Facebook Privacy Watcher is a Firefox addon to help you manage Facebook privacy settings using colour codes. Instead of having to pay attention to checkboxes and tiny text in Account Settings> Security hoping that you got everything right, Facebook Privacy Watcher will visualize public posts in green, friends only posts in orange, red posts only visible to you and blue coloured posts only visible to a subset of friends.
You can change any post privacy setting with a couple of clicks, colouring also works in your profile and photo albums. The addon runs in your browser no data is sent to the developer.
This addon is not yet available in the official Mozilla addons repository but it is partly developed by the Technical Univeristy of Darmstadt which should give some peace of mind about malware.
Other security measures you might want to take to secure your Facebook account are linking it to a mobile device, enabling always on secure HTTPS browsing, choose a strong password and set up login notifications where Facebook warns you when your account is accessed from a device not previously used.