To see it open firefox and click on view>toolbars>customize then click on themes at the bottom.
I like the way it shows the stars instead of the usual gradient backdrop. If you can get them to send you the original image maybe you can add it as a theme and wallpaper so when firefox is maximized it all blends together. Or make a similar theme and send it to them.
Feel free to contribute your own theme and upload to xfce-look.org or any other.
Anyway, not something to add in the core package anyway.