Are you sure protected mode is disabled? Firefox has a hidden setting for this now.
- In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.
- In the search box above the list, type or paste flash and pause while the list is filtered
- Double-click the dom.ipc.plugins.flash.disable-protected-mode preference to switch its value from false to true.
This might not take effect until all Flash has been unloaded for a few minutes, or you close Firefox and try again.
Note: Please make sure that your Video drivers and Flash plug in are up to date.