If you happen to be on Linux, then it's likely one of these: https://askubuntu.com/a/1148258

Could it be "Fira Sans"?

https://mozilla.github.io/Fira/

I don't know the answer, but the devtools inspector should work in that view too, I think. If you use it's tool that selects the element on which you have clicked, you should see the list of fonts in order of preference on the right, which is the CSS viewer. To check which one it is, you could remove fonts from the list one by one