Not hosted at Mozilla you can only get this from the authors site. It’s real dark but very well done.
Midnight iPox combines the dark of MidnightFox and the bright blue buttons of iPox Aqua to create a pretty nice theme! Hats off to Jeremy for such a nice mashup.
To install, download the Midnight-iPox.jar file from the link above. Then open Firefox and go to Tools -> Add-ons and drag Midnight-iPox.jar into the left side of the Themes section. Once installed, restart Firefox to use it.