Letter g is inconsistent

[domoritz]

On https://fonts.google.com/specimen/Fira+Sans

[jfkthame]

I guess you're referring to the contrast between the "double-storey" and "single-storey" designs? This isn't a bug, it is a design choice; a font family may use the double-storey 'g' in upright faces, but switch to the single-storey design for italic. The same often applies to 'a'.

This is more commonly seen in serif families, I think, but is also a legitimate choice sometimes used in sans-serif families (including Fira). Some other examples:
https://fonts.google.com/specimen/Source+Sans+Pro
https://fonts.google.com/specimen/Merriweather+Sans
https://fonts.google.com/specimen/Kanit
https://fonts.google.com/specimen/Asap
https://fonts.google.com/specimen/Archivo+Narrow

[domoritz]

Thank you for the explanation. I hadn't noticed it in all the other fonts.