Difference between "Prahan yliopistossa" and "suomalaisessa firmassa"
I came across two sentences while doing exercises in a textbook.
1, Marja opiskelee Prahan yliopistossa tšekkiä.
2, Hän on työssä suomalaisessa firmassa.
Why is there used genitive with Praha and inessive with suomalais? Why not suomalaisen, when both yliopisto and firma belong to something (either city Praha or Finland). My guess is that it has something to do with the fact that Praha is a noun and suomalainen is an adjective. It is a bit confusing for me since in my mother language (slovak) we would use adjective both for Praha and suomalainen.
Thank you for help!