Unfortunately, this doesn't happen in the firefox-* packages. This is hardcoded in gnome-control-center itself.
It has to be listed in /usr/share/gnome-control-center/default-apps/gnome-default-applications.xml.
The proper way to fix this would be to teach gnome-control-center (capplet) how to read user files
in something like /etc/gnome-control-center/gnome-default-applications.d/*.xml that other packages could populate.
Unfortunately, this doesn't happen in the firefox-* packages. This is hardcoded in gnome-control- center itself. gnome-control- center/ default- apps/gnome- default- applications. xml.
It has to be listed in /usr/share/
The proper way to fix this would be to teach gnome-control- center (capplet) how to read user files control- center/ gnome-default- applications. d/*.xml that other packages could populate.
in something like /etc/gnome-