“I recently moved from Mozilla to Firefox 1.0PR for Web browsing
on my Fedora Core 1 Linux desktop system. On that platform, Firefox
doesn’t do anything with mailto: links by default; it just prints
an error message if you click on one. However, a Firefox extension
called mozex allows you to use any external mail program for
mailto: links in Firefox.“Note that Firefox on Windows does understand mailto: links, and
will open the mailer you specify in your Internet Properties
control panel. However, if you want to use an arbitrary program
that doesn’t register with that control panel, mozex works fine on
Windows, and gives you other useful features I’ll discuss
below…”