hello and thanks for posting your question I have personally came across this problem as well and it is not a Firefox problem i have several solutions for you to try... First try to contact zynga support on this issue as we have no access to their system they have a live chat option its under the support tab and has a picture that looks like a chef from cafe world Also you may have blocked this app on face book i would suggest looking in your installed/blocked apps on face book and make sure it is installed if that is not the problem try removing the app and adding it back. ALL OF YOUR GAME INFO WILL BE SAVED SO DON'T WORRY Have a great day and thanks for using fire fox support