If your Firewall Builder configuration includes lots of objects then you will probably like user defined subfolders. This feature was added in v5, which is currently in beta, and lets users create subfolders below any of the standard predefined system folders.
After the subfolder has been created you can drag-and-drop objects from the system folder into the subfolder. These subfolders make it convenient to organize objects by region, location, function or whatever grouping makes sense in your environment.
The image below shows an example of using subfolders in the Firewalls system folder to organize firewalls by the city that they are located in.
More information about creating and managing subfolders can be found on the preliminary documentation here.