I've found a way to modify another theme to fit my liking of dark themes, but it starts out with more stuff than I want.
Since it's free, and the readme explicitly talks about not producing derivative works, I'll just give instructions on modifying the theme the way I do after every time the theme is updated:
Install the Nasa Night Launch theme (
https://addons.mozilla.org/en-US/firefox/addon/4908 )
Go to the firefox application data folder, your profile, then under "extensions\nasanightlaunch@example.com\chrome ", open the nnl-inner.jar file in 7-zip
Apply the following changes:
Delete:
\browser\inflight.2.gif
\browser\preferences\preferences.bg.15.png
\global\backgrounds\*.*
\global\subskins\toolbox-logo-8\nasa-logo-and-exhaust.alt4.png
\global\subskins\window-picture-2\window-bg.alt10.png
\global\subskins\window-picture-4\sts116-s-021.png
\global\watermarks\about.blank.sts116-s-021.v010.jpg
\global\tabbar\browsertab-gradient-*
\global\tabbar\browsertab-leftedge-* (Part of visible tabs)
\global\tabbar\browsertab-middle-* (Part of visible tabs)
\global\tabbar\browsertab-rightedge-*(Part of visible tabs)
\global\tabbar\tab-bottom-gradient-*
\global\tabbar\tab-gradient-*
\global\tabbar\tabstrip* (Tab strip background)
You'll shave about 1mb off the file size, when all of this is done, and though it won't be as dark as Full Flat Absolute Black, I've found it to be tolerable, and to have better compatibility with new firefox features.
I've been using this theme for a while on multiple machines, so I decided to make mention of it now that I'm confident that it's a good, consistent basis for a primarily dark theme.