Cookies that are not whitelisted get "unwanted" status which means that they are subject to deletion either periodically or upon browser startup (see Cookiebro Options page to define how you want it to behave).

In the Cookie Log there is column called "Decision" which is either "Set" or "Blocked". If it says "Set" it means cookie was stored and if it says "Blocked" it means cookie was rejected.

Firefox should be set to allow cookies so that Cookiebro can take care of the handling.