mozilla firefox about:config

[Peter Easthope <peasthope@cablelan.net>]

I've spent a good part of the day trying to
arrange that thunderbird is invoked when
I click on a mailto link in the firefox.

I created the file
~/.mozilla/firefox/qi0tjy0b.default/user.js
containing the line
user_pref("network.protocol-handler.app.mailto","/home/peter/firefox.mailto.sh");

Yet about:config in firefox lacks the
network.protocol-handler.app.mailto
record.

Any ideas?

Thanks,            Peter Easthope