Hello,

One year ago, Roel Janssen sent a patch adding this font but finally it
wasn't applied. I created a new one, building the fonts from source, and
it includes all fira mono family: Bold, Medium and Regular.

I'm downloading the sources from carrois.com website because from github
isn't possible to download only the Fira Mono font, Fira Sans is also
included. I checked the nix package and they are doing the same. 

Cheers,

Toni