We are aware of the game not loading correctly on Firefox and Microsoft Edge browsers. As we have not made any changes to the game or the services on our end, we have contacted Facebook to figure out what has been changed.
Update September 4th: Facebook has confirmed that they have also not made any changes. This means that the browser developers have likely blocked all Flash content that has been embedded from outside of the current page.
We recommend you to please use Chrome, Internet Explorer, Opera or Facebook Gameroom to play the game.
In case you are on Windows 10 device, you can also use the new version that is available in the Windows 10 Store - https://www.microsoft.com/en-us/p/angry-birds-friends/9nn6g50qnl1h