Sending mails by right clicking on a file: how to replace Evolution?

[Stegozor]

Hi everyone,

My newsbie questions continue: Imagine an Ubuntu account for which 
Thunderbird is the default mail/news client. That still doesn't force 
the use of Thunderbird when one right clicks on a link on his desktop 
and chooses send to... option. The windows that's opened just after 
displays only Evolution in the menu.

Evolution is probably a good piece of software, but as I'm used to 
Mozilla products since I've been using Windows until recently, I'd like 
to stick to them. How can I use Thunderbird to send files on the desktop 
by right clicking on them and then on send to ? TIA.

PS: Thunderbird _is_ already the default mail/usenet client. In 
System>Preferences>Preferred applications (or very close, I'm using a 
desktop in French), I see mozilla-thunderbird %s in the Command field, 
and Mozilla Thunderbird is set as the default application.