I heard it messes with mozilla firefox

It's a Nvidia driver bug, so if you're not on Nvidia you should be good.

Im getting slight fps drops that dont seem to relate to the steam fps counter.

You could try enabling mangohud with the full config. From steam launch options:

 MANGOHUD_CONFIG=full MANGOHUD=1 %command%

This will give you more detail than just FPS, although if you don't still have your old setup it would be challenging to compare.