Hi Roman,
sorry for the late reply, I was on a longer vacation and saw this only now.
As far as I know, there is no implementation of the GeoFire composite in satpy yet (defined as combination of GeoColor with Fire Temperature RGB, using the thresholds as defined in the Quick Guide).
However, I have developed something similar for FCI (then also expanded to VIIRS), called "flames". The concept is similar, but with the difference that the fires are not colorised using the Fire Temperature, but rather with a custom colormap applied to IR3.8+NIR2.2, and that I used a simple, custom fire detection code for the mask.
Following along the lines of this composite, it should not be too hard to implement the GeoFire version as defined by CIRA.
Let us know if you have any other questions,
Cheers,
Andrea