I'm using Firefox Developer Edition as I was when using UbuntuGnome 16.04. It respected the global dark theme and the title bar was dark.
Now due to a new hard drive, I have freshly installed UbuntuGnome 16.10 and turned on the global dark theme. All other applications and windows are respecting this setting and have dark title bars except for Firefox!
I assume this is a bug but in the meantime where can I manually change the colours?
Thanks!
It seems like a bug indeed: "Title bar is using the light theme when the dark theme is selected on GNOME 3.22"
I haven't found a way to change it manually but you can use the GTK Dark Theme Addon, which "make the window decorator dark to match Firefox's dark theme".