You can try removing the app from your Facebook account by going to Facebook > Settings > Apps > Angry Birds Friends > Remove app. Afterwards, you can relaunch it by clicking the link below.
Here are also other tips that may be useful:
- Clear the cache and cookies from your browser
- Check that your firewall or antivirus software is not blocking the game
- Check that you don't have "AdBlocker" or such plug-ins blocking the game
- Try playing the game with a different browser
- Check that you have the latest version of Adobe Flash Player installed