Like the comment above, I also feel that the official visual updates made after the latest version are really ugly. Plus, I simply cannot understand the decision to force the default theme on shared accounts.Fortunately, I found it.This theme gives me a sense of familiarity.:)

This one is really good. I've been searching for a good classic dark theme for firefox since the 'nova' (157) Update and this is exactly what I've been looking for. :)