Yes, now the collection is completed. Mumei from Koutetsujou no Kabaneri is also available as a Firefox theme for you to enjoy. Just like the AIMP3 skin project, I have been so long abandoned the Firefox theme. It’s quite refreshing to be working on this theme again especially when Mumei is on the main spotlight.
Skin Name: Mumei
File Size: N/A
Color Theme: Red & Black
Download: https://addons.mozilla.org/en-US/firefox/addon/mumei/
Note: Installation of this skin can be observed here. Don’t forget to follow the instruction presented in the link. Happy downloading!
Randomness Thing 
Not Mumei tho, Its Nero > w <
If you are talking about our website’s header image then yes, it’s Nero. But the Firefox browser theme is Mumei.