'Angry Birds' slings onto Facebook "Angry Birds," the massively popular mobile game, made its debut on Facebook on Valentine's Day. "Angry Birds" makes its debut on Facebook The wildly popular game appeared on the social-networking site Tuesday Game will be free to play, but players must pay for bonus items and abilities (CNN) -- We're going to feel a little guilty if this news gets you fired. But you can now play "Angry Birds" on Facebook. Rovio's ridiculously addictive mobile game, which has been downloaded more than 500 million times on multiple platforms since debuting on the iPhone in 2009, hit Facebook on Tuesday. While the company had leaked out news that the merger of the game's millions of fans and Facebook's hundreds of millions of users was coming, a Facebook "launch event" was scheduled for 6 p.m. ET on Tuesday. But players, including, presumably, the 15 million who were already fans of the game on Facebook, can start slingshotting their feathered friends now. In addition to allowing players to pay for special in-game tools, such as more powerful birds, the Facebook version of "Angry Birds" also adds a social-gaming element. Besides posting their scores to their News Feed, players can send in-game gifts to friends and get special rewards for earning some of the game's highest scores. Rovio's chief marketing officer (or "Mighty Eagle" in bird-speak) Peter Vesterbacka told the blog Penn Olson that the Finnish company hopes as many as 40% of players will pay for bonus items -- a far higher rate than for other social games like "FarmVille" or "Mafia Wars." Upgrades will cost 99 cents each. From an early look, the game appears to play much like the original version that appeared on iOS devices. The difference, obviously, is that players use a mouse instead of a finger to pull back the bird slingshot. They also must toggle the screen size up and down on a sliding scale instead of pinching a touchscreen. It's a play style that will be familiar to people who played the game on Google Chrome -- a version that rolled out last year. Players can switch to full-screen mode (which is sure to be noticed by your boss, unfortunately) and personalized avatars will be available soon, according to the company.