Wikipedia reports: [edited]
Fira Sans (initially called Feura Sans)is a sans-serif typeface designed by Erik Spiekermann and Ralph du Carrois of Carrois Type Design for the Mozilla Foundation.
Fira Sans is available in four weights with corresponding italics: light, regular, medium, and bold. There is also a monospaced variant, Fira Mono, available in regular and bold.
Available from Font Squirrel