The latest version of Firefox (version 13) is not compatible with the latest version of Flash Player (version 11.3).
So, the fastest solution is to downgrade Flash Player to Flash 10.3 or Flash 11.2
Step 1: Uninstall Flash Player 11.3
- To uninstall Flash Player 11.3, use the uninstaller provided by Adobe here.
- Close Firefox.
- Run the uninstaller.
Step 2: Install Flash Player 10.3 or 11.2
- Download Flash Player 10.3 here. If you want to use Flash Player 11.2, go here.
- Close Firefox.
- Run the installer.
After you have finish, open Firefox to see if flash is running. I have mine running. Hopefully this will work.
Have a great day =)