Thank you very much for the solution. I’ve been at work since this morning, and instead of actually working, I’ve spent the time installing and testing dozens of different Firefox themes just to get rid of that terrible look. I don’t mind having various themes and settings available, but I’m against having them forced on me. Let everyone have a choice. I’ve been using Firefox for over a dozen years and consider it a great browser, but if this setting couldn't be changed, I probably would have switched to a different one.
