOM:Enemy Unknown do the following.

Disclaimer
Follow these instructions at your own risk. There is no guarantee that these instructions will work for you. I am not responsible for any damage or loss caused due to carrying out these instructions.

1. Find the file DefaultEngine.ini in
   ~/Library/Application Support/Steam/SteamApps/common/XCom-Enemy-Unknown/XCOMData/XComGame/Config
2. [recommended] Create a backup of the file. I called mine: DefaultEngine.ini_backup
3. Open DefaultEngine.ini using your favorite text editor – I used Sublime Text 3.
4. Locate the header ; PC Startup movies. The exact line number may vary depending on the DLCs you have installed. For me it was on line 1957.
5. Add a semi-colon (;) before the first four lines that start with +StartupMovies=. The semi-colon comments these lines out. If you like, you can include an optional space after the semi-colon. Leave the +StartupMovies=[screen_x_resolution]x[screen_y_resolution]_Black line as it is.
   
6. Save and close DefaultEngine.ini.
7. Startup XCOM: Enemy Unknown. If goes well the game should bypass the startup movies and go straight to the main menu.

Reference: StackExchange Gaming post by xenphilos