The blaze broke out in the attic of the three-storey residential building on the Route de Bonnesfontaines, north-west of the city centre, shortly before 2pm, Fribourg cantonal police said.
Fire fighters took almost three hours to bring the fire under control but had not completely put it out at 4.45pm, police said.
A fire fighter was taken by ambulance attendants to Fribourg hospital after receiving minor injuries while battling the flames.
The fire “ravaged” the third floor of the building but police could not put an estimate on the damage.
The cause of the conflagration was not immediately known.
A part of the Routes des Bonnesfontaines was closed to motor vehicle traffic for two hours while fire fighters dealt with the blaze.