Due to security policies put in place by Mozilla, the developer of Firefox, Adobe Flash must be "allowed" to enable the plugin on webpages running Flash Player.
This security measure affects CustomShow, which must be allowed to run Adobe Flash Player.
For users working in CustomShow with Firefox, please be sure to enable Flash Player when launching CustomShow.
On startup, click on the Activate Adobe Flash button at the center of the screen.
Then, click on the Allow and Remember option in the plugins menu in the top Address Bar.
This will ensure that Flash Player can run CustomShow in Firefox in the future, and users should no longer be prompted to enable Flash in CustomShow.