Are you sure protected mode is disabled? Firefox has a hidden setting for this now.

  1. In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.
  2. In the search box above the list, type or paste flash and pause while the list is filtered
  3. 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.