I remember there were several issues with Firebug being detached into a separate window. I assume you are referring to
issue #7623.
A workaround for this problem is to use Firebug in attached mode, i.e. do
not have it as a separate window.
As I wrote in
the other thread you started, Firebug as extension is going away, so you are advised to use the
Firefox DevTools, which do not have this problem.
Sebastian