Default Browser - gnome-default-applications-properties not working?

[Schlueri]

After fresh FC1 install i've installed mozilla-firebird. In 
gnome-default-applications-properties i've set the option "user defined
webbrowser" to "mozilla-firebird %s". All working fine.

After some reboots i noticed that mozilla where used to open an url from
evolution instead of firebird. I set up the default application again.
It switched back to "mozilla %s" ever. I've tried to use gconf, same
effect.

What's happend? Open gnome-default-applications-properties from terminal
brings no debug output.

Any ideas to debug this thing?

Schlueri