The nsIRelativeFilePref interface is a wrapper for an nsILocalFile and and a directory service key. When used as a pref value, it stores a relative path to the file from the location pointed to by the directory service key. The path has the same syntax across all platforms.
This interface is implemented by the following components:
The file whose location is stored or retrieved.
A directory service key for the directory from which the file path is relative.
Reference documentation is generated from Mozilla's source.