These .FSF files are just stored settings from the adjustments in the Film tab: Saturation, Tint, Noise Reduction, Contrast, Edge Enhancement, and (if you have selected the black & white option) a monochrome filter.
The idea is that if you have a particular set of adjustments that you like for a particular type of picture, you can store them in one of these FSF files (by clicking the 'Save' button) and then load them later for re-use by clicking the 'Load' button.
This feature would be more useful if the FSF files also stored special settings you made on the other tabs, such as tone adjustment and vignetting correction... but it doesn't, only the six adjustments on the left side of the Film tab.