Firefox and Rhythmbox entries

Hi all,

I've installed GNOME Do and it works great!

However, with some applications, it doesn't work that well. For
example, I can type Evolution and the application will start. The same
for Pidgin. But when it comes to Firefox or Rhythmbox, it doesn't
work.

I tryed mozilla, mozilla-firefox, mozilla firefox, firefox but none of
these terms works. For Rhythmbox, there's not many options, Rhythmbox
and Rhythmbox!

What am I doing wrong? Is this normal? What can I do to make GNOME Do
recognise these applications when I write their names in?

Thanks in advance for your help,
Blacko