I only see Light, default, Dark theme on my side so what themes are you talking about?

I'm not talking about themes that you have installed by default when you install firefox. I'm talking about the theme from the screenshot. The screenshot is the official download page for firefox 57 (quantum). This theme is interesting because it has black title bar with the gray stripe over the close/maximize/minimize buttons and it also has white navigation and url bar. I believe that it will look amazing with my userChrome.css setup I have at the moment. But I can't find it on the theme page, there are just too many to browse trough all of them

Sorry. We do not have that information. Support Volunteers are not told and no idea where to find that info.

Suggest google for it as someone else might be looking also.

Please let us know if this solved your issue or if need further assistance.