CANDDi uses Flash cookies as a (another) mechanism to store data (as well as regular cookies) to attempt to identify returning visitors to your site.
Firefox 29 and above are likely to help the user by prompting them when a site requires a plugin which isn't installed (or which is out of date).
Firefox is trying to help the User by pointing out that they should upgrade their flash (note the user will see this on any site which runs flash)
Options to solve this:
1. Do nothing-
In this instance, CANDDi will continue to use Flash Cookies to track visitors.
Firefox users will receive the pop-up above unless they install Flash (in which case it will go away)
This looks "a little" odd for your site's User Experience (but to be honest it's the same as Firefox users will see this on any site with Flash)
2. Turn off Flash cookies-
The other option is to turn off Flash Cookies,
Unfortunately there is no way to do this through the GUI (graphical user interface) at the moment - if you contact email@example.com then we can get this turned off in your tracker.
In this instance,
CANDDi won't use Flash cookies in any browser. This means that if a user clears their regular cookies (or upgrades their browser in some cases) then CANDDi is less likely to recognise them as a returning visitor