Thunderbird - How do I inform MacOSX thast thunderbird is my prefered mail program?

In several applications such as iPhoto, iTunes, FireFox, we have options
to email some selection (for example a photo, or a tune, or a link);
The problem is that I find no way to configure Thunderbird as my prefered
mail program. 
Thunderbird does execute properly, but for example does not show up in
iPhoto as a possible mail program to select (other mail programs, such as
Mail, AOLmail, Eudora) do show up, but not thunderbird.

Thanks
Please let me know if this is the proper forum for this message