Good point, my GNOME3 desktop is using a "dark" theme and indeed the webpage background is suspiciously similar to the panels you can see above... I just checked the Search documentation and have the same!

I guess I can significantly lower the priority then, but there's still something wrong as I don't have the same problem with other websites.

This is a brand new Fedora 22 Beta.. one of its features is that L&F is "better integrated" with all non-gnome applications. For example Konversation (a KDE app) looks gorgeous. I don't have these problems with Chrome, but then again Chrome looks like identical as usual so maybe it's just the Firefox integration which went too far.