The stock price for the maker of Farmville and CityVille is down more than 12% in after hours trading, continuing a downward trend that has slashed Zynga‘s market value more than 72% since it went public last December. The latest decline follows the disclosure in an SEC filing that it has revamped the terms of its deal with Facebook: Beginning in April Facebook “will no longer be prohibited from developing its own games” according to the new terms. But Zynga now can introduce games on its own site, and doesn’t have to accept Facebook ads, steer transactions through Facebook Payments, or require users to sign in via the social network. Zynga games must be available to Facebook “shortly following” their launch unless there’s a technical problem or if they’re introduced in China or Japan. Zynga has been slashing expenses and realigning management as founder and CEO Mark Pincus said last month that it “did not execute to our satisfaction.” The company cited weakness in its Internet “invest and express” category, where players try to earn objects that they can display in the game. The company also said that it has taken longer than it anticipated to launch new games, and its web game The Ville could fall short of earlier expectations.