how to call thunderbird instead of evolution from firefox
 

In the firefox packaged by Fedora, if you click
on a mailto: link, the mailing program which
is called is evolution, and I was unable to
find in the firefox preferences how to change
that. Anybody knows how to do that?
(I am new here, and expect that this question is actually in the scope of this forum)

Are you using GNOME? If so, click on Desktop -> Preferences -> Preferred Applications and change the default mail client.

Type about:config into the firefox address bar.
Then set
network.protocol-handler.app.mailto = /path/to/thunderbird

where /path/to = the path which thunderbird is installed on.

adding the new entry in about:config worked perfectly, but at last
I preferred to create it in file user.js, as it seems that there is
no guaranty that firefox doesn't delete it some day in prefs.js.
many thanks.