I lived in Pars in 1970 when I worked for Ford France. Back then French fire services including Paris still had yellow beacons on their trucks, just as they did in Spain too. Interesting that this PSM has been restored with a blue beacon, which was not adopted until later! The PSM was a version of the "premier secours" light pump which carried a foam branch and cans of foam for class B fires. It was usually crewed by five, had a 1000 LPM pump and a small water tank with a first aid hose reel, in addition to the traditional one man hose cart.
They are windows, installed to enable the driver to see the road at a different angle for close maneuvering. A unique and rather odd feature of this generation of Citroen trucks, which put styling ahead of function, as also demonstrated by the four headlamp setup with only two headlamps!
Added by Rob Johnson on 01 November 2021.