Missing old firefox? This theme is a combination between australis UI and photon UI, hopefully you'll like it :D
Restart Firefox.
Due to the experimental nature of Nightly Mozilla tends to break the theme, if you use Nightly uncomment the section: / NIGHTLY FIX /
Please note that this does NOT apply to Firefox Stable, Beta and Developer channels, it ONLY applies to Nightly channel.
If you experience any issues or you have a preference which is not included in the skin, open an Issue, and I'll have a look at it, you can also contact me via Reddit.