I'm not sure if this helps, but when I see this I can see the blue focus ring on the address bar when my mouse is over Firefox, but when I move my cursor up to the GNOME panel at the top of my screen where my Application/Places/System menus are I can see the focus ring move to one of the shortcuts I have on that panel.
I do not have window focus set to follow the cursor.
I'm not sure if this helps, but when I see this I can see the blue focus ring on the address bar when my mouse is over Firefox, but when I move my cursor up to the GNOME panel at the top of my screen where my Application/ Places/ System menus are I can see the focus ring move to one of the shortcuts I have on that panel.
I do not have window focus set to follow the cursor.