Thanks for clearing that. I also need to explain my info. I never meant that people will change system colors. It's only a setup inside Firefox that overrides the colors of websites. (A pref)
The other option (Stylish) is a popular add-on (for Firefox) that works as a "click and forget" solution to style the web.
Very cool thing that remembers your settings for certain sytes so you can choose that hotmail will be always dark with matching texts etc.
There are also general styles that'll fix all this issues in few clicks(install and forget)
The styles are shared as we share our skins on userstyles.org
Firefox is great because it can be customized and millions are doing so happily.

Of course i don't expect people to change system colors , that's also why i include a "normal" sub-style that uses white background and black text and will have no visibility issues with any program or site!
We both know that within the limits of WB , any dark theme must compromise a little with visibility issues.
I did my best to minimize the issues, using it everyday(also to write this comment 
I still think we shouldn't give up the whole idea of dark themes.
Hope this helps to clear the subject and hope my tips help to make the theme smoother for people that like it dark.
Thanks for the feedback.